As others have said, you should use a module if you can. However, if you can't, you might be able to use the unix 'md5sum' command - it's available at least on my RH6.2 box. If you do have that command, then something like this would work:

#!/usr/bin/perl -w
use strict;
my $md5;

while (<>) {
  chomp;
  $md5 = `echo $_ | md5sum`;
  $md5 =~ s/ .*//;
  print "$_ -> $md5";
}
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-- Dan