I think I understand your editing a file instructions, and if so I was really over-complicating things trying to do an "in place" replacement. Now I am trying something like this: 
 
open FH, "<infile.txt" or die $!;
open OUT, ">outfile.txt";
while (<FH>)
          {
          if (/(\S+):(\S+).*\n/)
               {
               $var1 = "$1";
               $var2 = "$2";
               print OUT "$var1_$var2\n"
               }
            elsif (/(.*)\n/)
                {
                print OUT "$1\n";
               }
            }
     close FH;

[download]

This does what I want in terms of preserving the input files non matching lines, but I am still getting a "use of uninitialized value" error, one for every line in the input file:

Use of uninitialized value $var1_ in concatenation (.) or string at test_perl.pl line 42

In reply to Re^2: In place search and replace with a hash by hkates
in thread In place search and replace with a hash by hkates

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