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GNU macro processor

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7.1 Deleting whitespace in input

The builtin dnl reads and discards all characters, up to and including the first newline:

 
dnl
and it is often used in connection with define, to remove the newline that follow the call to define. Thus

 
define(`foo', `Macro `foo'.')dnl A very simple macro, indeed.
foo
=>Macro foo.

The input up to and including the next newline is discarded, as opposed to the way comments are treated (see section 2.4 Comments).

Usually, dnl is immediately followed by an end of line or some other whitespace. GNU m4 will produce a warning diagnostic if dnl is followed by an open parenthesis. In this case, dnl will collect and process all arguments, looking for a matching close parenthesis. All predictable side effects resulting from this collection will take place. dnl will return no output. The input following the matching close parenthesis up to and including the next newline, on whatever line containing it, will still be discarded.


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