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The GNU Troff Manual

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Footnotes

(1)

What You See Is What You Get

(2)

The same is true for the other main macro packages that come with groff: `man', `mdoc', `ms', `mm', and `mandoc'. This won't work in general; for example, to load `trace.tmac', either `-mtrace' or `-m trace' must be used.

(3)

This section is derived from Writing Papers with nroff using -me by Eric P. Allman.

(4)

If you need finer granularity of the vertical space, use the pvs request (see section 5.19.1 Changing Type Sizes).

(5)

Actually, only the title is required.

(6)

For an explanation what special characters are see 7.1 Special Characters.:

String: \*[-]
Prints an em dash.

String: \*[*Q]
String: \*[*U]
Prints typographer's quotes in troff, plain quotes in nroff. *Q is the left quote and *U is the right quote.

Improved accent marks are available in the `ms' macros.

Macro: .AM
Specify this macro at the beginning of your document to enable extended accent marks and special characters. This is a Berkeley extension.

To use the accent marks, place them after the character being accented.

The following accent marks are available after invoking the AM macro:

String: \*[\']
Acute accent.

String: \*[\`]
Grave accent.

String: \*[^]
Circumflex.

String: \*[,]
Cedilla.

String: \*[~]
Tilde.

String: \*[:]
Umlaut.

String: \*[v]
Hacek.

String: \*[_]
Macron (overbar).

String: \*[.]
Underdot.

String: \*[o]
Ring above.

The following are standalone characters available after invoking the AM macro:

String: \*[?]
Upside-down question mark.

String: \*[!]
Upside-down exclamation point.

String: \*[8]
German ß ligature.

String: \*[3]
Yogh.

String: \*[Th]
Uppercase thorn.

String: \*[th]
Lowercase thorn.

String: \*[D-]
Uppercase eth.

String: \*[d-]
Lowercase eth.

String: \*[q]
Hooked o.

String: \*[ae]
Lowercase æ ligature.

String: \*[Ae]
Uppercase Æ ligature.

4.3.7 Differences from AT&T `ms'

This section lists the (minor) differences between the groff -ms macros and AT&T troff -ms macros.

4.3.7.1 troff macros not appearing in groff  
4.3.7.2 groff macros not appearing in AT&T troff  

4.3.7.1 troff macros not appearing in groff

Macros missing from groff -ms are cover page macros specific to Bell Labs. The macros known to be missing are:

.TM
Technical memorandum; a cover sheet style

.IM
Internal memorandum; a cover sheet style

.MR
Memo for record; a cover sheet style

.MF
Memo for file; a cover sheet style

.EG
Engineer's notes; a cover sheet style

.TR
Computing Science Tech Report; a cover sheet style

.OK
Other keywords

.CS
Cover sheet information

.MH
A cover sheet macro

4.3.7.2 groff macros not appearing in AT&T troff

The groff -ms macros have a few minor extensions compared to the AT&T troff -ms macros.

Macro: .AM
Improved accent marks. See section 4.3.6.5 Strings and Special Characters, for details.

Macro: .DS I
Indented display. The default behavior of AT&T troff -ms was to indent; the groff default prints displays flush left with the body text.

Macro: .CW
Print text in constant width (Courier) font.

Macro: .IX
Indexing term (printed on standard error). You can write a script to capture and process an index generated in this manner.

The following additional number registers appear in groff -ms:

Register: \n[MINGW]
Specifies a minimum space between columns (for multi-column output); this takes the place of the GW register that was documented but apparently not implemented in AT&T troff.

Several new string registers are available as well. You can change these to handle (for example) the local language. See section 4.3.6.5 Strings and Special Characters, for details.

4.4 `me'

See the `meintro.me' and `meref.me' documents in groff's `doc' directory.

4.5 `mm'

See the groff_mm(7) man page (type man groff_mm at the command line).

5. gtroff Reference

This chapter covers all of the facilities of gtroff. Users of macro packages may skip it if not interested in details.

5.1 Text  
5.2 Input Conventions  
5.3 Measurements  
5.4 Expressions  
5.5 Identifiers  
5.6 Embedded Commands  
5.7 Registers  
5.8 Manipulating Filling and Adjusting  
5.9 Manipulating Hyphenation  
5.10 Manipulating Spacing  
5.11 Tabs and Fields  
5.12 Character Translations  
5.13 Troff and Nroff Mode  
5.14 Line Layout  
5.15 Line Control  
5.16 Page Layout  
5.17 Page Control  
5.18 Fonts  
5.19 Sizes  
5.20 Strings  
5.21 Conditionals and Loops  
5.22 Writing Macros  
5.23 Page Motions  
5.24 Drawing Requests  
5.25 Traps  
5.26 Diversions  
5.27 Environments  
5.28 Suppressing output  
5.29 Colors  
5.30 I/O  
5.31 Postprocessor Access  
5.32 Miscellaneous  
5.33 gtroff Internals  
5.34 Debugging  
5.35 Implementation Differences  

5.1 Text

gtroff input files contain text with control commands interspersed throughout. But, even without control codes, gtroff still does several things with the input text:

5.1.1 Filling and Adjusting  
5.1.2 Hyphenation  
5.1.3 Sentences  
5.1.4 Tab Stops  
5.1.5 Implicit Line Breaks  

5.1.1 Filling and Adjusting

When gtroff reads text, it collects words from the input and fits as many of them together on one output line as it can. This is known as filling.

Once gtroff has a filled line, it tries to adjust it. This means it widens the spacing between words until the text reaches the right margin (in the default adjustment mode). Extra spaces between words are preserved, but spaces at the end of lines are ignored. Spaces at the front of a line cause a break (breaks are explained in 5.1.5 Implicit Line Breaks).

See section 5.8 Manipulating Filling and Adjusting.

5.1.2 Hyphenation

Since the odds are not great for finding a set of words, for every output line, which fit nicely on a line without inserting excessive amounts of space between words, gtroff hyphenates words so that it can justify lines without inserting too much space between words. It uses an internal hyphenation algorithm (a simplified version of the algorithm used within TeX) to indicate which words can be hyphenated and how to do so. When a word is hyphenated, the first part of the word is added to the current filled line being output (with an attached hyphen), and the other portion is added to the next line to be filled.

See section 5.9 Manipulating Hyphenation.

5.1.3 Sentences

Although it is often debated, some typesetting rules say there should be different amounts of space after various punctuation marks. For example, the Chicago typsetting manual says that a period at the end of a sentence should have twice as much space following it as would a comma or a period as part of an abbreviation.

gtroff does this by flagging certain characters (normally `!', `?', and `.') as end-of-sentence characters. When gtroff encounters one of these characters at the end of a line, it appends a normal space followed by a sentence space in the formatted output. (This justifies one of the conventions mentioned in 5.2 Input Conventions.)

In addition, the following characters and symbols are treated transparently while handling end-of-sentence characters: `"', `'', `)', `]', `*', \[dg], and \[rq].

See the cflags request in 5.18.4 Using Symbols, for more details.

To prevent the insertion of extra space after an end-of-sentence character (at the end of a line), append \&.

5.1.4 Tab Stops

gtroff translates tabulator characters, also called tabs (normally code point ASCII 0x09 or EBCDIC 0x05), in the input into movements to the next tabulator stop. These tab stops are initially located every half inch across the page. Using this, simple tables can be made easily. However, it can often be deceptive as the appearance (and width) of the text on a terminal and the results from gtroff can vary greatly.

Also, a possible sticking point is that lines beginning with tab characters are still filled, again producing unexpected results. For example, the following input

1 2 3
4 5

produces

1 2 3 4 5

See section 5.11 Tabs and Fields.

5.1.5 Implicit Line Breaks

An important concept in gtroff is the break. When a break occurs, gtroff outputs the partially filled line (unjustified), and resumes collecting and filling text on the next output line.

There are several ways to cause a break in gtroff. A blank line not only causes a break, but it also outputs a one-line vertical space (effectively a blank line). Note that this behaviour can be modified with the blank line macro request blm. See section 5.25.4 Blank Line Traps.

A line that begins with a space causes a break and the space is output at the beginning of the next line. Note that this space isn't adjusted, even in fill mode.

The end of file also causes a break -- otherwise the last line of the document may vanish!

Certain requests also cause breaks, implicitly or explicitly. This is discussed in 5.8 Manipulating Filling and Adjusting.

5.2 Input Conventions

Since gtroff does filling automatically, it is traditional in groff not to try and type things in as nicely formatted paragraphs. These are some conventions commonly used when typing gtroff text:

5.3 Measurements

gtroff (like many other programs) requires numeric parameters to specify various measurements. Most numeric parameters@footnotegroff_82.html{those that specify vertical or horizontal motion or a type size may have a measurement unit attached. These units are specified as a single character which immediately follows the number or expression. Each of these units are understood, by gtroff, to be a multiple of its basic unit. So, whenever a different measurement unit is specified gtroff converts this into its basic units. This basic unit, represented by a `u', is a device dependent measurement which is quite small, ranging from 1/75th to 1/72000th of an inch. The values may be given as fractional numbers; however, fractional basic units are always rounded to integers.

Some of the measurement units are completely independent of any of the current settings (e.g. type size) of gtroff.

i
Inches. An antiquated measurement unit still in use in certain backwards countries with incredibly low-cost computer equipment. One inch is equal to 2.54cm.

c
Centimeters. One centimeter is equal to 0.3937in.

p
Points. This is a typesetter's measurement used for measure type size. It is 72 points to an inch.

P
Pica. Another typesetting measurement. 6 Picas to an inch (and 12 points to a pica).

s
z
See section 5.19.2 Fractional Type Sizes, for a discussion of these units.

f
Fractions. Value is 65536. See section 5.29 Colors, for usage.

The other measurements understood by gtroff depend on settings currently in effect in gtroff. These are very useful for specifying measurements which should look proper with any size of text.

m
Ems. This unit is equal to the current font size in points. So called because it is approximately the width of the letter `m' in the current font.

n
Ens. In groff, this is half of an em.

v
Vertical space. This is equivalent to the current line spacing. See section 5.19 Sizes, for more information about this.

M
100ths of an em.

5.3.1 Default Units  

5.3.1 Default Units

Many requests take a default unit. While this can be helpful at times, it can cause strange errors in some expressions. For example, the line length request expects em units. Here are several attempts to get a line length of 3.5 inches and their results:

 
3.5i      =>   3.5i
7/2       =>   0i
7/2i      =>   0i
(7 / 2)u  =>   0i
7i/2      =>   0.1i
7i/2u     =>   3.5i

Everything is converted to basic units first. In the above example it is assumed that 1i equals 240u, and 1m equals 10p (thus 1m equals 33u). The value 7i/2 is first handled as 7i/2m, then converted to 1680u/66u which is 25u, and this is approximately 0.1i. As can be seen, a scaling indicator after a closing parenthesis is simply ignored.

Thus, the safest way to specify measurements is to always attach a scaling indicator. If you want to multiply or divide by a certain scalar value, use `u' as the unit for that value.

5.4 Expressions

gtroff has most arithmetic operators common to other languages:

Parentheses may be used as in any other language. However, in gtroff they are necessary to ensure order of evaluation. gtroff has no operator precedence; expressions are evaluated left to right. This means that gtroff evaluates `3+5*4' as if it were parenthesized like `(3+5)*4', not as `3+(5*4)', as might be expected.

For many requests which cause a motion on the page, the unary operators `+' and `-' work differently if leading an expression. They then indicate a motion relative to the current position (down or up, respectively).

Similarly, a leading `|' operator indicates an absolute position. For vertical movements, it specifies the distance from the top of the page; for horizontal movements, it gives the distance from the beginning of the input line.

`+' and `-' are also treated differently by the following requests and escapes: bp, in, ll, lt, nm, nr, pl, pn, po, ps, pvs, rt, ti, \H, \R, and \s. Here, leading plus and minus signs indicate increments and decrements.

See section 5.7.1 Setting Registers, for some examples.

Escape: \B'anything'
Return 1 if anything is a valid numeric expression; or 0 if anything is empty or not a valid numeric expression.

Due to the way arguments are parsed, spaces are not allowed in expressions, unless the entire expression is surrounded by parentheses.

See section 5.6.1.1 Request Arguments, and 5.21 Conditionals and Loops.

5.5 Identifiers

Like any other language, gtroff has rules for properly formed identifiers. In gtroff, an identifier can be made up of almost any printable character, with the exception of the following characters:

For example, any of the following is valid.

 
br
PP
(l
end-list
@_

Note that identifiers longer than two characters with a closing bracket (`]') in its name can't be accessed with escape sequences which expect an identifier as a parameter. For example, `\[foo]]' accesses the glyph `foo', followed by `]', whereas `\C'foo]'' really asks for glyph `foo]'.

To avoid problems with the refer preprocessor, macro names should not start with `[' or `]'. Due to backwards compatibility, everything after `.[' and `.]' is handled as a special argument to refer. For example, `.[foo' makes refer to start a reference, using `foo' as a parameter.

Escape: \A'ident'
Test whether an identifier ident is valid in gtroff. It expands to the character 1 or 0 according to whether its argument (usually delimited by quotes) is or is not acceptable as the name of a string, macro, diversion, number register, environment, or font. It returns 0 if no argument is given. This is useful for looking up user input in some sort of associative table.

 
\A'end-list'
    => 1

See section 5.6.3 Escapes, for details on parameter delimiting characters.

Identifiers in gtroff can be any length, but, in some contexts, gtroff needs to be told where identifiers end and text begins (and in different ways depending on their length):

Unlike many other programming languages, undefined identifiers are silently ignored or expanded to nothing. When gtroff finds an undefined identifier, it emits a warning, doing the following:

See section 5.34.1 Warnings., 5.7.2 Interpolating Registers, and 5.20 Strings.

Note that macros, strings, and diversions share the same name space.

 
.de xxx
.  nop foo
..
.
.di xxx
bar
.br
.di
.
.xxx
    => bar

As can be seen in the previous example, gtroff reuses the identifier `xxx', changing it from a macro to a diversion. No warning is emitted! The contents of the first macro definition is lost.

See section 5.7.2 Interpolating Registers, and 5.20 Strings.

5.6 Embedded Commands

Most documents need more functionality beyond filling, adjusting and implicit line breaking. In order to gain further functionality, gtroff allows commands to be embedded into the text, in two ways.

The first is a request which takes up an entire line, and does some large-scale operation (e.g. break lines, start new pages).

The other is an escape which can be usually embedded anywhere in the text; most requests can accept it even as an argument. Escapes generally do more minor operations like sub- and superscripts, print a symbol, etc.

5.6.1 Requests  
5.6.2 Macros  
5.6.3 Escapes  

5.6.1 Requests

A request line begins with a control character, which is either a single quote (`'', the no-break control character) or a period (`.', the normal control character). These can be changed; see 5.12 Character Translations, for details. After this there may be optional tabs or spaces followed by an identifier which is the name of the request. This may be followed by any number of space-separated arguments (no tabs here).

Since a control character followed by whitespace only is ignored, it is common practice to use this feature for structuring the source code of documents or macro packages.

 
.de foo
.  tm This is foo.
..
.
.
.de bar
.  tm This is bar.
..

Another possibility is to use the blank line macro request blm by assigning an empty macro to it.

 
.de do-nothing
..
.blm do-nothing  \" activate blank line macro

.de foo
.  tm This is foo.
..


.de bar
.  tm This is bar.
..

.blm             \" deactivate blank line macro

See section 5.25.4 Blank Line Traps.

To begin a line with a control character without it being interpreted, precede it with \&. This represents a zero width space, which means it does not affect the output.

In most cases the period is used as a control character. Several requests cause a break implicitly; using the single quote control character prevents this.

5.6.1.1 Request Arguments  

5.6.1.1 Request Arguments

Arguments to requests (and macros) are processed much like the shell: The line is split into arguments according to spaces.@footnotegroff_88.html{Plan 9's troff implementation also allows tabs for argument separation -- gtroff intentionally doesn't support this. An argument which is intended to contain spaces can either be enclosed in double quotes, or have the spaces escaped with backslashes.

Here are a few examples:

 
.uh The Mouse Problem
.uh "The Mouse Problem"
.uh The\ Mouse\ Problem

The first line is the uh macro being called with 3 arguments, `The', `Mouse', and `Problem'. The latter two have the same effect of calling the uh macro with one argument, `The Mouse Problem.@footnotegroff_88.html{The last solution, i.e., using escaped spaces, is "classical" in the sense that it can be found in most troff documents. Nevertheless, it is not optimal in all situations, since `\ ' inserts a fixed-width, non-breaking space character which can't stretch. gtroff provides a different command \~ to insert a stretchable, non-breaking space.

A double quote which isn't preceded by a space doesn't start a macro argument. If not closing a string, it is printed literally.

For example,

 
.xxx a" "b c" "de"fg"

has the arguments `a"', `b c', `de', and `fg"'. Don't rely on this obscure behaviour!

There are two possibilities to get a double quote reliably.

Double quotes in the ds request are handled differently. See section 5.20 Strings, for more details.

5.6.2 Macros

gtroff has a macro facility for defining a series of lines which can be invoked by name. They are called in the same manner as requests -- arguments also may be passed in the same manner.

See section 5.22 Writing Macros, and 5.6.1.1 Request Arguments.

5.6.3 Escapes

Escapes may occur anywhere in the input to gtroff. They usually begin with a backslash and are followed by a single character which indicates the function to be performed. The escape character can be changed; see 5.12 Character Translations.

Escape sequences which require an identifier as a parameter accept three possible syntax forms.

Examples:

 
\fB
\n(XX
\*[TeX]

Other escapes may require several arguments and/or some special format. In such cases the argument is traditionally enclosed in single quotes (and quotes are always used in this manual for the definitions of escape sequences). The enclosed text is then processed according to what that escape expects. Example:

 
\l'1.5i\(bu'

Note that the quote character can be replaced with any other character which does not occur in the argument (even a newline or a space character) in the following escapes: \o, \b, and \X. This makes e.g.

 
A caf
\o
e\'


in Paris
  => A café in Paris

possible, but it is better not to use this feature to avoid confusion.

The following escapes sequences (which are handled similarly to characters since they don't take a parameter) are also allowed as delimiters: \%, `\ ', \|, \^, \{, \}, \', \`, \-, \_, \!, \?, \@, \), \/, \,, \&, \:, \~, \0, \a, \c, \d, \e, \E, \p, \r, \t, and \u. Again, don't use these if possible.

No newline characters as delimiters are allowed in the following escapes: \A, \B, \Z, \C, and \w.

Finally, the escapes \D, \h, \H, \l, \L, \N, \R, \s, \S, \v, and \x can't use the following characters as delimiters:

To have a backslash (actually, the current escape character) appear in the output several escapes are defined: \\, \e or \E. These are very similar, and only differ with respect to being used in macros or diversions. See section 5.12 Character Translations, for an exact description of those escapes.

See section 5.35 Implementation Differences, 5.22.1 Copy-in Mode, and 5.26 Diversions, 5.5 Identifiers, for more information.

5.6.3.1 Comments  

5.6.3.1 Comments

Probably one of the most@footnotegroff_91.html{Unfortunately, this is a lie. But hopefully future gtroff hackers will believe it :-) common forms of escapes is the comment.

Escape: \"\delimI\\arg\\delimII\
Start a comment. Everything to the end of the input line is ignored.

This may sound simple, but it can be tricky to keep the comments from interfering with the appearance of the final output.

If the escape is to the right of some text or a request, that portion of the line is ignored, but the space leading up to it is noticed by gtroff. This only affects the ds and as request and its variants.

One possibly irritating idiosyncracy is that tabs must not be used to line up comments. Tabs are not treated as whitespace between the request and macro arguments.

