use warnings; use strict;

use Getopt::Long
  qw(:config
      gnu_compat no_ignore_case
      no_debug
    );

#  Get regexen|strings for substitution.
my ($in ,  $out);
GetOptions( 'i|in=s' => \$in , 'o|out=s' => \$out) or usage();
usage() unless defined $in && defined $out;

printf "in: '%s'  out: '%s'\n" , $in , $out;

my $text;
while (<STDIN>) { $text .= $_; }
chomp $text;

printf "before:\n'%s'\n" , $text;

$text =~ s/$in/$out/g;

printf "after:\n'%s'\n" , $text;

sub usage { die "specify strings for -in & -out options.\n"; }