Regular expressions can be used in cfagent in connection with
editfiles and processes to search for lines matching
certain expressions. A regular expression is a generalized wildcard. In
cfagent wildcards, you can use the characters '*' and '?' to match any
character or number of characters. Regular expressions are more
complicated than wildcards, but have far more flexibility.
NOTE: the special characters `*' and `?'
used in wildcards do not have the
same meanings as regular expressions!.
Some regular expressions match only a single string. For example, every
string which contains no special characters is a regular expression
which matches only a string identical to itself. Thus the regular
expression `cfengine' would match only the string "cfengine", not
"Cfengine" or "cfengin" etc. Other regular expressions could match more
general strings. For instance, the regular expression `c*' matches
any number of c's (including none). Thus this expression would match the
empty string, "c", "cccc", "ccccccccc", but not "cccx".
Here is a list of regular expression special characters and operators.
`\'
The backslash character normally has a special purpose: either to
introduce a special command, or to tell the expression interpreter that
the next character is not to be treated as a special character.
The backslash character stands for itself only when protected by square
brackets [\] or quoted with a backslash itself `\\'.
`\b'
Matches word boundary operator.
`\B'
Match within a word (operator).
`\<'
Match beginning of word.
`\>'
Match end of word.
`\w'
Match a character which can be part of a word.
`\W'
Match a character which cannot be part of a word.
`any character'
Matches itself.
`.'
Matches any character
`*'
Match zero or more instances of the previous object. e.g. `c*'.
If no object precedes it, it represents a literal asterisk.
`+'
Match one or more instances of the preceding object.
`?'
Match zero or one instance of the preceding object.
`{ }'
Number of matches operator. `{5}' would match exactly 5
instances of the previous object. `{6,}' would match at least
6 instances of the previous object. `{7,12}' would match at least
7 instances of, but no more than 12 instances of the preceding object.
Clearly the first number must be less than the second to make a valid
search expression.
`|'
The logical OR operator, OR's any two regular expressions.
`[list]'
Defines a list of characters which are to be considered as a single
object (ORed). e.g. `[a-z]' matches any character in the range a to
z, `abcd' matches either a, b, c or d. Most characters are
ordinary inside a list, but there are some exceptions: `]' ends the
list unless it is the first item, `\' quotes the next character,
`[:' and `:]' define a character class operator (see below),
and `-' represents a range of characters unless it is the first
or last character in the list.
`[^list]'
Defines a list of characters which are NOT to be matched. i.e.
match any character except those in the list.
``[:class:]''
Defines a class of characters, using the ctype-library.
alnum
Alpha numeric character
alpha
An alphabetic character
blank
A space or a TAB
cntrl
A control character.
digit
0-9
graph
same as print, without space
lower
a lower case letter
print
printable characters (non control characters)
punct
neither control nor alphanumeric symbols
space
space, carriage return, line-feed, vertical tab and form-feed.
upper
upper case letter
xdigit
a hexadecimal digit 0-9, a-f
``( )''
Groups together any number of operators.
`\digit'
Back-reference operator (refer to the GNU regex documentation).
`^'
Match start of a line.
`$'
Match the end of a line.
Here is a few examples. Remember that some commands look for
a regular expression match of part of a string, while others
require a match of the entire string (see Reference manual).
^# match string beginning with the # symbol
^[^#] match string not beginning with the # symbol
^[A-Z].+ match a string beginning with an uppercase letter
followed by at least one other character
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