A comment on a line by itself is treated as a blank line, because after eliminating the comment, that is all that remains:

 
Test
\" comment
Test

produces

 
Test

Test

To avoid this, it is common to start the line with .\" which causes the line to be treated as an undefined request and thus ignored completely.

Another commenting scheme seen sometimes is three consecutive single quotes ("') at the beginning of a line. This works, but gtroff gives a warning about an undefined macro (namely "), which is harmless, but irritating.

Escape: \#\delimI\\arg\\delimII\
To avoid all this, gtroff has a new comment mechanism using the \# escape. This escape works the same as \" except that the newline is also ignored:

 
Test
\# comment
Test

produces

 
Test Test

as expected.

Request: .ig yy
Ignore all input until gtroff encounters the macro named .yy on a line by itself (or .. if yy is not specified). This is useful for commenting out large blocks of text:

 
text text text...
.ig
This is part of a large block
of text that has been
temporarily(?) commented out.

We can restore it simply by removing
the .ig request and the ".." at the
end of the block.
..
More text text text...

produces

 
text text text...  More text text text...

Note that the commented-out block of text does not cause a break.

The input is read in copy-mode; auto-incremented registers are affected (see section 5.7.3 Auto-increment).

5.7 Registers

Numeric variables in gtroff are called registers. There are a number of built-in registers, supplying anything from the date to details of formatting parameters.

See section 5.5 Identifiers, for details on register identifiers.

5.7.1 Setting Registers  
5.7.2 Interpolating Registers  
5.7.3 Auto-increment  
5.7.4 Assigning Formats  
5.7.5 Built-in Registers  

5.7.1 Setting Registers

Define or set registers using the nr request or the \R escape.

Request: .nr ident value
Escape: \R'ident value'
Set number register ident to value. If ident doesn't exist, gtroff creates it.

The argument to \R usually has to be enclosed in quotes. See section 5.6.3 Escapes, for details on parameter delimiting characters.

The \R escape doesn't produce an input token in gtroff; with other words, it vanishes completely after gtroff has processed it.

For example, the following two lines are equivalent:

 
.nr a (((17 + (3 * 4))) % 4)
\R'a (((17 + (3 * 4))) % 4)'
    => 1

Both nr and \R have two additional special forms to increment or decrement a register.

Request: .nr ident +
Request: .nr ident -
Escape: \R'ident +\delimII\
Escape: \R'ident -\delimII\
Increment (decrement) register ident by value.

 
.nr a 1
.nr a +1
\na
    => 2

To assign the negated value of a register to another register, some care must be taken to get the desired result:

 
.nr a 7
.nr b 3
.nr a -\nb
\na
    => 4
.nr a (-\nb)
\na
    => -3

The surrounding parentheses prevent the interpretation of the minus sign as a decrementing operator. An alternative is to start the assignment with a `0':

 
.nr a 7
.nr b -3
.nr a \nb
\na
    => 4
.nr a 0\nb
\na
    => -3

Request: .rr ident
Remove number register ident. If ident doesn't exist, the request is ignored.

Request: .rnn ident1 ident2
Rename number register ident1 to ident2. If either ident1 or ident2 doesn't exist, the request is ignored.

Request: .aln ident1 ident2
Create an alias ident1 for a number register ident2. The new name and the old name are exactly equivalent. If ident1 is undefined, a warning of type `reg' is generated, and the request is ignored. See section 5.34 Debugging, for information about warnings.

5.7.2 Interpolating Registers

Numeric registers can be accessed via the \n escape.

Escape: \ni\delimII\
Escape: \n(\arg\\delimII\
Escape: \n[\arg\\delimII\
Interpolate number register with name ident (one-character name i, two-character name id). This means that the value of the register is expanded in-place while gtroff is parsing the input line. Nested assignments (also called indirect assignments) are possible.

 
.nr a 5
.nr as \na+\na
\n(as
    => 10

 
.nr a1 5
.nr ab 6
.ds str b
.ds num 1
\n[a\n[num]]
    => 5
\n[a\*[str]]
    => 6

5.7.3 Auto-increment

Number registers can also be auto-incremented and auto-decremented. The increment or decrement value can be specified with a third argument to the nr request or \R escape.

Request: .nr ident value incr
Set number register ident to value; the increment for auto-incrementing is set to incr. Note that the \R escape doesn't support this notation.

To activate auto-incrementing, the escape \n has a special syntax form.

Escape: \n+i\delimII\
Escape: \n-i\delimII\
Escape: \n(\arg\\delimII\
Escape: \n(\arg\\delimII\
Escape: \n+(\arg\\delimII\
Escape: \n-(\arg\\delimII\
Escape: \n[\arg\\delimII\
Escape: \n[\arg\\delimII\
Escape: \n+[\arg\\delimII\
Escape: \n-[\arg\\delimII\
Before interpolating, increment or decrement ident (one-character name i, two-character name id) by the auto-increment value as specified with the nr request (or the \R escape). If no auto-increment value has been specified, these syntax forms are identical to \n.

For example,

 
.nr a 0 1
.nr xx 0 5
.nr foo 0 -2
\n+a, \n+a, \n+a, \n+a, \n+a
.br
\n-(xx, \n-(xx, \n-(xx, \n-(xx, \n-(xx
.br
\n+[foo], \n+[foo], \n+[foo], \n+[foo], \n+[foo]

produces

 
1, 2, 3, 4, 5
-5, -10, -15, -20, -25
-2, -4, -6, -8, -10

To change the increment value without changing the value of a register (a in the example), the following can be used:

 
.nr a \na 10

5.7.4 Assigning Formats

When a register is used in the text of an input file (as opposed to part of an expression), it is textually replaced (or interpolated) with a representation of that number. This output format can be changed to a variety of formats (numbers, Roman numerals, etc.). This is done using the af request.

Request: .af ident format
Change the output format of a number register. The first argument ident is the name of the number register to be changed, and the second argument format is the output format. The following output formats are available:

1
Decimal arabic numbers. This is the default format: 0, 1, 2, 3, '....

0...0
Decimal numbers with as many digits as specified. So, `00' would result in printing numbers as 01, 02, 03, ....

In fact, any digit instead of zero will do; gtroff only counts how many digits are specified. As a consequence, af's default format `1' could be specified as `0' also (and exactly this is returned by the \g escape, see below).

I
Upper-case Roman numerals: 0, I, II, III, IV, ....

i
Lower-case Roman numerals: 0, i, ii, iii, iv, ....

A
Upper-case letters: 0, A, B, C, ..., Z, AA, AB, ....

a
Lower-case letters: 0, a, b, c, ..., z, aa, ab, ....

Omitting the number register format causes a warning of type `missing'. See section 5.34 Debugging, for more details. Specifying a nonexistent format causes an error.

The following example produces `10, X, j, 010':

 
.nr a 10
.af a 1           \" the default format
\na,
.af a I
\na,
.af a a
\na,
.af a 001
\na

The largest number representable for the `i' and `I' formats is 39999 (or -39999); UNIX troff uses `z' and `w' to represent 10000 and 5000 in Roman numerals, and so does gtroff. Currently, the correct glyphs of Roman numeral five thousand and Roman numeral ten thousand (Unicode code points U+2182 and U+2181, respectively) are not available.

If ident doesn't exist, it is created.

Changing the output format of a read-only register causes an error. It is necessary to first copy the register's value to a writeable register, then apply the af request to this other register.

Escape: \gi\delimII\
Escape: \g(\arg\\delimII\
Escape: \g[\arg\\delimII\
Return the current format of the specified register ident (one-character name i, two-character name id). For example, `\ga' after the previous example would produce the string `000'. If the register hasn't been defined yet, nothing is returned.

5.7.5 Built-in Registers

The following lists some built-in registers which are not described elsewhere in this manual. Any register which begins with a `.' is read-only. A complete listing of all built-in registers can be found in appendix E. Register Index.

.F
This string-valued register returns the current input file name.

.H
Horizontal resolution in basic units.

.V
Vertical resolution in basic units.

seconds
The number of seconds after the minute, normally in the range 0 to 59, but can be up to 61 to allow for leap seconds. Initialized at start-up of gtroff.

minutes
The number of minutes after the hour, in the range 0 to 59. Initialized at start-up of gtroff.

hours
The number of hours past midnight, in the range 0 to 23. Initialized at start-up of gtroff.

dw
Day of the week (1-7).

dy
Day of the month (1-31).

mo
Current month (1-12).

year
The current year.

yr
The current year minus 1900. Unfortunately, the documentation of UNIX Version 7's troff had a year 2000 bug: It incorrectly claimed that yr contains the last two digits of the year. That claim has never been true of either AT&T troff or GNU troff. Old troff input that looks like this:

 
'\" The following line stopped working after 1999
This document was formatted in 19\n(yr.

can be corrected as follows:

 
This document was formatted in \n[year].

or, to be portable to older troff versions, as follows:

 
.nr y4 1900+\n(yr
This document was formatted in \n(y4.

.c
c.
The current input line number. Register `.c' is read-only, whereas `c.' (a gtroff extension) is writable also, affecting both `.c' and `c.'.

ln
The current output line number after a call to the nm request to activate line numbering.

See section 5.32 Miscellaneous, for more information about line numbering.

.x
The major version number. For example, if the version number is 1.03 then .x contains `1'.

.y
The minor version number. For example, if the version number is 1.03 then .y contains `03'.

.Y
The revision number of groff.

$$
The process ID of gtroff.

.g
Always 1. Macros should use this to determine whether they are running under GNU troff.

.A
If the command line option `-a' is used to produce an ASCII approximation of the output, this is set to 1, zero otherwise. See section 2.1 Options.

.P
This register is set to 1 (and to 0 otherwise) if the current page is actually being printed, i.e., if the `-o' option is being used to only print selected pages. See section 2.1 Options, for more information.

.T
If gtroff is called with the `-T' command line option, the number register .T is set to 1, and zero otherwise. See section 2.1 Options.

Additionally, gtroff predefines a single read-write string register .T which contains the current output device (for example, `latin1' or `ps').

5.8 Manipulating Filling and Adjusting

Various ways of causing breaks were given in 5.1.5 Implicit Line Breaks. The br request likewise causes a break. Several other requests also cause breaks, but implicitly. These are bp, ce, cf, fi, fl, in, nf, rj, sp, ti, and trf.

Request: .br \arg\
Break the current line, i.e., the input collected so far is emitted without adjustment.

If the no-break control character is used, gtroff suppresses the break:

 
a
'br
b
    => a b

Initially, gtroff fills and adjusts text to both margins. Filling can be disabled via the nf request and re-enabled with the fi request.

Request: .fi \arg\
Register: \n[.u]
Activate fill mode (which is the default). This request implicitly enables adjusting; it also inserts a break in the text currently being filled. The read-only number register .u is set to 1.

The fill mode status is associated with the current environment (see section 5.27 Environments).

See 5.15 Line Control, for interaction with the \c escape.

Request: .nf \arg\
Activate no-fill mode. Input lines are output as-is, retaining line breaks and ignoring the current line length. This command implicitly disables adjusting; it also causes a break. The number register .u is set to 0.

The fill mode status is associated with the current environment (see section 5.27 Environments).

See 5.15 Line Control, for interaction with the \c escape.

Request: .ad [{mode
Register: \n[.j]
Set adjusting mode.

Activation and deactivation of adjusting is done implicitly with calls to the fi or nf requests.

mode can have one of the following values:

l
Adjust text to the left margin. This produces what is traditionally called ragged-right text.

r
Adjust text to the right margin, producing ragged-left text.

c
Center filled text. This is different to the ce request which only centers text without filling.

b
n
Justify to both margins. This is the default used by gtroff.

With no argument, gtroff adjusts lines in the same way it did before adjusting was deactivated (with a call to na, for example).

 
text
.ad r
text
.ad c
text
.na
text
.ad  \" back to centering
text

The current adjustment mode is available in the read-only number register .j; it can be stored and subsequently used to set adjustment.

The adjustment mode status is associated with the current environment (see section 5.27 Environments).

Request: .na \arg\
Disable adjusting. This request won't change the current adjustment mode: A subsequent call to ad uses the previous adjustment setting.

The adjustment mode status is associated with the current environment (see section 5.27 Environments).

Request: .brp \arg\
Escape: \p\delimI\\arg\\delimII\
Adjust the current line and cause a break.

In most cases this produces very ugly results since gtroff doesn't have a sophisticated paragraph building algorithm (as TeX have, for example); instead, gtroff fills and adjusts a paragraph line by line:

 
  This is an uninteresting sentence.
  This is an uninteresting sentence.\p
  This is an uninteresting sentence.

is formatted as

 
  This is  an uninteresting  sentence.   This  is an
  uninteresting                            sentence.
  This is an uninteresting sentence.

Request: .ss word_space_size [{sentence_space_size
Register: \n[.ss]
Register: \n[.sss]
Change the minimum size of a space between filled words. It takes its units as one twelfth of the space width parameter for the current font. Initially both the word_space_size and sentence_space_size are 12.

If two arguments are given to the ss request, the second argument sets the sentence space size. If the second argument is not given, sentence space size is set to word_space_size. The sentence space size is used in two circumstances: If the end of a sentence occurs at the end of a line in fill mode, then both an inter-word space and a sentence space are added; if two spaces follow the end of a sentence in the middle of a line, then the second space is a sentence space. If a second argument is never given to the ss request, the behaviour of UNIX troff is the same as that exhibited by GNU troff. In GNU troff, as in UNIX troff, a sentence should always be followed by either a newline or two spaces.

The read-only number registers .ss and .sss hold the values of the parameters set by the first and second arguments of the ss request.

The word space and sentence space values are associated with the current environment (see section 5.27 Environments).

Contrary to AT&T troff, this request is not ignored if a TTY output device is used; the given values are then rounded down to a multiple of 12 (see section 5.35 Implementation Differences).

The request is ignored if there is no parameter.

Request: .ce [{nnn
Register: \n[.ce]
Center text. While the `.ad c' request also centers text, it fills the text as well. ce does not fill the text it affects. This request causes a break. The number of lines still to be centered is associated with the current environment (see section 5.27 Environments).

The following example demonstrates the differences. Here the input:

 
.ll 4i
.ce 1000
This is a small text fragment which shows the differences
between the `.ce' and the `.ad c' request.
.ce 0

.ad c
This is a small text fragment which shows the differences
between the `.ce' and the `.ad c' request.

And here the result:

 
  This is a small text fragment which
         shows the differences
between the `.ce' and the `.ad c' request.

  This is a small text fragment which
shows the differences between the `.ce'
        and the `.ad c' request.

With no arguments, ce centers the next line of text. nnn specifies the number of lines to be centered. If the argument is zero or negative, centering is disabled.

The basic length for centering text is the line length (as set with the ll request) minus the indentation (as set with the in request). Temporary indentation is ignored.

As can be seen in the previous example, it is a common idiom to turn on centering for a large number of lines, and to turn off centering after text to be centered. This is useful for any request which takes a number of lines as an argument.

The .ce read-only number register contains the number of lines remaining to be centered, as set by the ce request.

Request: .rj [{nnn
Register: \n[.rj]
Justify unfilled text to the right margin. Arguments are identical to the ce request. The .rj read-only number register is the number of lines to be right-justified as set by the rj request. This request causes a break. The number of lines still to be right-justified is associated with the current environment (see section 5.27 Environments).

5.9 Manipulating Hyphenation

As discussed in 5.1.2 Hyphenation, gtroff hyphenates words. There are a number of ways to influence hyphenation.

Request: .hy [{mode
Register: \n[.hy]
Enable hyphenation. The request has an optional numeric argument, mode, to restrict hyphenation if necessary:

1
The default argument if mode is omitted. Hyphenate without restrictions. This is also the start-up value of gtroff.

2
Do not hyphenate the last word on a page or column.

4
Do not hyphenate the last two characters of a word.

8
Do not hyphenate the first two characters of a word.

Values in the previous table are additive. For example, the value 12 causes gtroff to neither hyphenate the last two nor the first two characters of a word.

The current hyphenation restrictions can be found in the read-only number register `.hy'.

The hyphenation mode is associated with the current environment (see section 5.27 Environments).

Request: .nh \arg\
Disable hyphenation (i.e., set the hyphenation mode to zero). Note that the hyphenation mode of the last call to hy is not remembered.

The hyphenation mode is associated with the current environment (see section 5.27 Environments).

Request: .hlm [{nnn
Register: \n[.hlm]
Register: \n[.hlc]
Set the maximum number of consecutive hyphenated lines to nnn. If this number is negative, there is no maximum. The default value is -1 if nnn is omitted. This value is associated with the current environment (see section 5.27 Environments). Only lines output from a given environment count towards the maximum associated with that environment. Hyphens resulting from \% are counted; explicit hyphens are not.

The current setting of hlm is available in the .hlm read-only number register. Also the number of immediately preceding consecutive hyphenated lines are available in the read-only number register `.hlc'.

Request: .hw word1 word2 @dots{
Define how word1, word2, etc. are to be hyphenated. The words must be given with hyphens at the hyphenation points. For example:

 
.hw in-sa-lub-rious

Besides the space character, any character whose hyphenation code value is zero can be used to separate the arguments of hw (see the documentation for the hcode request below for more information). In addition, this request can be used more than once.

Hyphenation exceptions specified with the hw request are associated with the current hyphenation language; it causes an error if there is no current hyphenation language.

This request is ignored if there is no parameter.

In old versions of troff there was a limited amount of space to store such information; fortunately, with gtroff, this is no longer a restriction.

Escape: \%\delimI\\arg\\delimII\
Escape: \:
To tell gtroff how to hyphenate words on the fly, use the \% escape, also known as the hyphenation character. Preceding a word with this character prevents it from being hyphenated; putting it inside a word indicates to gtroff that the word may be hyphenated at that point. Note that this mechanism only affects that one occurrence of the word; to change the hyphenation of a word for the entire document, use the hw request.

The \: escape inserts a zero-width break point (that is, the word breaks but without adding a hyphen).

 
... check the /var/log/\:httpd/\:access_log file ...

Note that \X and \Y start a word, that is, the \% escape in (say) ` \X'...'\%foobar' and ` \Y'...'\%foobar' no longer prevents hyphenation but inserts a hyphenation point at the beginning of `foobar'; most likely this isn't what you want to do.

Request: .hc [{char
Change the hyphenation character to char. This character then works the same as the \% escape, and thus, no longer appears in the output. Without an argument, hc resets the hyphenation character to be \% (the default) only.

The hyphenation character is associated with the current environment (see section 5.27 Environments).

Request: .hpf pattern_file
Request: .hpfa pattern_file
Request: .hpfcode a b [c d @dots{
Read in a file of hyphenation patterns. This file is searched for in the same way as `name.tmac' (or `tmac.name') is searched for if the `-mname' option is specified.

It should have the same format as (simple) TeX patterns files. More specifically, the following scanning rules are implemented.

  • A percent sign starts a comment (up to the end of the line) even if preceded by a backslash.

  • No support for `digraphs' like \$.

  • ^^xx (x is 0-9 or a-f) and ^^x (character code of x in the range 0-127) are recognized; other use of ^ causes an error.

  • No macro expansion.

  • hpf checks for the expression \patterns{...} (possibly with whitespace before and after the braces). Everything between the braces is taken as hyphenation patterns. Consequently, { and } are not allowed in patterns.

  • Similarly, \hyphenation{...} gives a list of hyphenation exceptions.

  • \endinput is recognized also.

  • For backwards compatibility, if \patterns is missing, the whole file is treated as a list of hyphenation patterns (only recognizing the % character as the start of a comment).

If no hpf request is specified (either in the document or in a macro package), gtroff won't hyphenate at all.

The hpfa request appends a file of patterns to the current list.

The hpfcode request defines mapping values for character codes in hyphenation patterns. hpf or hpfa then apply the mapping (after reading the patterns) before replacing or appending them to the current list of patterns. Its arguments are pairs of character codes -- integers from 0 to 255. The request maps character code a to code b, code c to code d, and so on. You can use character codes which would be invalid otherwise.

