Problem:

You want to grep an entire C source code tree for comments and dump them to a text file, along with where you found them:

Solution:

#!/usr/bin/perl

#########################################################
# this script will grep out any "C-style" comments      #
# from a file.  C-Style being /* */ or //               #
#                                                       #
# usage: comment_grep                         #
#                                                       #
# to recursively traverse a directory with this:        #
# find ./ -name '*' -exec comment_grep {} > /tmp/foo \; #
#                                                       #
#########################################################

$infile = shift;

$/ = "";        # remove newline from the line delimiter

$found = 0;
while(<>)
{
#this pattern will match /* */ comments
   if(
      m{
      (/\*              # match the /*
      (?:[^*][^/])*     # match any number of characters that AREN'T */
      \*/)              # match the */
      }mx               # multi-line regex x option to allow comments
     )
   {
      unless($found)    # list what file you found this in
                        # , if you find anything 
      {
         print "\nfrom $infile:\n";
      }
      print "\n";     # print /* */ and anything in between
      $found = 1;
   }
# this pattern will match // comments
   if(
      m{
      (//.*\n)          # match // then anything, up to a newline
      }x                # x option to allow comments
     )
   {
      unless($found)    # list what file you found this in, if you
                        #    find anything.
      {
         print "\nfrom $infile:\n";
      }
      print "";       # print /* */ and anything in between
      $found = 1;
   }
}