FAQ 6.10 How do I use a regular expression to strip C style comments from a file?

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6.10: How do I use a regular expression to strip C style comments from a file?

    While this actually can be done, it's much harder than you'd think. For
    example, this one-liner

        perl -0777 -pe 's{}gs' foo.c

    will work in many but not all cases. You see, it's too simple-minded for
    certain kinds of C programs, in particular, those with what appear to be
    comments in quoted strings. For that, you'd need something like this,
    created by Jeffrey Friedl and later modified by Fred Curtis.

        $/ = undef;
        $_ = <>;
$2 ? $2 : ""#gse;

    This could, of course, be more legibly written with the "/x" modifier,
    adding whitespace and comments. Here it is expanded, courtesy of Fred

           /\*         ##  Start of /* ... */ comment
           [^*]*\*+    ##  Non-* followed by 1-or-more *'s
           )*          ##  0-or-more things which don't start with /
                       ##    but do end with '*'
           /           ##  End of /* ... */ comment

         |         ##     OR  various things which aren't comments:

             "           ##  Start of " ... " string
               \.           ##  Escaped char
             |               ##    OR
               [^"\]        ##  Non "\
             "           ##  End of " ... " string

           |         ##     OR

             '           ##  Start of ' ... ' string
               \.           ##  Escaped char
             |               ##    OR
               [^'\]        ##  Non '\
             '           ##  End of ' ... ' string

           |         ##     OR

             .           ##  Anything other char
             [^/"'\]*   ##  Chars which doesn't start a comment, string or
         }{defined $2 ? $2 : ""}gxse;

    A slight modification also removes C++ comments:

$2 ? $2 : ""#gse;


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