The set of hyphenation patterns is associated with the current language set by the hla request. The hpf request is usually invoked by the `troffrc' or `troffrc-end' file; by default, `troffrc' loads hyphenation patterns for American English (in file `hyphen.us').

A second call to hpf (for the same language) will replace the hyphenation patterns with the new ones.

Invoking hpf causes an error if there is no current hyphenation language.

Request: .hcode c1 code1 c2 code2 @dots{
Set the hyphenation code of character c1 to code1, that of c2 to code2, etc. A hyphenation code must be a single input character (not a special character) other than a digit or a space. Initially each lower-case letter (`a'-`z') has its hyphenation code set to itself, and each upper-case letter (`A'-`Z') has a hyphenation code which is the lower-case version of itself.

This request is ignored if it has no parameter.

Request: .hym [{length
Register: \n[.hym]
Set the (right) hyphenation margin to length. If the current adjustment mode is not `b' or `n', the line is not hyphenated if it is shorter than length. Without an argument, the hyphenation margin is reset to its default value, which is 0. The default scaling indicator for this request is `m'. The hyphenation margin is associated with the current environment (see section 5.27 Environments).

A negative argument resets the hyphenation margin to zero, emitting a warning of type `range'.

The current hyphenation margin is available in the .hym read-only number register.

Request: .hys [{hyphenation_space
Register: \n[.hys]
Set the hyphenation space to hyphenation_space. If the current adjustment mode is `b' or `n', don't hyphenate the line if it can be justified by adding no more than hyphenation_space extra space to each word space. Without argument, the hyphenation space is set to its default value, which is 0. The default scaling indicator for this request is `m'. The hyphenation space is associated with the current environment (see section 5.27 Environments).

A negative argument resets the hyphenation space to zero, emitting a warning of type `range'.

The current hyphenation space is available in the .hys read-only number register.

Request: .shc [{glyph
Set the soft hyphen character to glyph.@footnotegroff_99.html{@dfn{Soft hyphen character is a misnomer since it is an output glyph. If the argument is omitted, the soft hyphen character is set to the default glyph \(hy (this is the start-up value of gtroff also). The soft hyphen character is the glyph that is inserted when a word is hyphenated at a line break. If the soft hyphen character does not exist in the font of the character immediately preceding a potential break point, then the line is not broken at that point. Neither definitions (specified with the char request) nor translations (specified with the tr request) are considered when finding the soft hyphen character.

Request: .hla language
Register: \n[.hla]
Set the current hyphenation language to the string language. Hyphenation exceptions specified with the hw request and hyphenation patterns specified with the hpf and hpfa requests are both associated with the current hyphenation language. The hla request is usually invoked by the `troffrc' or the `troffrc-end' files; `troffrc' sets the default language to `us'.

The current hyphenation language is available as a string in the read-only number register `.hla'.

 
.ds curr_language \n[.hla]
\*[curr_language]
    => us

5.10 Manipulating Spacing

Request: .sp [{distance
Space downwards distance. With no argument it advances 1@w{ line. A negative argument causes gtroff to move up the page the specified distance. If the argument is preceded by a `|' then gtroff moves that distance from the top of the page. This request causes a line break. The default scaling indicator is `v'.

Request: .ls [{nnn
Register: \n[.L]
Output nnn-1 blank lines after each line of text. With no argument, gtroff uses the previous value before the last ls call.

 
.ls 2    \" This causes double-spaced output
.ls 3    \" This causes triple-spaced output
.ls      \" Again double-spaced

The line spacing is associated with the current environment (see section 5.27 Environments).

The read-only number register .L contains the current line spacing setting.

See section 5.19.1 Changing Type Sizes, for the requests vs and pvs as alternatives to ls.

Escape: \x'spacing'
Register: \n[.a]
Sometimes, extra vertical spacing is only needed occasionally, e.g. to allow space for a tall construct (like an equation). The \x escape does this. The escape is given a numerical argument, usually enclosed in quotes (like `\x'3p''); the default scaling indicator is `v'. If this number is positive extra vertical space is inserted below the current line. A negative number adds space above. If this escape is used multiple times on the same line, the maximum of the values is used.

See section 5.6.3 Escapes, for details on parameter delimiting characters.

The .a read-only number register contains the most recent (nonnegative) extra vertical line space.

Using \x can be necessary in combination with the \b escape, as the following example shows.

 
This is a test with the \[rs]b escape.
.br
This is a test with the \[rs]b escape.
.br
This is a test with \b'xyz'\x'-1m'\x'1m'.
.br
This is a test with the \[rs]b escape.
.br
This is a test with the \[rs]b escape.

produces

 
This is a test with the \b escape.
This is a test with the \b escape.
                    x
This is a test with y.
                    z
This is a test with the \b escape.
This is a test with the \b escape.

Request: .ns \arg\
Request: .rs \arg\
Register: \n[.ns]
Enable no-space mode. In this mode, spacing (either via sp or via blank lines) is disabled. The bp request to advance to the next page is also disabled, except if it is accompanied by a page number (see 5.17 Page Control, for more information). This mode ends when actual text is output or the rs request is encountered which ends no-space mode. The read-only number register .ns is set to 1 as long as no-space mode is active.

This request is useful for macros that conditionally insert vertical space before the text starts (for example, a paragraph macro could insert some space except when it is the first paragraph after a section header).

5.11 Tabs and Fields

A tab character (ASCII char 9, EBCDIC char@w{ 5) causes a horizontal movement to the next tab stop (much like it did on a typewriter).

Escape: \t\delimI\\arg\\delimII\
This escape is a non-interpreted tab character. In copy mode (see section 5.22.1 Copy-in Mode), \t is the same as a real tab character.

Request: .ta [{n1
Register: \n[.tabs]
Change tab stop positions. This request takes a series of tab specifiers as arguments (optionally divided into two groups with the letter `T') which indicate where each tab stop is to be (overriding any previous settings).

Tab stops can be specified absolutely, i.e., as the distance from the left margin. For example, the following sets 6 tab stops every one inch.

 
.ta 1i 2i 3i 4i 5i 6i

Tab stops can also be specified using a leading `+' which means that the specified tab stop is set relative to the previous tab stop. For example, the following is equivalent to the previous example.

 
.ta 1i +1i +1i +1i +1i +1i

gtroff supports an extended syntax to specify repeat values after the `T' mark (these values are always taken as relative) -- this is the usual way to specify tabs set at equal intervals. The following is, yet again, the same as the previous examples. It does even more since it defines an infinite number of tab stops separated by one inch.

 
.ta T 1i

Now we are ready to interpret the full syntax given at the beginning: Set tabs at positions n1, n2, ..., nn and then set tabs at nn+r1, nn+r2, ..., nn+rn and then at nn+rn+r1, nn+rn+r2, ..., nn+rn+rn, and so on.

Example: `4c +6c T 3c 5c 2c' is equivalent to @samp{4c 10c 13c 18c 20c 23c 28c 30c ....

The material in each tab column (i.e., the column between two tab stops) may be justified to the right or left or centered in the column. This is specified by appending `R', `L', or `C' to the tab specifier. The default justification is `L'. Example:

 
.ta 1i 2iC 3iR

Some notes:

  • The default unit of the ta request is `m'.

  • A tab stop is converted into a non-breakable horizontal movement which can be neither stretched nor squeezed. For example,

     
    .ds foo a\tb\tc
    .ta T 5i
    \*[foo]
    

    creates a single line which is a bit longer than 10 inches (a string is used to show exactly where the tab characters are). Now consider the following:

     
    .ds bar a\tb b\tc
    .ta T 5i
    \*[bar]
    

    gtroff first converts the tab stops of the line into unbreakable horizontal movements, then splits the line after the second `b' (assuming a sufficiently short line length). Usually, this isn't what the user wants.

  • Superfluous tabs (i.e., tab characters which do not correspond to a tab stop) are ignored except the first one which delimits the characters belonging to the last tab stop for right-justifying or centering. Consider the following example

     
    .ds Z   foo\tbar\tfoo
    .ds ZZ  foo\tbar\tfoobar
    .ds ZZZ foo\tbar\tfoo\tbar
    .ta 2i 4iR
    \*[Z]
    .br
    \*[ZZ]
    .br
    \*[ZZZ]
    .br
    

    which produces the following output:

     
    foo                 bar              foo
    foo                 bar           foobar
    foo                 bar              foobar
    

    The first line right-justifies the second `foo' relative to the tab stop. The second line right-justifies `foobar'. The third line finally right-justifies only `foo' because of the additional tab character which marks the end of the string belonging to the last defined tab stop.

  • Tab stops are associated with the current environment (see section 5.27 Environments).

  • Calling ta without an argument removes all tab stops.

  • The start-up value of gtroff is `T 0.5i' in troff mode and `T 0.8i' in nroff mode (the latter is done with an explicit call to the ta request in the file `tty.tmac'.

The read-only number register .tabs contains a string representation of the current tab settings suitable for use as an argument to the ta request.

 
.ds tab-string \n[.tabs]
\*[tab-string]
    => T120u

The troff version of the Plan 9 operating system uses register .S for the same purpose.

Request: .tc [{fill-glyph
Normally gtroff fills the space to the next tab stop with whitespace. This can be changed with the tc request. With no argument gtroff reverts to using whitespace, which is the default. The value of this tab repetition character is associated with the current environment (see section 5.27 Environments).@footnotegroff_101.html{Tab repetition character is a misnomer since it is an output glyph.

Request: .linetabs n
Register: \n[.linetabs]
If n is missing or not zero, enable line-tabs mode, or disable it otherwise (the default). In line-tabs mode, gtroff computes tab distances relative to the (current) output line instead of the input line.

For example, the following code:

 
.ds x a\t\c
.ds y b\t\c
.ds z c
.ta 1i 3i
\*x
\*y
\*z

in normal mode, results in the output

 
a         b         c

in line-tabs mode, the same code outputs

 
a         b                   c

Line-tabs mode is associated with the current environment. The read-only register .linetabs is set to 1 if in line-tabs mode, and 0 in normal mode.

5.11.1 Leaders  
5.11.2 Fields  

5.11.1 Leaders

Sometimes it may may be desirable to use the tc request to fill a particular tab stop with a given glyph (for example dots in a table of contents), but also normal tab stops on the rest of the line. For this gtroff provides an alternate tab mechanism, called leaders which does just that.

A leader character (character code 1) behaves similarly to a tab character: It moves to the next tab stop. The only difference is that for this movement, the fill glyph defaults to a period character and not to space.

Escape: \a\delimI\\arg\\delimII\
This escape is a non-interpreted leader character. In copy mode (see section 5.22.1 Copy-in Mode), \a is the same as a real leader character.

Request: .lc [{fill-glyph
Declare the leader repetition character.@footnotegroff_102.html{@dfn{Leader repetition character is a misnomer since it is an output glyph. Without an argument, leaders act the same as tabs (i.e., using whitespace for filling). gtroff's start-up value is a dot (`.'). The value of the leader repetition character is associated with the current environment (see section 5.27 Environments).

For a table of contents, to name an example, tab stops may be defined so that the section number is one tab stop, the title is the second with the remaining space being filled with a line of dots, and then the page number slightly separated from the dots.

 
.ds entry 1.1\tFoo\a\t12
.lc .
.ta 1i 5i +.25i
\*[entry]

This produces

 
1.1  Foo..........................................  12

5.11.2 Fields

Fields are a more general way of laying out tabular data. A field is defined as the data between a pair of delimiting characters. It contains substrings which are separated by padding characters. The width of a field is the distance on the input line from the position where the field starts to the next tab stop. A padding character inserts stretchable space similar to TeX's \hss command (thus it can even be negative) to make the sum of all substring lengths plus the stretchable space equal to the field width. If more than one padding character is inserted, the available space is evenly distributed among them.

Request: .fc [{delim-char
Define a delimiting and a padding character for fields. If the latter is missing, the padding character defaults to a space character. If there is no argument at all, the field mechanism is disabled (which is the default). Note that contrary to e.g. the tab repetition character, delimiting and padding characters are not associated to the current environment (see section 5.27 Environments).

Example:

 
.fc # ^
.ta T 3i
#foo^bar^smurf#
.br
#foo^^bar^smurf#

and here the result:

 
foo         bar          smurf
foo            bar       smurf

5.12 Character Translations

The control character (`.') and the no-break control character (`'') can be changed with the cc and c2 requests, respectively.

Request: .cc [{c
Set the control character to c. With no argument the default control character `.' is restored. The value of the control character is associated with the current environment (see section 5.27 Environments).

Request: .c2 [{c
Set the no-break control character to c. With no argument the default control character `'' is restored. The value of the no-break control character is associated with the current environment (see section 5.27 Environments).

Request: .eo \arg\
Disable the escape mechanism completely. After executing this request, the backslash character `\' no longer starts an escape sequence.

This request can be very helpful in writing macros since it is not necessary then to double the escape character. Here an example:

 
.\" This is a simplified version of the
.\" .BR request from the man macro package
.eo
.de BR
.  ds result \&
.  while (\n[.$] >= 2) \{\
.    as result \fB\$1\fR\$2
.    shift 2
.  \}
.  if \n[.$] .as result \fB\$1
\*[result]
.  ft R
..
.ec

Request: .ec [{c
Set the escape character to c. With no argument the default escape character `\' is restored. It can be also used to re-enable the escape mechanism after an eo request.

Note that changing the escape character globally will likely break macro packages since gtroff has no mechanism to `intern' macros, i.e., to convert a macro definition into an internal form which is independent of its representation (TeX has this mechanism). If a macro is called, it is executed literally.

Request: .ecs \arg\
Request: .ecr \arg\
The ecs request saves the current escape character in an internal register. Use this request in combination with the ec request to temporarily change the escape character.

The ecr request restores the escape character saved with ecs. Without a previous call to ecs, this request sets the escape character to \.

Escape: \, \delimI\\arg\\delimII\
Escape: \e\delimI\\arg\\delimII\
Escape: \E\delimI\\arg\\delimII\
Print the current escape character (which is the backslash character `\' by default).

\\ is a `delayed' backslash; more precisely, it is the default escape character followed by a backslash, which no longer has special meaning due to the leading escape character. It is not an escape sequence in the usual sense! In any unknown escape sequence \X the escape character is ignored and X is printed. But if X is equal to the current escape character, no warning is emitted.

As a consequence, only at top-level or in a diversion a backslash glyph is printed; in copy-in mode, it expands to a single backslash which then combines with the following character to an escape sequence.

The \E escape differs from \e by printing an escape character that is not interpreted in copy mode. Use this to define strings with escapes that work when used in copy mode (for example, as a macro argument). The following example defines strings to begin and end a superscript:

 
.ds { \v'-.3m'\s'\Es[.s]*60/100'
.ds } \s0\v'.3m'

Another example to demonstrate the differences between the various escape sequences, using a strange escape character, `-'.

 
.ec -
.de xxx
--A'123'
..
.xxx
    => -A'foo'

The result is surprising for most users, expecting `1' since `foo' is a valid identifier. What has happened? As mentioned above, the leading escape character makes the following character ordinary. Written with the default escape character the sequence `--' becomes `\-' -- this is the minus sign.

If the escape character followed by itself is a valid escape sequence, only \E yields the expected result:

 
.ec -
.de xxx
-EA'123'
..
.xxx
    => 1

Escape: \.\delimI\\arg\\delimII\
Similar to \\, the sequence \. isn't a real escape sequence. As before, a warning message is suppressed if the escape character is followed by a dot, and the dot itself is printed.

 
.de foo
.  nop foo
.
.  de bar
.    nop bar
\\..
.
..
.foo
.bar
    => foo bar

The first backslash is consumed while the macro is read, and the second is swallowed while exexuting macro foo.

A translation is a mapping of an input character to an output glyph. The mapping occurs at output time, i.e., the input character gets assigned the metric information of the mapped output character right before input tokens are converted to nodes (see section 5.33 gtroff Internals, for more on this process).

Request: .tr {a
Request: .trin {a
Translate character a to glyph b, character c to glyph d, etc. If there is an odd number of arguments, the last one is translated to an unstretchable space (`\ ').

The trin request is identical to tr, but when you unformat a diversion with asciify it ignores the translation. See section 5.26 Diversions, for details about the asciify request.

Some notes:

  • Special characters (\(xx, \[xxx], \C'xxx', \', \`, \-, \_), glyphs defined with the char request, and numbered glyphs (\N'xxx') can be translated also.

  • The \e escape can be translated also.

  • Characters can be mapped onto the \% and \~ escapes (but \% and \~ can't be mapped onto another glyph).

  • The following characters can't be translated: space (with one exception, see below), backspace, newline, leader (and \a), tab (and \t).

  • Translations are not considered for finding the soft hyphen character set with the shc request.

  • The pair `c\&' (this is an arbitrary character@w{ c followed by the zero width space character) maps this character to nothing.

     
    .tr a\&
    foo bar
        => foo br
    

    It is even possible to map the space character to nothing:

     
    .tr aa \&
    foo bar
        => foobar
    

    As shown in the example, the space character can't be the first character/glyph pair as an argument of tr. Additionally, it is not possible to map the space character to any other glyph; requests like `.tr aa x' undo `.tr aa \&' instead.

    If justification is active, lines are justified in spite of the `empty' space character (but there is no minimal distance, i.e. the space character, between words).

  • After an output glyph has been constructed (this happens at the moment immediately before the glyph is appended to an output glyph list, either by direct output, in a macro, diversion, or string), it is no longer affected by tr.

  • Translating character to glyphs where one of them or both are undefined is possible also; tr does not check whether the entities in its argument do exist.

    See section 5.33 gtroff Internals.

  • troff no longer has a hard-coded dependency on Latin-1; all charXXX entities have been removed from the font description files. This has a notable consequence which shows up in warnings like can't find character with input code XXX if the tr request isn't handled properly.

    Consider the following translation:

     
    .tr éÉ
    

    This maps input character é onto glyph É, which is identical to glyph char201. But this glyph intentionally doesn't exist! Instead, \[char201] is treated as an input character entity and is by default mapped onto \['E], and gtroff doesn't handle translations of translations.

    The right way to write the above translation is

     
    .tr é\['E]
    

    With other words, the first argument of tr should be an input character or entity, and the second one a glyph entity.

  • Without an argument, the tr request is ignored.

Request: .trnt {a
trnt is the same as the tr request except that the translations do not apply to text that is transparently throughput into a diversion with \!. See section 5.26 Diversions, for more information.

For example,

 
.tr ab
.di x
\!.tm a
.di
.x

prints `b' to the standard error stream; if trnt is used instead of tr it prints `a'.

5.13 Troff and Nroff Mode

Originally, nroff and troff were two separate programs, the former for TTY output, the latter for everything else. With GNU troff, both programs are merged into one executable, sending its output to a device driver (grotty for TTY devices, grops for POSTSCRIPT, etc.) which interprets the intermediate output of gtroff. For UNIX troff it makes sense to talk about Nroff mode and Troff mode since the differences are hardcoded. For GNU troff, this distinction is not appropriate because gtroff simply takes the information given in the font files for a particular device without handling requests specially if a TTY output device is used.

Usually, a macro package can be used with all output devices. Nevertheless, it is sometimes necessary to make a distinction between TTY and non-TTY devices: gtroff provides two built-in conditions `n' and `t' for the if, ie, and while requests to decide whether gtroff shall behave like nroff or like troff.

Request: .troff \arg\
Make the `t' built-in condition true (and the `n' built-in condition false) for if, ie, and while conditional requests. This is the default if gtroff (not groff) is started with the `-R' switch to avoid loading of the start-up files `troffrc' and `troffrc-end'. Without `-R', gtroff stays in troff mode if the output device is not a TTY (e.g. `ps').

