why don't you substitute before printing ?????

   $file2 = param('file'); # A windows path is supposed to be filled h
+ere (c:/foo/bar.txt)
   $file2 =~ s%\\%/%g; # It's not too late to substitute here.
   $file2 =~ s%.*:%%;  # also cut off c:
   print "$file2\n"; # c:foobar.txt is printed
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if you need to keep the original value you can do

   ($file3 = $file2) =~ s%what%ever%g;
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