Request: .nroff \arg\
Make the `n' built-in condition true (and the `t' built-in condition false) for if, ie, and while conditional requests. This is the default if gtroff uses a TTY output device; the code for switching to nroff mode is in the file `tty.tmac' which is loaded by the start-up file troffrc.

See section 5.21 Conditionals and Loops, for more details on built-in conditions.

5.14 Line Layout

The following drawing shows the dimensions which gtroff uses for placing a line of output onto the page. They are labeled with the request which manipulates each dimension.

 
                -->| in |<--
                   |<-----------ll------------>|
              +----+----+----------------------+----+
              |    :    :                      :    |
              +----+----+----------------------+----+
           -->| po |<--
              |<--------paper width---------------->|

These dimensions are:

po
Page offset -- this is the leftmost position of text on the final output, defining the left margin.

in
Indentation -- this is the distance from the left margin where text is printed.

ll
Line length -- this is the distance from the left margin to right margin.

A simple demonstration:

 
.ll 3i
This is text without indentation.
The line length has been set to 3\~inch.
.in +.5i
.ll -.5i
Now the left and right margins are both increased.
.in
.ll
Calling .in and .ll without parameters restore
the previous values.

Result:

 
This  is text without indenta-
tion.   The  line  length  has
been set to 3 inch.
     Now   the  left  and
     right  margins   are
     both increased.
Calling  .in  and  .ll without
parameters restore the  previ-
ous values.

Request: .po [{offset
Request: .po @t{+
Request: .po @t{-
Register: \n[.o]
Set horizontal page offset to offset (or increment or decrement the current value by offset). Note that this request does not cause a break, so changing the page offset in the middle of text being filled may not yield the expected result. The initial value is 1i. For TTY output devices, it is set to 0 in the startup file `troffrc'; the default scaling indicator is `m' (and not `v' as incorrectly documented in the original UNIX troff manual).

The current page offset can be found in the read-only number register `.o'.

If po is called without an argument, the page offset is reset to the previous value before the last call to po.

 
.po 3i
\n[.o]
    => 720
.po -1i
\n[.o]
    => 480
.po
\n[.o]
    => 720

Request: .in [{indent
Request: .in @t{+
Request: .in @t{-
Register: \n[.i]
Set indentation to indent (or increment or decrement the current value by indent). This request causes a break. Initially, there is no indentation.

If in is called without an argument, the indentation is reset to the previous value before the last call to in. The default scaling indicator is `m'.

The indentation is associated with the current environment (see section 5.27 Environments).

If a negative indentation value is specified (which is not allowed), gtroff emits a warning of type `range' and sets the indentation to zero.

The effect of in is delayed until a partially collected line (if it exists) is output. A temporary indent value is reset to zero also.

The current indentation (as set by in) can be found in the read-only number register `.i'.

Request: .ti offset
Request: .ti @t{+
Request: .ti @t{-
Register: \n[.in]
Temporarily indent the next output line by offset. If an increment or decrement value is specified, adjust the temporary indentation relative to the value set by the in request.

This request causes a break; its value is associated with the current environment (see section 5.27 Environments). The default scaling indicator is `m'. A call of ti without an argument is ignored.

If the total indentation value is negative (which is not allowed), gtroff emits a warning of type `range' and sets the temporary indentation to zero. `Total indentation' is either offset if specified as an absolute value, or the temporary plus normal indentation, if offset is given as a relative value.

The effect of ti is delayed until a partially collected line (if it exists) is output.

The read-only number register .in is the indentation that applies to the current output line.

The difference between .i and .in is that the latter takes into account whether a partially collected line still uses the old indentation value or a temporary indentation value is active.

Request: .ll [{length
Request: .ll @t{+
Request: .ll @t{-
Register: \n[.l]
Register: \n[.ll]
Set the line length to length (or increment or decrement the current value by length). Initially, the line length is set to 6.5i. The effect of ll is delayed until a partially collected line (if it exists) is output. The default scaling indicator is `m'.

If ll is called without an argument, the line length is reset to the previous value before the last call to ll. If a negative line length is specified (which is not allowed), gtroff emits a warning of type `range' and sets the line length to zero.

The line length is associated with the current environment (see section 5.27 Environments).

The current line length (as set by ll) can be found in the read-only number register `.l'. The read-only number register .ll is the line length that applies to the current output line.

Similar to .i and .in, the difference between .l and .ll is that the latter takes into account whether a partially collected line still uses the old line length value.

5.15 Line Control

It is important to understand how gtroff handles input and output lines.

Many escapes use positioning relative to the input line. For example, this

 
This is a \h'|1.2i'test.

This is a
\h'|1.2i'test.

produces

 
This is a   test.

This is a             test.

The main usage of this feature is to define macros which act exactly at the place where called.

 
.\" A simple macro to underline a word
.de underline
.  nop \\$1\l'|0\[ul]'
..

In the above example, `|0' specifies a negative distance from the current position (at the end of the just emitted argument \$1) back to the beginning of the input line. Thus, the `\l' escape draws a line from right to left.

gtroff makes a difference between input and output line continuation; the latter is also called interrupting a line.

Escape: @t{\RET\delimI\\arg\\delimII\
Escape: \c\delimI\\arg\\delimII\
Register: \n[.int]
Continue a line. \RET (this is a backslash at the end of a line immediately followed by a newline) works on the input level, suppressing the effects of the following newline in the input.

 
This is a \
.test
    => This is a .test

The `|' operator is also affected.

\c works on the output level. Anything after this escape on the same line is ignored, except \R which works as usual. Anything before \c on the same line will be appended to the current partial output line. The next non-command line after an interrupted line counts as a new input line.

The visual results depend on whether no-fill mode is active.

  • If no-fill mode is active (using the nf request), the next input text line after \c will be handled as a continuation of the same input text line.

     
    .nf
    This is a \c
    test.
        => This is a test.
    

  • If fill mode is active (using the fi request), a word interrupted with \c will be continued with the text on the next input text line, without an intervening space.

     
    This is a te\c
    st.
        => This is a test.
    

Note that an intervening control line which causes a break is stronger than \c, flushing out the current partial line in the usual way.

The .int register contains a positive value if the last output line was interrupted with \c; this is associated with the current environment (see section 5.27 Environments).

5.16 Page Layout

gtroff provides some very primitive operations for controlling page layout.

Request: .pl [{length
Request: .pl @t{+
Request: .pl @t{-
Register: \n[.p]
Set the page length to length (or increment or decrement the current value by length). This is the length of the physical output page. The default scaling indicator is `v'.

The current setting can be found in the read-only number register `.p'.

Note that this only specifies the size of the page, not the top and bottom margins. Those are not set by gtroff directly. See section 5.25 Traps, for further information on how to do this.

Negative pl values are possible also, but not very useful: No trap is sprung, and each line is output on a single page (thus suppressing all vertical spacing).

If no argument or an invalid argument is given, pl sets the page length to 11i.

gtroff provides several operations which help in setting up top and bottom titles (or headers and footers).

Request: .tl @t{'
Print a title line. It consists of three parts: a left justified portion, a centered portion, and a right justified portion. The argument separator `'' can be replaced with any character not occurring in the title line. The `%' character is replaced with the current page number. This character can be changed with the pc request (see below).

Without argument, tl is ignored.

Some notes:

  • A title line is not restricted to the top or bottom of a page.

  • tl prints the title line immediately, ignoring a partially filled line (which stays untouched).

  • It is not an error to omit closing delimiters. For example, `.tl /foo' is equivalent to `.tl /foo///': It prints a title line with the left justified word `foo'; the centered and right justfied parts are empty.

  • tl accepts the same parameter delimiting characters as the \A escape; see 5.6.3 Escapes.

Request: .lt [{length
Request: .lt @t{+
Request: .lt @t{-
Register: \n[.lt]
The title line is printed using its own line length, which is specified (or incremented or decremented) with the lt request. Initially, the title line length is set to 6.5i. If a negative line length is specified (which is not allowed), gtroff emits a warning of type `range' and sets the title line length to zero. The default scaling indicator is `m'. If lt is called without an argument, the title length is reset to the previous value before the last call to lt.

The current setting of this is available in the .lt read-only number register; it is associated with the current environment (see section 5.27 Environments).

Request: .pn page
Request: .pn @t{+
Request: .pn @t{-
Register: \n[.pn]
Change (increase or decrease) the page number of the next page. The only argument is the page number; the request is ignored without a parameter.

The read-only number register .pn contains the number of the next page: either the value set by a pn request, or the number of the current page plus 1.

Register: \n[%]
A read-write register holding the current page number.

Request: .pc [{char
Change the page number character (used by the tl request) to a different character. With no argument, this mechanism is disabled. Note that this doesn't affect the number register %.

See section 5.25 Traps.

5.17 Page Control

Request: .bp [{page
Request: .bp @t{+
Request: .bp @t{-
Stop processing the current page and move to the next page. This request causes a break. It can also take an argument to set (increase, decrease) the page number of the next page. The only difference between bp and pn is that pn does not cause a break or actually eject a page.

 
.de newpage                         \" define macro
'bp                                 \" begin page
'sp .5i                             \" vertical space
.tl 'left top'center top'right top' \" title
'sp .3i                             \" vertical space
..                                  \" end macro

bp has no effect if not called within the top-level diversion (see section 5.26 Diversions).

Request: .ne [{space
It is often necessary to force a certain amount of space before a new page occurs. This is most useful to make sure that there is not a single orphan line left at the bottom of a page. The ne request ensures that there is a certain distance, specified by the first argument, before the next page is triggered (see 5.25 Traps, for further information). The default scaling indicator for ne is `v'; the default value of space is 1v if no argument is given.

For example, to make sure that no fewer than 2 lines get orphaned, do the following before each paragraph:

 
.ne 2
text text text

ne will then automatically cause a page break if there is space for one line only.

Request: .sv [{space
Request: .os \arg\
sv is similar to the ne request; it reserves the specified amount of vertical space. If the desired amount of space exists before the next trap (or the bottom page boundary if no trap is set), the space is output immediately (ignoring a partially filled line which stays untouched). If there is not enough space, it is stored for later output via the os request. The default value is 1v if no argument is given; the default scaling indicator is `v'.

Both sv and os ignore no-space mode. While the sv request allows negative values for space, os will ignore them.

Register: \n[nl]
This register contains the current vertical position. If the vertical position is zero and the top of page transition hasn't happened yet, nl is set to negative value. gtroff itself does this at the very beginning of a document before anything has been printed, but the main usage is to plant a header trap on a page if this page has already started.

Consider the following:

 
.de xxx
.  sp
.  tl ''Header''
.  sp
..
.
First page.
.bp
.wh 0 xxx
.nr nl (-1)
Second page.

Result:

 
First page.

...

                             Header

Second page.

...

Without resetting nl to a negative value, the just planted trap would be active beginning with the next page, not the current one.

See section 5.26 Diversions, for a comparison with the .h and .d registers.

5.18 Fonts

gtroff can switch fonts at any point in the text.

The basic set of fonts is `R', `I', `B', and `BI'. These are Times Roman, Italic, Bold, and Bold Italic. For non-TTY devices, there is also at least one symbol font which contains various special symbols (Greek, mathematics).

5.18.1 Changing Fonts  
5.18.2 Font Families  
5.18.3 Font Positions  
5.18.4 Using Symbols  
5.18.5 Special Fonts  
5.18.6 Artificial Fonts  
5.18.7 Ligatures and Kerning  

5.18.1 Changing Fonts

Request: .ft [{font
Escape: \ff\delimII\
Escape: @t{\f(\arg\\delimII\
Escape: @t{\f[\arg\\delimII\
The ft request and the \f escape change the current font to font (one-character name f, two-character name fn).

If font is a style name (as set with the sty request or with the styles command in the `DESC' file), use it within the current font family (as set with the fam request, \F escape, or with the family command in the `DESC' file).

With no argument or using `P' as an argument, .ft switches to the previous font. Use \f[] to do this with the escape. The old syntax forms \fP or \f[P] are also supported.

Fonts are generally specified as upper-case strings, which are usually 1 to 4 characters representing an abbreviation or acronym of the font name. This is no limitation, just a convention.

The example below produces two identical lines.

 
eggs, bacon,
.ft B
spam
.ft
and sausage.

eggs, bacon, \fBspam\fP and sausage.

Note that \f doesn't produce an input token in gtroff. As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the font on the fly:

 
.mc \f[I]x\f[]

See section 5.18.3 Font Positions, for an alternative syntax.

Request: .ftr f [{g
Translate font f to font g. Whenever a font named@w{ f is referred to in a \f escape sequence, or in the ft, ul, bd, cs, tkf, special, fspecial, fp, or sty requests, font g is used. If g is missing or equal to f the translation is undone.

5.18.2 Font Families

Due to the variety of fonts available, gtroff has added the concept of font families and font styles. The fonts are specified as the concatenation of the font family and style. Specifying a font without the family part causes gtroff to use that style of the current family.

Currently, fonts for the devices `-Tps', `-Tdvi', and `-Tlbp' are set up to this mechanism. By default, gtroff uses the Times family with the four styles `R', `I', `B', and `BI'.

This way, it is possible to use the basic four fonts and to select a different font family on the command line (see section 2.1 Options).

Request: .fam [{family
Register: \n[.fam]
Escape: \Ff\delimII\
Escape: @t{\F(\arg\\delimII\
Escape: @t{\F[\arg\\delimII\
Register: \n[.fn]
Switch font family to family (one-character name f, two-character name fm). If no argument is given, switch back to the previous font family. Use \F[] to do this with the escape. Note that \FP doesn't work; it selects font family `P' instead.

The value at start-up is `T'. The current font family is available in the read-only number register `.fam' (this is a string-valued register); it is associated with the current environment.

 
spam,
.fam H    \" helvetica family
spam,     \" used font is family H + style R = HR
.ft B     \" family H + style B = font HB
spam,
.fam T    \" times family
spam,     \" used font is family T + style B = TB
.ft AR    \" font AR (not a style)
baked beans,
.ft R     \" family T + style R = font TR
and spam.

Note that \F doesn't produce an input token in gtroff. As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the font family on the fly:

 
.mc \F[P]x\F[]

The `.fn' register contains the current real font name of the current font. This is a string-valued register. If the current font is a style, the value of \n[.fn] is the proper concatenation of family and style name.

Request: .sty n style
Associate style with font position n. A font position can be associated either with a font or with a style. The current font is the index of a font position and so is also either a font or a style. If it is a style, the font that is actually used is the font which name is the concatenation of the name of the current family and the name of the current style. For example, if the current font is 1 and font position 1 is associated with style `R' and the current font family is `T', then font `TR' will be used. If the current font is not a style, then the current family is ignored. If the requests cs, bd, tkf, uf, or fspecial are applied to a style, they will instead be applied to the member of the current family corresponding to that style.

n must be a non-negative integer value.

The default family can be set with the `-f' option (see section 2.1 Options). The styles command in the `DESC' file controls which font positions (if any) are initially associated with styles rather than fonts. For example, the default setting for POSTSCRIPT fonts

 
styles R I B BI

is equivalent to

 
.sty 1 R
.sty 2 I
.sty 3 B
.sty 4 BI

fam and \F always check whether the current font position is valid; this can give surprising results if the current font position is associated with a style.

In the following example, we want to access the POSTSCRIPT font FooBar from the font family Foo:

 
.sty \n[.fp] Bar
.fam Foo
    => warning: can't find font `FooR'

The default font position at start-up is 1; for the POSTSCRIPT device, this is associated with style `R', so gtroff tries to open FooR.

A solution to this problem is to use a dummy font like the following:

 
.fp 0 dummy TR    \" set up dummy font at position 0
.sty \n[.fp] Bar  \" register style `Bar'
.ft 0             \" switch to font at position 0
.fam Foo          \" activate family `Foo'
.ft Bar           \" switch to font `FooBar'

See section 5.18.3 Font Positions.

5.18.3 Font Positions

For the sake of old phototypesetters and compatibility with old versions of troff, gtroff has the concept of font positions, on which various fonts are mounted.

Request: .fp pos font [{external-name
Register: \n[.f]
Register: \n[.fp]
Mount font font at position pos (which must be a non-negative integer). This numeric position can then be referred to with font changing commands. When gtroff starts it is using font position 1 (which must exist; position 0 is unused usually at start-up).

The current font in use, as a font position, is available in the read-only number register `.f'. This can be useful to remember the current font for later recall. It is associated with the current environment (see section 5.27 Environments).

 
.nr save-font \n[.f]
.ft B
... text text text ...
.ft \n[save-font]

The number of the next free font position is available in the read-only number register `.fp'. This is useful when mounting a new font, like so:

 
.fp \n[.fp] NEATOFONT

Fonts not listed in the `DESC' file are automatically mounted on the next available font position when they are referenced. If a font is to be mounted explicitly with the fp request on an unused font position, it should be mounted on the first unused font position, which can be found in the .fp register. Although gtroff does not enforce this strictly, it is not allowed to mount a font at a position whose number is much greater (approx. 1000 positions) than that of any currently used position.

The fp request has an optional third argument. This argument gives the external name of the font, which is used for finding the font description file. The second argument gives the internal name of the font which is used to refer to the font in gtroff after it has been mounted. If there is no third argument then the internal name is used as the external name. This feature makes it possible to use fonts with long names in compatibility mode.

Both the ft request and the \f escape have alternative syntax forms to access font positions.

Request: .ft nnn
Escape: \fn\delimII\
Escape: @t{\f(\arg\\delimII\
Escape: @t{\f[\arg\\delimII\
Change the current font position to nnn (one-digit position@w{ n, two-digit position nn), which must be a non-negative integer.

If nnn is associated with a style (as set with the sty request or with the styles command in the `DESC' file), use it within the current font family (as set with the fam request, the \F escape, or with the family command in the `DESC' file).

 
this is font 1
.ft 2
this is font 2
.ft                   \" switch back to font 1
.ft 3
this is font 3
.ft
this is font 1 again

See section 5.18.1 Changing Fonts, for the standard syntax form.

5.18.4 Using Symbols

A glyph is a graphical representation of a character. While a character is an abstract entity containing semantic information, a glyph is something which can be actually seen on screen or paper. It is possible that a character has multiple glyph representation forms (for example, the character `A' can be either written in a roman or an italic font, yielding two different glyphs); sometimes more than one character maps to a single glyph (this is a ligature -- the most common is `fi').

A symbol is simply a named glyph. Within gtroff, all glyph names of a particular font are defined in its font file. If the user requests a glyph not available in this font, gtroff looks up an ordered list of special fonts. By default, the POSTSCRIPT output device supports the two special fonts `SS' (slanted symbols) and `S' (symbols) (the former is looked up before the latter). Other output devices use different names for special fonts. Fonts mounted with the fonts keyword in the `DESC' file are globally available. To install additional special fonts locally (i.e. for a particular font), use the fspecial request.

In summary, gtroff tries the following to find a given symbol:

  • If the symbol has been defined with the char request, use it. This hides a symbol with the same name in the current font.

  • Check the current font.

  • If the symbol has been defined with the fchar request, use it.

  • Check all fonts given with the fspecial request, in the order of appearance in fspecial calls.

  • Check all fonts given with the special request, in the order of appearance in special calls (inclusively the special fonts defined in the `DESC' file, which come first).

  • As a last resort, consult all fonts loaded up to now (in the order they have been called the first time) for special fonts and check them.

See section 8.2 Font Files, and 5.18.5 Special Fonts, for more details.

Escape: @t{, ({\delimI\\arg\\delimII\
Escape: @t{, [{\delimI\\arg\\delimII\
Insert a symbol name (two-character name nm). There is no special syntax for one-character names -- the natural form `\n' would collide with escapes.@footnotegroff_114.html{Note that a one-character symbol is not the same as an input character, i.e., the character a is not the same as \[a]. By default, groff defines only a single one-character symbol, \[-]; it is usually accessed as \-. On the other hand, gtroff has the special feature that \[charXXX] is the same as the input character with character code XXX. For example, \[char97] is identical to the letter a if ASCII encoding is active.

If name is undefined, a warning of type `char' is generated, and the escape is ignored. See section 5.34 Debugging, for information about warnings.

The list of available symbols is device dependent; see the groff_char(7) man page for a complete list for the given output device. For example, say

 
man -Tdvi groff_char > groff_char.dvi

for a list using the default DVI fonts (not all versions of the man program support the `-T' option). If you want to use an additional macro package to change the used fonts, groff must be called directly:

 
groff -Tdvi -mec -man groff_char.7 > groff_char.dvi

Escape: \C'xxx'
Typeset the glyph named xxx.@footnotegroff_114.html{\C is actually a misnomer since it accesses an output glyph. Normally it is more convenient to use \[xxx], but \C has the advantage that it is compatible with newer versions of AT&T troff and is available in compatibility mode.

Escape: \N'n'
Typeset the glyph with code n in the current font (n is not the input character code). The number n can be any non-negative decimal integer. Most devices only have glyphs with codes between 0 and 255; the Unicode output device uses codes in the range 0--65535. If the current font does not contain a glyph with that code, special fonts are not searched. The \N escape sequence can be conveniently used in conjunction with the char request:

 
.char \[phone] \f[ZD]\N'37'

The code of each glyph is given in the fourth column in the font description file after the charset command. It is possible to include unnamed glyphs in the font description file by using a name of `---'; the \N escape sequence is the only way to use these.

Some escape sequences directly map onto special glyphs.

Escape: \'\delimI\\arg\\delimII\
This is a backslash followed by the apostrophe character, ASCII character 0x27 (EBCDIC character 0x7D). The same as \[aa], the acute accent.

Escape: \`\delimI\\arg\\delimII\
This is a backslash followed by ASCII character 0x60 (EBCDIC character 0x79 usually). The same as \[ga], the grave accent.

Escape: \-\delimI\\arg\\delimII\
This is the same as \[-], the minus sign in the current font.

Request: .cflags n c1 c2 @dots{
Input characters and symbols have certain properties associated with it.@footnotegroff_114.html{Note that the output glyphs themselves don't have such properties. For gtroff, a glyph is a numbered box with a given width, depth, and height, nothing else. All manipulations with the cflags request work on the input level. These properties can be modified with the cflags request. The first argument is the sum of the desired flags and the remaining arguments are the characters or symbols to have those properties. It is possible to omit the spaces between the characters or symbols.

1
The character ends sentences (initially characters `.?!' have this property).

2
Lines can be broken before the character (initially no characters have this property).

4
Lines can be broken after the character (initially the character `-' and the symbols `\(hy' and `\(em' have this property).

8
The character overlaps horizontally (initially the symbols `\(ul\(rn\(ru' have this property).

16
The character overlaps vertically (initially symbol `\(br' has this property).

32
An end-of-sentence character followed by any number of characters with this property is treated as the end of a sentence if followed by a newline or two spaces; in other words the character is transparent for the purposes of end-of-sentence recognition -- this is the same as having a zero space factor in TeX (initially characters `"')]*' and the symbols `\(dg\(rq' have this property).

Request: .char g [{string
Request: .fchar g [{string
Define a new glyph g to be string (which can be empty).@footnotegroff_114.html{char is a misnomer since an output glyph is defined. Every time glyph g needs to be printed, string is processed in a temporary environment and the result is wrapped up into a single object. Compatibility mode is turned off and the escape character is set to `\' while string is being processed. Any emboldening, constant spacing or track kerning is applied to this object rather than to individual characters in string.

A glyph defined by this request can be used just like a normal glyph provided by the output device. In particular, other characters can be translated to it with the tr or trin requests; it can be made the leader character by the lc request; repeated patterns can be drawn with the glyph using the \l and \L escape sequences; words containing the glyph can be hyphenated correctly if the hcode request is used to give the glyph's symbol a hyphenation code.

There is a special anti-recursion feature: Use of g within the glyph's definition is handled like normal characters and symbols not defined with char.

Note that the tr and trin requests take precedence if char accesses the same symbol.

 
.tr XY
X
    => Y
.char X Z
X
    => Y
.tr XX
X
    => Z

The fchar request defines a fallback glyph: gtroff only checks for glyphs defined with fchar if it cannot find the glyph in the current font. gtroff carries out this test before checking special fonts.

Request: .rchar c1 c2 @dots{
Remove the definitions of glyphs c1, c2,@w{ .... This undoes the effect of a char or fchar request.

It is possible to omit the whitespace between arguments.

See section 7.1 Special Characters.

5.18.5 Special Fonts

Special fonts are those that gtroff searches when it cannot find the requested glyph in the current font. The Symbol font is usually a special font.

gtroff provides the following two requests to add more special fonts. See section 5.18.4 Using Symbols, for a detailed description of the glyph searching mechanism in gtroff.

Usually, only non-TTY devices have special fonts.

Request: .special s1 s2 @dots{
Request: .fspecial f s1 s2 @dots{
Use the special request to define special fonts. They are appended to the list of global special fonts in the given order. The first entries in this list are the fonts defined with the fonts command in the `DESC' file which are marked as special in the corresponding font description files.

Use the fspecial request to designate special fonts only when font f font is active. They are appended to the list of special fonts for f in the given order. Initially, this list is empty.

5.18.6 Artificial Fonts

There are a number of requests and escapes for artificially creating fonts. These are largely vestiges of the days when output devices did not have a wide variety of fonts, and when nroff and troff were separate programs. Most of them are no longer necessary in GNU troff. Nevertheless, they are supported.

Escape: \H'height'
Escape: \H'+\delimII\
Escape: \H'-\delimII\
Change (increment, decrement) the height of the current font, but not the width. If height is zero, restore the original height. Default scaling indicator is `z'.

Currently, only the `-Tps' device supports this feature.

Note that \H doesn't produce an input token in gtroff. As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the font on the fly:

 
.mc \H'+5z'x\H'0'

In compatibility mode, gtroff behaves differently: If an increment or decrement is used, it is always taken relative to the current point size and not relative to the previously selected font height. Thus,

 
.cp 1
\H'+5'test \H'+5'test

prints the word `test' twice with the same font height (five points larger than the current font size).

Escape: \S'slant'
Slant the current font by slant degrees. Positive values slant to the right.

Currently, only the `-Tps' device supports this feature.

Note that \S doesn't produce an input token in gtroff. As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the font on the fly:

 
.mc \S'20'x\S'0'

This request is incorrectly documented in the original UNIX troff manual; the slant is always set to an absolute value.

Request: .ul [{lines
The ul request normally underlines subsequent lines if a TTY output device is used. Otherwise, the lines are printed in italics (only the term `underlined' is used in the following). The single argument is the number of input lines to be underlined; with no argument, the next line is underlined. If lines is zero or negative, stop the effects of ul (if it was active). Requests and empty lines do not count for computing the number of underlined input lines, even if they produce some output like tl. Lines inserted by macros (e.g. invoked by a trap) do count.

At the beginning of ul, the current font is stored and the underline font is activated. Within the span of a ul request, it is possible to change fonts, but after the last line affected by ul the saved font is restored.

This number of lines still to be underlined is associated with the current environment (see section 5.27 Environments). The underline font can be changed with the uf request.

The ul request does not underline spaces.

Request: .cu [{lines
The cu request is similar to ul but underlines spaces as well (if a TTY output device is used).

Request: .uf font
Set the underline font (globally) used by ul and cu. By default, this is the font at position 2. font can be either a non-negative font position or the name of a font.

Request: .bd font [{offset
Request: .bd font1 font2 [{offset
Register: \n[.b]
Artificially create a bold font by printing each glyph twice, slightly offset.

Two syntax forms are available.

  • Imitate a bold font unconditionally. The first argument specifies the font to embolden, and the second is the number of basic units, minus one, by which the two glyphs are offset. If the second argument is missing, emboldening is turned off.

    font can be either a non-negative font position or the name of a font.

    offset is available in the .b read-only register if a special font is active; in the bd request, its default unit is `u'.

  • Imitate a bold form conditionally. Embolden font1 by offset only if font font2 is the current font. This command can be issued repeatedly to set up different emboldening values for different current fonts. If the second argument is missing, emboldening is turned off for this particular current font.

    This affects special fonts only (either set up with the special command in font files or with the fspecial request).

Request: .cs font [{width
Switch to and from constant glyph space mode. If activated, the width of every glyph is width/36 ems. The em size is given absolutely by em-size; if this argument is missing, the em value is taken from the current font size (as set with the ps request) when the font is effectively in use. Without second and third argument, constant glyph space mode is deactivated.

Default scaling indicator for em-size is `z'; width is an integer.

5.18.7 Ligatures and Kerning

Ligatures are groups of characters that are run together, i.e, producing a single glyph. For example, the letters `f' and `i' can form a ligature `fi' as in the word `file'. This produces a cleaner look (albeit subtle) to the printed output. Usually, ligatures are not available in fonts for TTY output devices.

Most POSTSCRIPT fonts support the fi and fl ligatures. The C/A/T typesetter that was the target of AT&T troff also supported `ff', `ffi', and `ffl' ligatures. Advanced typesetters or `expert' fonts may include ligatures for `ft' and `ct', although GNU troff does not support these (yet).

Request: .lg [{flag
Register: \n[.lg]
Switch the ligature mechanism on or off; if the parameter is non-zero or missing, ligatures are enabled, otherwise disabled. Default is on. The current ligature mode can be found in the read-only number register .lg (set to 1 or 2 if ligatures are enabled, 0 otherwise).

Setting the ligature mode to 2 enables the two-character ligatures (fi, fl, and ff) and disables the three-character ligatures (ffi and ffl).

Pairwise kerning is another subtle typesetting mechanism that modifies the distance between a glyph pair to improve readability. In most cases (but not always) the distance is decreased. For example, compare the combination of the letters `V' and `A'. With kerning, `VA' is printed. Without kerning it appears as `VA'. Typewriter-like fonts and fonts for terminals where all glyphs have the same width don't use kerning.

Request: .kern [{flag
Register: \n[.kern]
Switch kerning on or off. If the parameter is non-zero or missing, enable pairwise kerning, otherwise disable it. The read-only number register .kern is set to 1 if pairwise kerning is enabled, 0 otherwise.

If the font description file contains pairwise kerning information, glyphs from that font are kerned. Kerning between two glyphs can be inhibited by placing \& between them: `V\&A'.

See section 8.2.2 Font File Format.

Track kerning expands or reduces the space between glyphs. This can be handy, for example, if you need to squeeze a long word onto a single line or spread some text to fill a narrow column. It must be used with great care since it is usually considered bad typography if the reader notices the effect.

Request: .tkf f s1 n1 s2 n2
Enable track kerning for font f. If the current font is f the width of every glyph is increased by an amount between n1 and n2 (n1, n2 can be negative); if the current point size is less than or equal to s1 the width is increased by n1; if it is greater than or equal to s2 the width is increased by n2; if the point size is greater than or equal to s1 and less than or equal to s2 the increase in width is a linear function of the point size.

The default scaling indicator is `z' for s1 and s2, `p' for n1 and n2.

Note that the track kerning amount is added even to the rightmost glyph in a line; for large values it is thus recommended to increase the line length by the same amount to compensate it.

Sometimes, when typesetting letters of different fonts, more or less space at such boundaries are needed. There are two escapes to help with this.

Escape: \/\delimI\\arg\\delimII\
Increase the width of the preceding glyph so that the spacing between that glyph and the following glyph is correct if the following glyph is a roman glyph. For example, if an italic f is immediately followed by a roman right parenthesis, then in many fonts the top right portion of the f overlaps the top left of the right parenthesis. Use this escape sequence whenever an italic glyph is immediately followed by a roman glyph without any intervening space. This small amount of space is also called italic correction.

Escape: \,\delimI\\arg\\delimII\
Modify the spacing of the following glyph so that the spacing between that glyph and the preceding glyph is correct if the preceding glyph is a roman glyph. Use this escape sequence whenever a roman glyph is immediately followed by an italic glyph without any intervening space. In analogy to above, this space could be called left italic correction, but this term isn't used widely.

Escape: \&\delimI\\arg\\delimII\
Insert a zero-width character, which is invisible. Its intended use is to stop interaction of a character with its surrounding.

  • It prevents the insertion of extra space after an end-of-sentence character.

     
    Test.
    Test.
        => Test.  Test.
    Test.\&
    Test.
        => Test. Test.
    

  • It prevents interpretation of a control character at the beginning of an input line.

     
    .Test
        => warning: `Test' not defined
    \&.Test
        => .Test
    

  • It prevents kerning between two glyphs.

     
    VA
        => VA
    V\&A
        => VA
    

  • It is needed to map an arbitrary character to nothing in the tr request (see section 5.12 Character Translations).

Escape: \)\delimI\\arg\\delimII\
This escape is similar to \& except that it behaves like a character declared with the cflags request to be transparent for the purposes of an end-of-sentence character.

Its main usage is in macro definitions to protect against arguments starting with a control character.

 
.de xxx
\)\\$1
..
.de yyy
\&\\$1
..
This is a test.\c
.xxx '
This is a test.
    =>This is a test.'  This is a test.
This is a test.\c
.yyy '
This is a test.
    =>This is a test.' This is a test.

5.19 Sizes

gtroff uses two dimensions with each line of text, type size and vertical spacing. The type size is approximately the height of the tallest glyph.@footnotegroff_118.html{This is usually the parenthesis. Note that in most cases the real dimensions of the glyphs in a font are not related to its type size! For example, the standard POSTSCRIPT font families `Times Roman', `Helvetica', and `Courier' can't be used together at 10pt; to get acceptable output, the size of `Helvetica' has to be reduced by one point, and the size of `Courier' must be increased by one point. Vertical spacing is the amount of space gtroff allows for a line of text; normally, this is about 20% larger than the current type size. Ratios smaller than this can result in hard-to-read text; larger than this, it spreads the text out more vertically (useful for term papers). By default, gtroff uses 10 point type on 12 point spacing.

The difference between type size and vertical spacing is known, by typesetters, as leading (this is pronounced `ledding').

5.19.1 Changing Type Sizes  
5.19.2 Fractional Type Sizes  

5.19.1 Changing Type Sizes

Request: .ps [{size
Request: .ps +
Request: .ps -
Escape: \ssize\delimII\
Register: \n[.s]
Use the ps request or the \s escape to change (increase, decrease) the type size (in points). Specify size as either an absolute point size, or as a relative change from the current size. The size 0, or no argument, goes back to the previous size.

Default scaling indicator of size is `z'. If size is zero or negative, it is set to 1u.

The read-only number register .s returns the point size in points as a decimal fraction. This is a string. To get the point size in scaled points, use the .ps register instead.

.s is associated with the current environment (see section 5.27 Environments).

 
snap, snap,
.ps +2
grin, grin,
.ps +2
wink, wink, \s+2nudge, nudge,\s+8 say no more!
.ps 10

The \s escape may be called in a variety of ways. Much like other escapes there must be a way to determine where the argument ends and the text begins. Any of the following forms are valid:

\sn
Set the point size to n points. n must be either 0 or in the range 4 to 39.

\s+n
\s-n
Increase or decrease the point size by n points. n must be exactly one digit.

\s(nn
Set the point size to nn points. nn must be exactly two digits.

\s+(nn
\s-(nn
\s(+nn
\s(-nn
Increase or decrease the point size by nn points. nn must be exactly two digits.

Note that \s doesn't produce an input token in gtroff. As a consequence, it can be used in requests like mc (which expects a single character as an argument) to change the font on the fly:

 
.mc \s[20]x\s[0]

See section 5.19.2 Fractional Type Sizes, for yet another syntactical form of using the \s escape.

Request: .sizes s1 s2 @dots{
Some devices may only have certain permissible sizes, in which case gtroff rounds to the nearest permissible size. The `DESC' file specifies which sizes are permissible for the device.

Use the sizes request to change the permissible sizes for the current output device. Arguments are in scaled points; the sizescale line in the `DESC' file for the output device provides the scaling factor. For example, if the scaling factor is 1000, then the value 12000 is 12 points.

Each argument can be a single point size (such as `12000'), or a range of sizes (such as `4000-72000'). You can optionally end the list with a zero.

Request: .vs [{space
Request: .vs @t{+
Request: .vs @t{-
Register: \n[.v]
Change (increase, decrease) the vertical spacing by space. The default scaling indicator is `p'.

If vs is called without an argument, the vertical spacing is reset to the previous value before the last call to vs.

gtroff creates a warning of type `range' if space is zero or negative; the vertical spacing is then set to the vertical resolution (as given in the .V register).

The read-only number register .v contains the current vertical spacing; it is associated with the current environment (see section 5.27 Environments).

The effective vertical line spacing consists of four components.

  • The vertical line spacing as set with the vs request.

  • The post-vertical line spacing as set with the pvs request. This is vertical space which will be added after a line has been output.

  • The extra pre-vertical line space as set with the \x request, using a negative value. This is vertical space which will be added once before the current line has been output.

  • The extra post-vertical line space as set with the \x request, using a positive value. This is vertical space which will be added once after the current line has been output.

It is usually better to use vs or pvs instead of ls to produce double-spaced documents: vs and pvs have a finer granularity for the inserted vertical space compared to ls; furthermore, certain preprocessors assume single-spacing.

See section 5.10 Manipulating Spacing, for more details on the \x escape and the ls request.

Request: .pvs [{space
Request: .pvs @t{+
Request: .pvs @t{-
Register: \n[.pvs]
Change (increase, decrease) the post-vertical spacing by space. The default scaling indicator is `p'.

If pvs is called without an argument, the post-vertical spacing is reset to the previous value before the last call to pvs.

gtroff creates a warning of type `range' if space is zero or negative; the vertical spacing is then set to zero.

The read-only number register .pvs contains the current post-vertical spacing; it is associated with the current environment (see section 5.27 Environments).

5.19.2 Fractional Type Sizes

A scaled point is equal to 1/sizescale points, where sizescale is specified in the `DESC' file (1 by default). There is a new scale indicator `z' which has the effect of multiplying by sizescale. Requests and escape sequences in gtroff interpret arguments that represent a point size as being in units of scaled points, but they evaluate each such argument using a default scale indicator of `z'. Arguments treated in this way are the argument to the ps request, the third argument to the cs request, the second and fourth arguments to the tkf request, the argument to the \H escape sequence, and those variants of the \s escape sequence that take a numeric expression as their argument (see below).

For example, suppose sizescale is 1000; then a scaled point is equivalent to a millipoint; the request `.ps 10.25' is equivalent to `.ps 10.25z' and thus sets the point size to 10250 scaled points, which is equal to 10.25 points.

gtroff disallows the use of the `z' scale indicator in instances where it would make no sense, such as a numeric expression whose default scale indicator was neither `u' nor `z'. Similarly it would make no sense to use a scaling indicator other than `z' or `u' in a numeric expression whose default scale indicator was `z', and so gtroff disallows this as well.

There is also new scale indicator `s' which multiplies by the number of units in a scaled point. So, for example, `\n[.ps]s' is equal to `1m'. Be sure not to confuse the `s' and `z' scale indicators.

Register: \n[.ps]
A read-only number register returning the point size in scaled points.

.ps is associated with the current environment (see section 5.27 Environments).

Register: \n[.psr]
Register: \n[.sr]
The last-requested point size in scaled points is contained in the .psr read-only number register. The last requested point size in points as a decimal fraction can be found in .sr. This is a string-valued read-only number register.

Note that the requested point sizes are device-independent, whereas the values returned by the .ps and .s registers are not. For example, if a point size of 11pt is requested, and a sizes request (or a sizescale line in a `DESC' file) specifies 10.95pt instead, this value is actually used.

Both registers are associated with the current environment (see section 5.27 Environments).

The \s escape has the following syntax for working with fractional type sizes:

\s[n]
\s'n'
Set the point size to n scaled points; n is a numeric expression with a default scale indicator of `z'.

\s[+n]
\s[-n]
\s+[n]
\s-[n]
\s'+n'
\s'-n'
\s+'n'
\s-'n'
Increase or or decrease the point size by n scaled points; n is a numeric expression with a default scale indicator of `z'.

See section 8.2 Font Files.

5.20 Strings

gtroff has string variables, which are entirely for user convenience (i.e. there are no built-in strings exept .T, but even this is a read-write string variable).

Request: .ds name [{string
Request: .ds1 name [{string
Escape: \*n\delimII\
Escape: @t{\*(\arg\\delimII\
Escape: @t{\*[\arg\\delimII\
Define and access a string variable name (one-character name@w{ n, two-character name nm). If name already exists, ds overwrites the previous definition. Only the syntax form using brackets can take arguments which are handled identically to macro arguments; the single exception is that a closing bracket as an argument must be enclosed in double quotes. See section 5.6.1.1 Request Arguments, and 5.22.2 Parameters.

Example:

 
.ds foo a \\$1 test
.
This is \*[foo nice].
    => This is a nice test.

The \* escape interpolates (expands in-place) a previously-defined string variable. To be more precise, the stored string is pushed onto the input stack which is then parsed by gtroff. Similar to number registers, it is possible to nest strings, i.e. string variables can be called within string variables.

If the string named by the \* escape does not exist, it is defined as empty, and a warning of type `mac' is emitted (see 5.34 Debugging, for more details).

Caution: Unlike other requests, the second argument to the ds request takes up the entire line including trailing spaces. This means that comments on a line with such a request can introduce unwanted space into a string.

 
.ds UX \s-1UNIX\s0\u\s-3tm\s0\d \" UNIX trademark

Instead the comment should be put on another line or have the comment escape adjacent with the end of the string.

 
.ds UX \s-1UNIX\s0\u\s-3tm\s0\d\"  UNIX trademark

To produce leading space the string can be started with a double quote. No trailing quote is needed; in fact, any trailing quote is included in your string.

 
.ds sign "           Yours in a white wine sauce,

Strings are not limited to a single line of text. A string can span several lines by escaping the newlines with a backslash. The resulting string is stored without the newlines.

 
.ds foo lots and lots \
of text are on these \
next several lines

It is not possible to have real newlines in a string. To put a single double quote character into a string, use two consecutive double quote characters.

The ds1 request turns off compatibility mode while interpreting a string. To be more precise, a @dfn{compatibility save input token is inserted at the beginning of the string, and a compatibility restore input token at the end.

 
.nr xxx 12345
.ds aa The value of xxx is \\n[xxx].
.ds1 bb The value of xxx ix \\n[xxx].
.
.cp 1
.
\*(aa
    => warning: number register `[' not defined
    => The value of xxx is 0xxx].
\*(bb
    => The value of xxx ix 12345.

Strings, macros, and diversions (and boxes) share the same name space. Internally, even the same mechanism is used to store them. This has some interesting consequences. For example, it is possible to call a macro with string syntax and vice versa.

 
.de xxx
a funny test.
..
This is \*[xxx]
    => This is a funny test.

.ds yyy a funny test
This is
.yyy
    => This is a funny test.

Diversions and boxes can be also called with string syntax.

Another consequence is that you can copy one-line diversions or boxes to a string.

 
.di xxx
a \fItest\fR
.br
.di
.ds yyy This is \*[xxx]\c
\*[yyy].
    => This is a test.

As the previous example shows, it is possible to store formatted output in strings. The \c escape prevents the insertion of an additional blank line in the output.

Copying diversions longer than a single output line produces unexpected results.

 
.di xxx
a funny
.br
test
.br
.di
.ds yyy This is \*[xxx]\c
\*[yyy].
    => test This is a funny.

Usually, it is not predictable whether a diversion contains one or more output lines, so this mechanism should be avoided. With UNIX troff, this was the only solution to strip off a final newline from a diversion. Another disadvantage is that the spaces in the copied string are already formatted, making them unstretchable. This can cause ugly results.

A clean solution to this problem is available in GNU troff, using the requests chop to remove the final newline of a diversion, and unformat to make the horizontal spaces stretchable again.

 
.box xxx
a funny
.br
test
.br
.box
.chop xxx
.unformat xxx
This is \*[xxx].
    => This is a funny test.

See section 5.33 gtroff Internals, for more information.

Request: .as name [{string
Request: .as1 name [{string
The as request is similar to ds but appends string to the string stored as name instead of redefining it. If name doesn't exist yet, it is created.

 
.as sign " with shallots, onions and garlic,

The as1 request is similar to as, but compatibility mode is switched off while the appended string is interpreted. To be more precise, a compatibility save input token is inserted at the beginning of the appended string, and a compatibility restore input token at the end.

Rudimentary string manipulation routines are given with the next two requests.

Request: .substring str n1 [{n2
Replace the string named str with the substring defined by the indices n1 and n2. The first character in the string has index 0. If n2 is omitted, it is taken to be equal to the string's length. If the index value n1 or n2 is negative, it is counted from the end of the string, going backwards: The last character has index -1, the character before the last character has index -2, etc.

 
.ds xxx abcdefgh
.substring xxx 1 -4
\*[xxx]
    => bcde

Request: .length reg str
Compute the number of characters of str and return it in the number register reg. If reg doesn't exist, it is created. str is read in copy mode.

 
.ds xxx abcd\h'3i'efgh
.length yyy \n[xxx]
\n[yyy]
    => 14

Request: .rn xx yy
Rename the request, macro, diversion, or string xx to yy.

Request: .rm xx
Remove the request, macro, diversion, or string xx. gtroff treats subsequent invocations as if the object had never been defined.

Request: .als new old
Create an alias named new for the request, string, macro, or diversion object named old. The new name and the old name are exactly equivalent (it is similar to a hard rather than a soft link). If old is undefined, gtroff generates a warning of type `mac' and ignores the request.

Request: .chop xx
Remove (chop) the last character from the macro, string, or diversion named xx. This is useful for removing the newline from the end of diversions that are to be interpolated as strings. This command can be used repeatedly; see 5.33 gtroff Internals, for details on nodes inserted additionally by gtroff.

See section 5.5 Identifiers, and 5.6.3.1 Comments.

5.21 Conditionals and Loops

5.21.1 Operators in Conditionals  
5.21.2 if-else  
5.21.3 while  

5.21.1 Operators in Conditionals

In if and while requests, there are several more operators available:

e
o
True if the current page is even or odd numbered (respectively).

n
True if the document is being processed in nroff mode (i.e., the .nroff command has been issued).

t
True if the document is being processed in troff mode (i.e., the .troff command has been issued).

v
Always false. This condition is for compatibility with other troff versions only.

'xxx'yyy'
True if the string xxx is equal to the string yyy. Other characters can be used in place of the single quotes; the same set of delimiters as for the \D escape is used (see section 5.6.3 Escapes). gtroff formats the strings before being compared:

 
.ie "|"\fR|\fP" \
true
.el \
false
    => true

The resulting motions, glyph sizes, and fonts have to match,@footnotegroff_123.html{The created output nodes must be identical. See section 5.33 gtroff Internals. and not the individual motion, size, and font requests. In the previous example, `|' and `\fR|\fP' both result in a roman `|' glyph with the same point size and at the same location on the page, so the strings are equal. If `.ft I' had been added before the `.ie', the result would be "false" because (the first) `|' produces an italic `|' rather than a roman one.

r xxx
True if there is a number register named xxx.

d xxx
True if there is a string, macro, diversion, or request named xxx.

m xxx
True if there is a color named xxx.

c g
True if there is a glyph g available@footnotegroff_123.html{The name of this conditional operator is a misnomer since it tests names of output glyphs.

(7)

Margin character is a misnomer since it is an output glyph. The first argument is the glyph to be printed. The second argument is the distance away from the right margin. If missing, the previously set value is used; default is 10pt). For text lines that are too long (that is, longer than the text length plus dist), the margin character is directly appended to the lines.

With no arguments the margin character is turned off. If this occurs before a break, no margin character is printed.

For empty lines and lines produced by the tl request no margin character is emitted.

The margin character is associated with the current environment (see section 5.27 Environments).

This is quite useful for indicating text that has changed, and, in fact, there are programs available for doing this (they are called nrchbar and changebar and can be found in any `comp.sources.unix' archive.

 
.ll 3i
.mc |
This paragraph is highlighted with a margin
character.
.sp
Note that vertical space isn't marked.
.br
\&
.br
But we can fake it with `\&'.

Result:

 
This  paragraph is highlighted |
with a margin character.       |

Note that vertical space isn't |
marked.                        |
                               |
But we can fake it with `\&'.  |

Request: .psbb filename
Register: \n[llx]
Register: \n[lly]
Register: \n[urx]
Register: \n[ury]
Retrieve the bounding box of the PostScript image found in filename. The file must conform to Adobe's Document Structuring Conventions (DSC); the command searches for a %%BoundingBox comment and extracts the bounding box values into the number registers llx, lly, urx, and ury. If an error occurs (for example, psbb cannot find the %%BoundingBox comment), it sets the four number registers to zero.

5.33 gtroff Internals

gtroff processes input in three steps. One or more input characters are converted to an input token.@footnotegroff_144.html{Except the escapes \f, \F, \H, \m, \M, \R, \s, and \S which are processed immediately if not in copy-in mode. Then, one or more input tokens are converted to an output node. Finally, output nodes are converted to the intermediate output language understood by all output devices.

Actually, before step one happens, gtroff converts certain escape sequences into reserved input characters (not accessible by the user); such reserved characters are used for other internal processing also -- this is the very reason why not all characters are valid input. See section 5.5 Identifiers, for more on this topic.

For example, the input string `fi\[:u]' is converted into a character token `f', a character token `i', and a special token `:u' (representing u umlaut). Later on, the character tokens `f' and `i' are merged to a single output node representing the ligature glyph `fi' (provided the current font has a glyph for this ligature); the same happens with `:u'. All output glyph nodes are `processed' which means that they are invariably associated with a given font, font size, advance width, etc. During the formatting process, gtroff itself adds various nodes to control the data flow.

Macros, diversions, and strings collect elements in two chained lists: a list of input tokens which have been passed unprocessed, and a list of output nodes. Consider the following the diversion.

 
.di xxx
a
\!b
c
.br
.di

It contains these elements.

node list token list element number
line start node -- 1
glyph node a -- 2
word space node -- 3
-- b 4
-- \n 5
glyph node c -- 6
vertical size node -- 7
vertical size node -- 8
-- \n 9

Elements 1, 7, and 8 are inserted by gtroff; the latter two (which are always present) specify the vertical extent of the last line, possibly modified by \x. The br request finishes the current partial line, inserting a newline input token which is subsequently converted to a space when the diversion is reread. Note that the word space node has a fixed width which isn't stretchable anymore. To convert horizontal space nodes back to input tokens, use the unformat request.

Macros only contain elements in the token list (and the node list is empty); diversions and strings can contain elements in both lists.

Note that the chop request simply reduces the number of elements in a macro, string, or diversion by one. Exceptions are compatibility save and compatibility ignore input tokens which are ignored. The substring request also ignores those input tokens.

Some requests like tr or cflags work on glyph identifiers only; this means that the associated glyph can be changed without destroying this association. This can be very helpful for substituting glyphs. In the following example, we assume that glyph `foo' isn't available by default, so we provide a substitution using the fchar request and map it to input character `x'.

 
.fchar \[foo] foo
.tr x \[foo]

Now let us assume that we install an additional special font `bar' which has glyph `foo'.

 
.special bar
.rchar \[foo]

Since glyphs defined with fchar are searched before glyphs in special fonts, we must call rchar to remove the definition of the fallback glyph. Anyway, the translation is still active; `x' now maps to the real glyph `foo'.

5.34 Debugging

gtroff is not easy to debug, but there are some useful features and strategies for debugging.

Request: .lf line filename
Change the line number and the file name gtroff shall use for error and warning messages. line is the input line number of the next line.

Without argument, the request is ignored.

This is a debugging aid for documents which are split into many files, then put together with soelim and other preprocessors. Usually, it isn't invoked manually.

Request: .tm string
Request: .tm1 string
Request: .tmc string
Send string to the standard error output; this is very useful for printing debugging messages among other things.

string is read in copy mode.

The tm request ignores leading spaces of string; tm1 handles its argument similar to the ds request: a leading double quote in string is stripped to allow initial blanks.

The tmc request is similar to tm1 but does not append a newline (as is done in tm and tm1).

Request: .ab [{string
Similar to the tm request, except that it causes gtroff to stop processing. With no argument it prints `User Abort.' to standard error.

Request: .ex \arg\
The ex request also causes gtroff to stop processing; see also 5.30 I/O.

When doing something involved it is useful to leave the debugging statements in the code and have them turned on by a command line flag.

 
.if \n(DB .tm debugging output

To activate these statements say

 
groff -rDB=1 file

If it is known in advance that there will be many errors and no useful output, gtroff can be forced to suppress formatted output with the `-z' flag.

Request: .pm \arg\
Print the entire symbol table on stderr. Names of all defined macros, strings, and diversions are print together with their size in bytes. Since gtroff sometimes adds nodes by itself, the returned size can be larger than expected.

This request differs from UNIX troff: gtroff reports the sizes of diversions, ignores an additional argument to print only the total of the sizes, and the size isn't returned in blocks of 128 characters.

Request: .pnr \arg\
Print the names and contents of all currently defined number registers on stderr.

Request: .ptr \arg\
Print the names and positions of all traps (not including input line traps and diversion traps) on stderr. Empty slots in the page trap list are printed as well, because they can affect the priority of subsequently planted traps.

Request: .fl \arg\
Instruct gtroff to flush its output immediately. The intent is for interactive use, but this behaviour is currently not implemented in gtroff. Contrary to UNIX troff, TTY output is sent to a device driver also (grotty), making it non-trivial to communicate interactively.

This request causes a line break.

Request: .backtrace \arg\
Print a backtrace of the input stack to the standard error stream.

Consider the following in file `test':

 
.de xxx
.  backtrace
..
.de yyy
.  xxx
..
.
.yyy

On execution, gtroff prints the following:

 
test:2: backtrace: macro `xxx'
test:5: backtrace: macro `yyy'
test:8: backtrace: file `test'

The option `-b' of gtroff internally calls a variant of this request on each error and warning.

Register: \n[slimit]
Use the slimit number register to set the maximum number of objects on the input stack. If slimit is less than or equal to 0, there is no limit set. With no limit, a buggy recursive macro can exhaust virtual memory.

The default value is 1000; this is a compile-time constant.

Request: .warnscale si
Set the scaling indicator used in warnings to si. Valid values for si are `u', `i', `c', `p', and `P'. At startup, it is set to `i'.

Request: .spreadwarn [{limit
Make gtroff emit a warning if the additional space inserted for each space between words in an output line is larger or equal to limit. A negative value is changed to zero; no argument toggles the warning on and off without changing limit. The default scaling indicator is `m'. At startup, spreadwarn is deactivated, and limit is set to 3m.

For example,

 
.spreadwarn 0.2m

will cause a warning if gtroff must add 0.2m or more for each interword space in a line.

This request is active only if text is justified to both margins (using `.ad b').

gtroff has command line options for printing out more warnings (`-w') and for printing backtraces (`-b') when a warning or an error occurs. The most verbose level of warnings is `-ww'.

Request: .warn [{flags
Register: \n[.warn]
Control the level of warnings checked for. The flags are the sum of the numbers associated with each warning that is to be enabled; all other warnings are disabled. The number associated with each warning is listed below. For example, .warn 0 disables all warnings, and .warn 1 disables all warnings except that about missing glyphs. If no argument is given, all warnings are enabled.

The read-only number register .warn contains the current warning level.

5.34.1 Warnings  

5.34.1 Warnings

The warnings that can be given to gtroff are divided into the following categories. The name associated with each warning is used by the `-w' and `-W' options; the number is used by the warn request and by the .warn register.

`char'
`1'
Non-existent glyphs.@footnotegroff_146.html{char is a misnomer since it reports missing glyphs -- there aren't missing input characters, only invalid ones. This is enabled by default.

`number'
`2'
Invalid numeric expressions. This is enabled by default. See section 5.4 Expressions.

`break'
`4'
In fill mode, lines which could not be broken so that their length was less than the line length. This is enabled by default.

`delim'
`8'
Missing or mismatched closing delimiters.

`el'
`16'
Use of the el request with no matching ie request. See section 5.21.2 if-else.

`scale'
`32'
Meaningless scaling indicators.

`range'
`64'
Out of range arguments.

`syntax'
`128'
Dubious syntax in numeric expressions.

`di'
`256'
Use of di or da without an argument when there is no current diversion.

`mac'
`512'
Use of undefined strings, macros and diversions. When an undefined string, macro, or diversion is used, that string is automatically defined as empty. So, in most cases, at most one warning is given for each name.

`reg'
`1024'
Use of undefined number registers. When an undefined number register is used, that register is automatically defined to have a value of 0. So, in most cases, at most one warning is given for use of a particular name.

`tab'
`2048'
Use of a tab character where a number was expected.

`right-brace'
`4096'
Use of \} where a number was expected.

`missing'
`8192'
Requests that are missing non-optional arguments.

`input'
`16384'
Invalid input characters.

`escape'
`32768'
Unrecognized escape sequences. When an unrecognized escape sequence \X is encountered, the escape character is ignored, and X is printed.

`space'
`65536'
Missing space between a request or macro and its argument. This warning is given when an undefined name longer than two characters is encountered, and the first two characters of the name make a defined name. The request or macro is not invoked. When this warning is given, no macro is automatically defined. This is enabled by default. This warning never occurs in compatibility mode.

`font'
`131072'
Non-existent fonts. This is enabled by default.

`ig'
`262144'
Invalid escapes in text ignored with the ig request. These are conditions that are errors when they do not occur in ignored text.

`color'
`524288'
Color related warnings.

`all'
All warnings except `di', `mac' and `reg'. It is intended that this covers all warnings that are useful with traditional macro packages.

`w'
All warnings.

5.35 Implementation Differences

GNU troff has a number of features which cause incompatibilities with documents written with old versions of troff.

Long names cause some incompatibilities. UNIX troff interprets

 
.dsabcd

as defining a string `ab' with contents `cd'. Normally, GNU troff interprets this as a call of a macro named dsabcd. Also UNIX troff interprets \*[ or \n[ as references to a string or number register called `['. In GNU troff, however, this is normally interpreted as the start of a long name. In compatibility mode GNU troff interprets long names in the traditional way (which means that they are not recognized as names).

Request: .cp [{n
Request: .do cmd
Register: \n[.C]
If n is missing or non-zero, turn on compatibility mode; otherwise, turn it off.

The read-only number register .C is 1 if compatibility mode is on, 0 otherwise.

Compatibility mode can be also turned on with the `-C' command line option.

The do request turns off compatibility mode while executing its arguments as a gtroff command.

 
.do fam T

executes the fam request when compatibility mode is enabled.

gtroff restores the previous compatibility setting before interpreting any files sourced by the cmd.

Two other features are controlled by `-C'. If not in compatibility mode, GNU troff preserves the input level in delimited arguments:

 
.ds xx '
\w'abc\*(xxdef'

In compatibility mode, the string `72def'' is returned; without `-C' the resulting string is `168' (assuming a TTY output device).

Finally, the escapes \f, \H, \m, \M, \R, \s, and \S are transparent for recognizing the beginning of a line only in compatibility mode (this is a rather obscure feature). For example, the code

 
.de xx
Hallo!
..
\fB.xx\fP

prints `Hallo!' in bold face if in compatibility mode, and `.xx' in bold face otherwise.

GNU troff does not allow the use of the escape sequences \|, \^, \&, \{, \}, \SP, \', \`, \-, \_, \!, \%, and \c in names of strings, macros, diversions, number registers, fonts or environments; UNIX troff does. The \A escape sequence (see section 5.5 Identifiers) may be helpful in avoiding use of these escape sequences in names.

Fractional point sizes cause one noteworthy incompatibility. In UNIX troff the ps request ignores scale indicators and thus

 
.ps 10u

sets the point size to 10 points, whereas in GNU troff it sets the point size to 10 scaled points. See section 5.19.2 Fractional Type Sizes, for more information.

In GNU troff there is a fundamental difference between (unformatted) input characters and (formatted) output glyphs. Everything that affects how a glyph is output is stored with the glyph node; once a glyph node has been constructed it is unaffected by any subsequent requests that are executed, including bd, cs, tkf, tr, or fp requests. Normally glyphs are constructed from input characters at the moment immediately before the glyph is added to the current output line. Macros, diversions and strings are all, in fact, the same type of object; they contain lists of input characters and glyph nodes in any combination. A glyph node does not behave like an input character for the purposes of macro processing; it does not inherit any of the special properties that the input character from which it was constructed might have had. For example,

 
.di x
\\\\
.br
.di
.x

prints `\\' in GNU troff; each pair of input backslashes is turned into one output backslash and the resulting output backslashes are not interpreted as escape characters when they are reread. UNIX troff would interpret them as escape characters when they were reread and would end up printing one `\'. The correct way to obtain a printable backslash is to use the \e escape sequence: This always prints a single instance of the current escape character, regardless of whether or not it is used in a diversion; it also works in both GNU troff and UNIX troff.@footnotegroff_147.html{To be completely independent of the current escape character, use \(rs which represents a reverse solidus (backslash) glyph. To store, for some reason, an escape sequence in a diversion that will be interpreted when the diversion is reread, either use the traditional \! transparent output facility, or, if this is unsuitable, the new \? escape sequence.

See section 5.26 Diversions, and 5.33 gtroff Internals, for more information.

6. Preprocessors

This chapter describes all preprocessors that come with groff or which are freely available.

6.1 geqn  
6.2 gtbl  
6.3 gpic  
6.4 ggrn  
6.5 grap  
6.6 grefer  
6.7 gsoelim  

6.1 geqn

6.1.1 Invoking geqn  

6.1.1 Invoking geqn

6.2 gtbl

6.2.1 Invoking gtbl  

6.2.1 Invoking gtbl

6.3 gpic

6.3.1 Invoking gpic  

6.3.1 Invoking gpic

6.4 ggrn

6.4.1 Invoking ggrn  

6.4.1 Invoking ggrn

6.5 grap

A free implementation of grap, written by Ted Faber, is available as an extra package from the following address:

 
http://www.lunabase.org/~faber/Vault/software/grap/

6.6 grefer

6.6.1 Invoking grefer  

6.6.1 Invoking grefer

6.7 gsoelim

6.7.1 Invoking gsoelim  

6.7.1 Invoking gsoelim

7. Output Devices

7.1 Special Characters  
7.2 grotty  
7.3 grops  
7.4 grodvi  
7.5 grolj4  
7.6 grolbp  
7.7 grohtml  
7.8 gxditview  

7.1 Special Characters

See section 8.2 Font Files.

7.2 grotty

7.2.1 Invoking grotty  

7.2.1 Invoking grotty

7.3 grops

7.3.1 Invoking grops  
7.3.2 Embedding POSTSCRIPT  

7.3.1 Invoking grops

7.3.2 Embedding POSTSCRIPT

7.4 grodvi

7.4.1 Invoking grodvi  

7.4.1 Invoking grodvi

7.5 grolj4

7.5.1 Invoking grolj4  

7.5.1 Invoking grolj4

7.6 grolbp

7.6.1 Invoking grolbp  

7.6.1 Invoking grolbp

7.7 grohtml

7.7.1 Invoking grohtml  
7.7.2 grohtml specific registers and strings  

7.7.1 Invoking grohtml

7.7.2 grohtml specific registers and strings

Register: \n[ps4html]
String: \*[www-image-template]
The registers ps4html and www-image-template are defined by the pre-grohtml preprocessor. pre-grohtml reads in the troff input, marks up the inline equations and passes the result firstly to

 
troff -Tps -rps4html=1 -dwww-image-template=template

and secondly to

 
troff -Thtml

The PostScript device is used to create all the image files, and the register ps4html enables the macro sets to ignore floating keeps, footers, and headings.

The register www-image-template is set to the user specified template name or the default name.

7.8 gxditview

7.8.1 Invoking gxditview  

7.8.1 Invoking gxditview

8. File formats

All files read and written by gtroff are text files. The following two sections describe their format.

8.1 gtroff Output  
8.2 Font Files  

8.1 gtroff Output

This section describes the intermediate output format of GNU troff. This output is produced by a run of gtroff before it is fed into a device postprocessor program.

As groff is a wrapper program around gtroff that automatically calls a postprocessor, this output does not show up normally. This is why it is called intermediate. groff provides the option `-Z' to inhibit postprocessing, such that the produced intermediate output is sent to standard output just like calling gtroff manually.

Here, the term troff output describes what is output by gtroff, while intermediate output refers to the language that is accepted by the parser that prepares this output for the postprocessors. This parser is smarter on whitespace and implements obsolete elements for compatibility, otherwise both formats are the same.@footnotegroff_181.html{The parser and postprocessor for intermediate output can be found in the file
`groff-source-dir/src/libs/libdriver/input.cc'.

The main purpose of the intermediate output concept is to facilitate the development of postprocessors by providing a common programming interface for all devices. It has a language of its own that is completely different from the gtroff language. While the gtroff language is a high-level programming language for text processing, the intermediate output language is a kind of low-level assembler language by specifying all positions on the page for writing and drawing.

The intermediate output produced by gtroff is fairly readable, while output from AT&T troff is rather hard to understand because of strange habits that are still supported, but not used any longer by gtroff.

8.1.1 Language Concepts  
8.1.2 Command Reference  
8.1.3 Intermediate Output Examples  
8.1.4 Output Language Compatibility  

8.1.1 Language Concepts

During the run of gtroff, the input data is cracked down to the information on what has to be printed at what position on the intended device. So the language of the intermediate output format can be quite small. Its only elements are commands with and without arguments. In this section, the term command always refers to the intermediate output language, and never to the gtroff language used for document formatting. There are commands for positioning and text writing, for drawing, and for device controlling.

8.1.1.1 Separation  
8.1.1.2 Argument Units  
8.1.1.3 Document Parts  

8.1.1.1 Separation

AT&T troff output has strange requirements on whitespace. The gtroff output parser, however, is smart about whitespace by making it maximally optional. The whitespace characters, i.e., the tab, space, and newline characters, always have a syntactical meaning. They are never printable because spacing within the output is always done by positioning commands.

Any sequence of space or tab characters is treated as a single syntactical space. It separates commands and arguments, but is only required when there would occur a clashing between the command code and the arguments without the space. Most often, this happens when variable-length command names, arguments, argument lists, or command clusters meet. Commands and arguments with a known, fixed length need not be separated by syntactical space.

A line break is a syntactical element, too. Every command argument can be followed by whitespace, a comment, or a newline character. Thus a syntactical line break is defined to consist of optional syntactical space that is optionally followed by a comment, and a newline character.

The normal commands, those for positioning and text, consist of a single letter taking a fixed number of arguments. For historical reasons, the parser allows to stack such commands on the same line, but fortunately, in gtroff's intermediate output, every command with at least one argument is followed by a line break, thus providing excellent readability.

The other commands -- those for drawing and device controlling -- have a more complicated structure; some recognize long command names, and some take a variable number of arguments. So all `D' and `x' commands were designed to request a syntactical line break after their last argument. Only one command, `x X', has an argument that can stretch over several lines; all other commands must have all of their arguments on the same line as the command, i.e., the arguments may not be splitted by a line break.

Empty lines (these are lines containing only space and/or a comment), can occur everywhere. They are just ignored.

8.1.1.2 Argument Units

Some commands take integer arguments that are assumed to represent values in a measurement unit, but the letter for the corresponding scale indicator is not written with the output command arguments. Most commands assume the scale indicator `u', the basic unit of the device, some use `z', the scaled point unit of the device, while others, such as the color commands, expect plain integers.

Note that single characters can have the eighth bit set, as can the names of fonts and special characters. The names of characters and fonts can be of arbitrary length. A character that is to be printed will always be in the current font.

A string argument is always terminated by the next whitespace character (space, tab, or newline); an embedded `#' character is regarded as part of the argument, not as the beginning of a comment command. An integer argument is already terminated by the next non-digit character, which then is regarded as the first character of the next argument or command.

8.1.1.3 Document Parts

A correct intermediate output document consists of two parts, the prologue and the body.

The task of the prologue is to set the general device parameters using three exactly specified commands. gtroff's prologue is guaranteed to consist of the following three lines (in that order):

 
x T device
x res n h v
x init

with the arguments set as outlined in 8.1.2.4 Device Control Commands. Note that the parser for the intermediate output format is able to swallow additional whitespace and comments as well even in the prologue.

The body is the main section for processing the document data. Syntactically, it is a sequence of any commands different from the ones used in the prologue. Processing is terminated as soon as the first `x stop' command is encountered; the last line of any gtroff intermediate output always contains such a command.

Semantically, the body is page oriented. A new page is started by a `p' command. Positioning, writing, and drawing commands are always done within the current page, so they cannot occur before the first `p' command. Absolute positioning (by the `H' and `V' commands) is done relative to the current page; all other positioning is done relative to the current location within this page.

8.1.2 Command Reference

This section describes all intermediate output commands, both from AT&T troff as well as the gtroff extensions.

8.1.2.1 Comment Command  
8.1.2.2 Simple Commands  
8.1.2.3 Graphics Commands  
8.1.2.4 Device Control Commands  
8.1.2.5 Obsolete Command  

8.1.2.1 Comment Command

#anything<end of line>
A comment. Ignore any characters from the `#' character up to the next newline character.

This command is the only possibility for commenting in the intermediate output. Each comment can be preceded by arbitrary syntactical space; every command can be terminated by a comment.

8.1.2.2 Simple Commands

The commands in this subsection have a command code consisting of a single character, taking a fixed number of arguments. Most of them are commands for positioning and text writing. These commands are smart about whitespace. Optionally, syntactical space can be inserted before, after, and between the command letter and its arguments. All of these commands are stackable, i.e., they can be preceded by other simple commands or followed by arbitrary other commands on the same line. A separating syntactical space is only necessary when two integer arguments would clash or if the preceding argument ends with a string argument.

C xxx<whitespace>
Print a special character named xxx. The trailing syntactical space or line break is necessary to allow glyph names of arbitrary length. The glyph is printed at the current print position; the glyph's size is read from the font file. The print position is not changed.

c g
Print glyph g at the current print position;@footnotegroff_188.html{`c' is actually a misnomer since it outputs a glyph. the glyph's size is read from the font file. The print position is not changed.

f n
Set font to font number n (a non-negative integer).

H n
Move right to the absolute vertical position n (a non-negative integer in basic units `u' relative to left edge of current page.

h n
Move n (a non-negative integer) basic units `u' horizontally to the right. The original UNIX troff manual allows negative values for n also, but gtroff doesn't use this.

m color-scheme [component ...]
Set the color for text (glyphs), line drawing, and the outline of graphic objects using different color schemes; the analoguous command for the filling color of graphic objects is `DF'. The color components are specified as integer arguments between 0 and 65536. The number of color components and their meaning vary for the different color schemes. These commands are generated by gtroff's escape sequence \m. No position changing. These commands are a gtroff extension.

mc cyan magenta yellow
Set color using the CMY color scheme, having the 3 color components cyan, magenta, and yellow.

md
Set color to the default color value (black in most cases). No component arguments.

mg gray
Set color to the shade of gray given by the argument, an integer between 0 (black) and 65536 (white).

mk cyan magenta yellow black
Set color using the CMYK color scheme, having the 4 color components cyan, magenta, yellow, and black.

mr red green blue
Set color using the RGB color scheme, having the 3 color components red, green, and blue.

N n
Print glyph with index n (a non-negative integer) of the current font. This command is a gtroff extension.

n b a
Inform the device about a line break, but no positioning is done by this command. In AT&T troff, the integer arguments b and a informed about the space before and after the current line to make the intermediate output more human readable without performing any action. In groff, they are just ignored, but they must be provided for compatibility reasons.

p n
Begin a new page in the outprint. The page number is set to n. This page is completely independent of pages formerly processed even if those have the same page number. The vertical position on the outprint is automatically set to 0. All positioning, writing, and drawing is always done relative to a page, so a `p' command must be issued before any of these commands.

s n
Set point size to n scaled points (this is unit `z'). AT&T troff used the unit points (`p') instead. See section 8.1.4 Output Language Compatibility.

t xxx<whitespace>
t xxx dummy-arg<whitespace>
Print a word, i.e., a sequence of characters xxx representing output glyphs which names are single characters, terminated by a space character or a line break; an optional second integer argument is ignored (this allows the formatter to generate an even number of arguments). The first glyph should be printed at the current position, the current horizontal position should then be increased by the width of the first glyph, and so on for each glyph. The widths of the glyphs are read from the font file, scaled for the current point size, and rounded to a multiple of the horizontal resolution. Special characters cannot be printed using this command (use the `C' command for special characters). This command is a gtroff extension; it is only used for devices whose `DESC' file contains the tcommand keyword (see section 8.2.1 `DESC' File Format).

u n xxx<whitespace>
Print word with track kerning. This is the same as the `t' command except that after printing each glyph, the current horizontal position is increased by the sum of the width of that glyph and n (an integer in basic units `u'). This command is a gtroff extension; it is only used for devices whose `DESC' file contains the tcommand keyword (see section 8.2.1 `DESC' File Format).

V n
Move down to the absolute vertical position n (a non-negative integer in basic units `u') relative to upper edge of current page.

v n
Move n basic units `u' down (n is a non-negative integer). The original UNIX troff manual allows negative values for n also, but gtroff doesn't use this.

w
Informs about a paddable white space to increase readability. The spacing itself must be performed explicitly by a move command.

8.1.2.3 Graphics Commands

Each graphics or drawing command in the intermediate output starts with the letter `D', followed by one or two characters that specify a subcommand; this is followed by a fixed or variable number of integer arguments that are separated by a single space character. A `D' command may not be followed by another command on the same line (apart from a comment), so each `D' command is terminated by a syntactical line break.

gtroff output follows the classical spacing rules (no space between command and subcommand, all arguments are preceded by a single space character), but the parser allows optional space between the command letters and makes the space before the first argument optional. As usual, each space can be any sequence of tab and space characters.

Some graphics commands can take a variable number of arguments. In this case, they are integers representing a size measured in basic units `u'. The arguments called h1, h2, ..., hn stand for horizontal distances where positive means right, negative left. The arguments called v1, v2, ..., vn stand for vertical distances where positive means down, negative up. All these distances are offsets relative to the current location.

Unless indicated otherwise, each graphics command directly corresponds to a similar gtroff \D escape sequence. See section 5.24 Drawing Requests.

Unknown `D' commands are assumed to be device-specific. Its arguments are parsed as strings; the whole information is then sent to the postprocessor.

In the following command reference, the syntax element <line break> means a syntactical line break as defined above.

D~ h1 v1 h2 v2 ... hn vn<line break>
Draw B-spline from current position to offset (h1,v1), then to offset (h2,v2), if given, etc. up to (hn,vn). This command takes a variable number of argument pairs; the current position is moved to the terminal point of the drawn curve.

Da h1 v1 h2 v2<line break>
Draw arc from current position to (h1,v1)+(h2,v2) with center at (h1,v1); then move the current position to the final point of the arc.

DC d<line break>
DC d dummy-arg<line break>
Draw a solid circle using the current fill color with diameter d (integer in basic units `u') with leftmost point at the current position; then move the current position to the rightmost point of the circle. An optional second integer argument is ignored (this allows the formatter to generate an even number of arguments). This command is a gtroff extension.

Dc d<line break>
Draw circle line with diameter d (integer in basic units `u') with leftmost point at the current position; then move the current position to the rightmost point of the circle.

DE h v<line break>
Draw a solid ellipse in the current fill color with a horizontal diameter of h and a vertical diameter of v (both integers in basic units `u') with the leftmost point at the current position; then move to the rightmost point of the ellipse. This command is a gtroff extension.

De h v<line break>
Draw an outlined ellipse with a horizontal diameter of h and a vertical diameter of v (both integers in basic units `u') with the leftmost point at current position; then move to the rightmost point of the ellipse.

DF color-scheme [component ...]<line break>
Set fill color for solid drawing objects using different color schemes; the analoguous command for setting the color of text, line graphics, and the outline of graphic objects is `m'. The color components are specified as integer arguments between 0 and 65536. The number of color components and their meaning vary for the different color schemes. These commands are generated by gtroff's escape sequences \D'F ...' and \M (with no other corresponding graphics commands). No position changing. This command is a gtroff extension.

DFc cyan magenta yellow<line break>
Set fill color for solid drawing objects using the CMY color scheme, having the 3 color components cyan, magenta, and yellow.

DFd<line break>
Set fill color for solid drawing objects to the default fill color value (black in most cases). No component arguments.

DFg gray<line break>
Set fill color for solid drawing objects to the shade of gray given by the argument, an integer between 0 (black) and 65536 (white).

DFk cyan magenta yellow black<line break>
Set fill color for solid drawing objects using the CMYK color scheme, having the 4 color components cyan, magenta, yellow, and black.

DFr red green blue<line break>
Set fill color for solid drawing objects using the RGB color scheme, having the 3 color components red, green, and blue.

Df n<line break>
The argument n must be an integer in the range -32767 to 32767.

0 <= n <= 1000
Set the color for filling solid drawing objects to a shade of gray, where 0 corresponds to solid white, 1000 (the default) to solid black, and values in between to intermediate shades of gray; this is obsoleted by command `DFg'.

n < 0 or n < 1000
Set the filling color to the color that is currently being used for the text and the outline, see command `m'. For example, the command sequence

 
mg 0 0 65536
Df -1

sets all colors to blue.

No position changing. This command is a gtroff extension.

Dl h v<line break>
Draw line from current position to offset (h,v) (integers in basic units `u'); then set current position to the end of the drawn line.

Dp h1 v1 h2 v2 ... hn vn<line break>
Draw a polygon line from current position to offset (h1,v1), from there to offset (h2,v2), etc. up to offset (hn,vn), and from there back to the starting position. For historical reasons, the position is changed by adding the sum of all arguments with odd index to the actual horizontal position and the even ones to the vertical position. Although this doesn't make sense it is kept for compatibility. This command is a gtroff extension.

Dp h1 v1 h2 v2 ... hn vn<line break>
Draw a solid polygon in the current fill color rather than an outlined polygon, using the same arguments and positioning as the corresponding `Dp' command. This command is a gtroff extension.

Dt n<line break>
Set the current line thickness to n (an integer in basic units `u') if n>0; if n=0 select the smallest available line thickness; if n<0 set the line thickness proportional to the point size (this is the default before the first `Dt' command was specified). For historical reasons, the horizontal position is changed by adding the argument to the actual horizontal position, while the vertical position is not changed. Although this doesn't make sense it is kept for compatibility. This command is a gtroff extension.

8.1.2.4 Device Control Commands

Each device control command starts with the letter `x', followed by a space character (optional or arbitrary space or tab in gtroff) and a subcommand letter or word; each argument (if any) must be preceded by a syntactical space. All `x' commands are terminated by a syntactical line break; no device control command can be followed by another command on the same line (except a comment).

The subcommand is basically a single letter, but to increase readability, it can be written as a word, i.e., an arbitrary sequence of characters terminated by the next tab, space, or newline character. All characters of the subcommand word but the first are simply ignored. For example, gtroff outputs the initialization command `x i' as `x init' and the resolution command `x r' as `x res'.

In the following, the syntax element <line break> means a syntactical line break (see section 8.1.1.1 Separation).

xF name<line break>
The `F' stands for Filename.

Use name as the intended name for the current file in error reports. This is useful for remembering the original file name when gtroff uses an internal piping mechanism. The input file is not changed by this command. This command is a gtroff extension.

xf n s<line break>
The `f' stands for font.

Mount font position n (a non-negative integer) with font named s (a text word). See section 5.18.3 Font Positions.

xH n<line break>
The `H' stands for Height.

Set glyph height to n (a positive integer in scaled points `z'). AT&T troff uses the unit points (`p') instead. See section 8.1.4 Output Language Compatibility.

xi<line break>
The `i' stands for init.

Initialize device. This is the third command of the prologue.

xp<line break>
The `p' stands for pause.

Parsed but ignored. The original UNIX troff manual writes

 
pause device, can be restarted

xr n h v<line break>
The `r' stands for resolution.

Resolution is n, while h is the minimal horizontal motion, and v the minimal vertical motion possible with this device; all arguments are positive integers in basic units `u' per inch. This is the second command of the prologue.

xS n<line break>
The `S' stands for Slant.

Set slant to n (an integer in basic units `u').

xs<line break>
The `s' stands for stop.

Terminates the processing of the current file; issued as the last command of any intermediate troff output.

xt<line break>
The `t' stands for trailer.

Generate trailer information, if any. In gtroff, this is actually just ignored.

xT xxx<line break>
The `T' stands for Typesetter.

Set name of device to word xxx, a sequence of characters ended by the next white space character. The possible device names coincide with those from the groff `-T' option. This is the first command of the prologue.

xu n<line break>
The `u' stands for underline.

Configure underlining of spaces. If n is 1, start underlining of spaces; if n is 0, stop underlining of spaces. This is needed for the cu request in nroff mode and is ignored otherwise. This command is a gtroff extension.

xX anything<line break>
The `x' stands for X-escape.

Send string anything uninterpreted to the device. If the line following this command starts with a `+' character this line is interpreted as a continuation line in the following sense. The `+' is ignored, but a newline character is sent instead to the device, the rest of the line is sent uninterpreted. The same applies to all following lines until the first character of a line is not a `+' character. This command is generated by the gtroff escape sequence \X. The line-continuing feature is a gtroff extension.

8.1.2.5 Obsolete Command

In AT&T troff output, the writing of a single glyph is mostly done by a very strange command that combines a horizontal move and a single character giving the glyph name. It doesn't have a command code, but is represented by a 3-character argument consisting of exactly 2 digits and a character.

ddg
Move right dd (exactly two decimal digits) basic units `u', then print glyph g (represented as a single character).

In gtroff, arbitrary syntactical space around and within this command is allowed to be added. Only when a preceding command on the same line ends with an argument of variable length a separating space is obligatory. In AT&T troff, large clusters of these and other commands are used, mostly without spaces; this made such output almost unreadable.

For modern high-resolution devices, this command does not make sense because the width of the glyphs can become much larger than two decimal digits. In gtroff, this is only used for the devices X75, X75-12, X100, and X100-12. For other devices, the commands `t' and `u' provide a better functionality.

8.1.3 Intermediate Output Examples

This section presents the intermediate output generated from the same input for three different devices. The input is the sentence `hell world' fed into gtroff on the command line.

High-resolution device ps

This is the standard output of gtroff if no `-T' option is given.

 
shell> echo "hell world" | groff -Z -T ps

x T ps
x res 72000 1 1
x init
p1
x font 5 TR
f5
s10000
V12000
H72000
thell
wh2500
tw
H96620
torld
n12000 0
x trailer
V792000
x stop

This output can be fed into grops to get its representation as a PostScript file.

Low-resolution device latin1

This is similar to the high-resolution device except that the positioning is done at a minor scale. Some comments (lines starting with `#') were added for clarification; they were not generated by the formatter.

 
shell> echo "hell world" | groff -Z -T latin1

# prologue
x T latin1
x res 240 24 40
x init
# begin a new page
p1
# font setup
x font 1 R
f1
s10
# initial positioning on the page
V40
H0
# write text `hell'
thell
# inform about space, and issue a horizontal jump
wh24
# write text `world'
tworld
# announce line break, but do nothing because ...
n40 0
# ... the end of the document has been reached
x trailer
V2640
x stop

This output can be fed into grotty to get a formatted text document.

AT&T troff output
Since a computer monitor has a very low resolution compared to modern printers the intermediate output for the X Window devices can use the jump-and-write command with its 2-digit displacements.

 
shell> echo "hell world" | groff -Z -T X100

x T X100
x res 100 1 1
x init
p1
x font 5 TR
f5
s10
V16
H100
# write text with jump-and-write commands
ch07e07l03lw06w11o07r05l03dh7
n16 0
x trailer
V1100
x stop

This output can be fed into xditview or gxditview for displaying in X.

Due to the obsolete jump-and-write command, the text clusters in the AT&T troff output are almost unreadable.

8.1.4 Output Language Compatibility

The intermediate output language of AT&T troff was first documented in the UNIX troff manual, with later additions documented in A Typesetter-indenpendent TROFF, written by Brian Kernighan.

The gtroff intermediate output format is compatible with this specification except for the following features.

  • The classical quasi device independence is not yet implemented.

  • The old hardware was very different from what we use today. So the groff devices are also fundamentally different from the ones in AT&T troff. For example, the AT&T PostScript device is called post and has a resolution of only 720 units per inch, suitable for printers 20 years ago, while groff's ps device has a resolution of 72000 units per inch. Maybe, by implementing some rescaling mechanism similar to the classical quasi device independence, groff could emulate AT&T's post device.

  • The B-spline command `D~' is correctly handled by the intermediate output parser, but the drawing routines aren't implemented in some of the postprocessor programs.

  • The argument of the commands `s' and `x H' has the implicit unit scaled point `z' in gtroff, while AT&T troff has point (`p'). This isn't an incompatibility but a compatible extension, for both units coincide for all devices without a sizescale parameter in the `DESC' file, including all postprocessors from AT&T and groff's text devices. The few groff devices with a sizescale parameter either do not exist for AT&T troff, have a different name, or seem to have a different resolution. So conflicts are very unlikely.

  • The position changing after the commands `Dp', `DP', and `Dt' is illogical, but as old versions of gtroff used this feature it is kept for compatibility reasons.

8.2 Font Files

The gtroff font format is roughly a superset of the ditroff font format (as used in later versions of AT&T troff and its descendants). Unlike the ditroff font format, there is no associated binary format; all files are text files.@footnotegroff_194.html{Plan 9 troff has also abandoned the binary format. The font files for device name are stored in a directory `devname'. There are two types of file: a device description file called `DESC' and for each font f a font file called `f'.

8.2.1 `DESC' File Format  
8.2.2 Font File Format  

8.2.1 `DESC' File Format

The `DESC' file can contain the following types of line. Except for the charset keyword which must comes last (if at all), the order of the lines is not important.

res n
There are n machine units per inch.

hor n
The horizontal resolution is n machine units.

vert n
The vertical resolution is n machine units.

sizescale n
The scale factor for point sizes. By default this has a value of 1. One scaled point is equal to one point/n. The arguments to the unitwidth and sizes commands are given in scaled points. See section 5.19.2 Fractional Type Sizes, for more information.

unitwidth n
Quantities in the font files are given in machine units for fonts whose point size is n scaled points.

prepro program
Call program as a preprocessor. Currently, this keyword is used by groff with option `-Thtml' only.

postpro program
Call program as a postprocessor. For example, the line

 
postpro grodvi

in the file `devdvi/DESC' makes groff call grodvi if option `-Tdvi' is given (and `-Z' isn't used).

tcommand
This means that the postprocessor can handle the `t' and `u' intermediate output commands.

sizes s1 s2 ... sn 0
This means that the device has fonts at s1, s2, ... sn scaled points. The list of sizes must be terminated by 0 (this is digit zero). Each si can also be a range of sizes m-n. The list can extend over more than one line.

styles S1 S2 ... Sm
The first m font positions are associated with styles S1 ... Sm.

fonts n F1 F2 F3 ... Fn
Fonts F1 ... Fn are mounted in the font positions m+1, ..., m+n where m is the number of styles. This command may extend over more than one line. A font name of 0 means no font is mounted on the corresponding font position.

family fam
The default font family is fam.

use_charnames_in_special
This command indicates that gtroff should encode special characters inside special commands. Currently, this is only used by the HTML output device. See section 5.31 Postprocessor Access.

papersize string ...
Select a paper size. Valid values for string are the ISO paper types A0-A7, B0-B7, C0-C7, D0-D7, DL, and the US paper types letter, legal, tabloid, ledger, statement, executive, com10, and monarch. Case is not significant for string if it holds predefined paper types. Alternatively, string can be a file name (e.g. `/etc/papersize'); if the file can be opened, groff reads the first line and tests for the above paper sizes. Finally, string can be a custom paper size in the format length,width (no spaces before and after the comma). Both length and width must have a unit appended; valid values are `i' for inches, `C' for centimeters, `p' for points, and `P' for picas. Example: 12c,235p. An argument which starts with a digit is always treated as a custom paper format. papersize sets both the vertical and horizontal dimension of the output medium.

More than one argument can be specified; groff scans from left to right and uses the first valid paper specification.

pass_filenames
Tell gtroff to emit the name of the source file currently being processed. This is achieved by the intermediate output command `F'. Currently, this is only used by the HTML output device.

print program
Use program as a spooler program for printing. If omitted, the `-l' and `-L' options of groff are ignored.

charset
This line and everything following in the file are ignored. It is allowed for the sake of backwards compatibility.

The res, unitwidth, fonts, and sizes lines are mandatory. Other commands are ignored by gtroff but may be used by postprocessors to store arbitrary information about the device in the `DESC' file.

Here a list of obsolete keywords which are recognized by groff but completely ignored: spare1, spare2, biggestfont.

8.2.2 Font File Format

A font file, also (and probably better) called a font description file, has two sections. The first section is a sequence of lines each containing a sequence of blank delimited words; the first word in the line is a key, and subsequent words give a value for that key.

name f
The name of the font is f.

spacewidth n
The normal width of a space is n.

slant n
The glyphs of the font have a slant of n degrees. (Positive means forward.)

ligatures lig1 lig2 ... lign [0]
Glyphs lig1, lig2, ..., lign are ligatures; possible ligatures are `ff', `fi', `fl', `ffi' and `ffl'. For backwards compatibility, the list of ligatures may be terminated with a 0. The list of ligatures may not extend over more than one line.

special
The font is special; this means that when a glyph is requested that is not present in the current font, it is searched for in any special fonts that are mounted.

Other commands are ignored by gtroff but may be used by postprocessors to store arbitrary information about the font in the font file.

The first section can contain comments which start with the `#' character and extend to the end of a line.

The second section contains one or two subsections. It must contain a charset subsection and it may also contain a kernpairs subsection. These subsections can appear in any order. Each subsection starts with a word on a line by itself.

The word charset starts the character set subsection.@footnotegroff_196.html{This keyword is misnamed since it starts a list of ordered glyphs, not characters. The charset line is followed by a sequence of lines. Each line gives information for one glyph. A line comprises a number of fields separated by blanks or tabs. The format is

name metrics type code [entity-name] [-- comment]

name identifies the glyph name@footnotegroff_196.html{The distinction between input, characters, and output, glyphs, is not clearly separated in the terminology of groff; for example, the char request should be called glyph since it defines an output entity.: If name is a single character c then it corresponds to the gtroff input character c; if it is of the form `\c' where c is a single character, then it corresponds to the special character \[c]; otherwise it corresponds to the special character `\[name]'. If it is exactly two characters xx it can be entered as `\(xx'. Note that single-letter special characters can't be accessed as `\c'; the only exception is `\-' which is identical to \[-].

gtroff supports 8-bit input characters; however some utilities have difficulties with eight-bit characters. For this reason, there is a convention that the entity name `charn' is equivalent to the single input character whose code is n. For example, `char163' would be equivalent to the character with code 163 which is the pounds sterling sign in the ISO Latin-1 character set. You shouldn't use `charn' entities in font description files since they are related to input, not output. Otherwise, you get hard-coded connections between input and output encoding which prevents use of different (input) character sets.

The name `---' is special and indicates that the glyph is unnamed; such glyphs can only be used by means of the \N escape sequence in gtroff.

The type field gives the glyph type:

1
the glyph has a descender, for example, `p';

2
the glyph has an ascender, for example, `b';

3
the glyph has both an ascender and a descender, for example, `('.

The code field gives the code which the postprocessor uses to print the glyph. The glyph can also be input to gtroff using this code by means of the \N escape sequence. code can be any integer. If it starts with `0' it is interpreted as octal; if it starts with `0x' or `0X' it is interpreted as hexadecimal. Note, however, that the \N escape sequence only accepts a decimal integer.

The entity-name field gives an ASCII string identifying the glyph which the postprocessor uses to print the gtroff glyph name. This field is optional and has been introduced so that the HTML device driver can encode its character set. For example, the glyph `\[Po]' is represented as `&pound;' in HTML 4.0.

Anything on the line after the entity-name field resp. after `--' will be ignored.

The metrics field has the form:

 
width[,height[,depth[,italic-correction
  [,left-italic-correction[,subscript-correction]]]]]

There must not be any spaces between these subfields (it has been split here into two lines for better legibility only). Missing subfields are assumed to be 0. The subfields are all decimal integers. Since there is no associated binary format, these values are not required to fit into a variable of type `char' as they are in ditroff. The width subfield gives the width of the glyph. The height subfield gives the height of the glyph (upwards is positive); if a glyph does not extend above the baseline, it should be given a zero height, rather than a negative height. The depth subfield gives the depth of the glyph, that is, the distance from the baseline to the lowest point below the baseline to which the glyph extends (downwards is positive); if a glyph does not extend below the baseline, it should be given a zero depth, rather than a negative depth. The italic-correction subfield gives the amount of space that should be added after the glyph when it is immediately to be followed by a glyph from a roman font. The left-italic-correction subfield gives the amount of space that should be added before the glyph when it is immediately to be preceded by a glyph from a roman font. The subscript-correction gives the amount of space that should be added after a glyph before adding a subscript. This should be less than the italic correction.

A line in the charset section can also have the format

 
name "

This indicates that name is just another name for the glyph mentioned in the preceding line.

The word kernpairs starts the kernpairs section. This contains a sequence of lines of the form:

 
c1 c2 n

This means that when glyph c1 appears next to glyph c2 the space between them should be increased by n. Most entries in the kernpairs section have a negative value for n.

9. Installation

A. Copying This Manual

A.1 GNU Free Documentation License  License for copying this manual.

A.1 GNU Free Documentation License

Version 1.1, March 2000

 
Copyright (C) 2000 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA  02111-1307, USA

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.

  1. PREAMBLE

    The purpose of this License is to make a manual, textbook, or other written document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

    This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

    We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

  2. APPLICABILITY AND DEFINITIONS

    This License applies to any manual or other work that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you".

    A "Modified Version" of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

    A "Secondary Section" is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (For example, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

    The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License.

    The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License.

    A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, whose contents can be viewed and edited directly and straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup has been designed to thwart or discourage subsequent modification by readers is not Transparent. A copy that is not "Transparent" is called "Opaque".

    Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML designed for human modification. Opaque formats include PostScript, PDF, proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML produced by some word processors for output purposes only.

    The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

  3. VERBATIM COPYING

    You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

    You may also lend copies, under the same conditions stated above, and you may publicly display copies.

  4. COPYING IN QUANTITY

    If you publish printed copies of the Document numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

    If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

    If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a publicly-accessible computer-network location containing a complete Transparent copy of the Document, free of added material, which the general network-using public has access to download anonymously at no charge using public-standard network protocols. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

    It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

  5. MODIFICATIONS

    You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

    1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.

    2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has less than five).

    3. State on the Title page the name of the publisher of the Modified Version, as the publisher.

    4. Preserve all the copyright notices of the Document.

    5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.

    6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.

    7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.

    8. Include an unaltered copy of this License.

    9. Preserve the section entitled "History", and its title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.

    10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.

    11. In any section entitled "Acknowledgments" or "Dedications", preserve the section's title, and preserve in the section all the substance and tone of each of the contributor acknowledgments and/or dedications given therein.

    12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.

    13. Delete any section entitled "Endorsements". Such a section may not be included in the Modified Version.

    14. Do not retitle any existing section as "Endorsements" or to conflict in title with any Invariant Section.

    If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

    You may add a section entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

    You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

    The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

  6. COMBINING DOCUMENTS

    You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice.

    The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

    In the combination, you must combine any sections entitled "History" in the various original documents, forming one section entitled "History"; likewise combine any sections entitled "Acknowledgments", and any sections entitled "Dedications". You must delete all sections entitled "Endorsements."

  7. COLLECTIONS OF DOCUMENTS

    You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

  8. AGGREGATION WITH INDEPENDENT WORKS

    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, does not as a whole count as a Modified Version of the Document, provided no compilation copyright is claimed for the compilation. Such a compilation is called an "aggregate", and this License does not apply to the other self-contained works thus compiled with the Document, on account of their being thus compiled, if they are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one quarter of the entire aggregate, the Document's Cover Texts may be placed on covers that surround only the Document within the aggregate. Otherwise they must appear on covers around the whole aggregate.

  9. TRANSLATION

    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License provided that you also include the original English version of this License. In case of a disagreement between the translation and the original English version of this License, the original English version will prevail.

  10. TERMINATION

    You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

  11. FUTURE REVISIONS OF THIS LICENSE

    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

A.1.1 ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

 
  Copyright (C)  year  your name.
  Permission is granted to copy, distribute and/or modify this document
  under the terms of the GNU Free Documentation License, Version 1.1
  or any later version published by the Free Software Foundation;
  with the Invariant Sections being list their titles, with the
  Front-Cover Texts being list, and with the Back-Cover Texts being list.
  A copy of the license is included in the section entitled ``GNU
  Free Documentation License''.

If you have no Invariant Sections, write "with no Invariant Sections" instead of saying which ones are invariant. If you have no Front-Cover Texts, write "no Front-Cover Texts" instead of "Front-Cover Texts being list"; likewise for Back-Cover Texts.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

B. Request Index

Requests appear without the leading control character (normally either `.' or `'').

Jump to:   A   B   C   D   E   F   H   I   K   L   M   N   O   P   R   S   T   U   V   W  

Index Entry Section

A
ab]5.34 Debugging
ad]5.8 Manipulating Filling and Adjusting
af5.7.4 Assigning Formats
aln5.7.1 Setting Registers
als5.20 Strings
am5.22 Writing Macros
am15.22 Writing Macros
ami5.22 Writing Macros
as1]5.20 Strings
as]5.20 Strings
asciify5.26 Diversions

B
backtrace5.34 Debugging
bd]5.18.6 Artificial Fonts
bd]5.18.6 Artificial Fonts
blm5.25.4 Blank Line Traps
box5.26 Diversions
boxa5.26 Diversions
bp]5.17 Page Control
bppage5.17 Page Control
bppage5.17 Page Control
br5.8 Manipulating Filling and Adjusting
break5.21.3 while
brp5.8 Manipulating Filling and Adjusting

C
c2]5.12 Character Translations
cc]5.12 Character Translations
ce]

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  Copyright 2003   by The Free Software Foundation     Updated Jun 2003