#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11150123
use warnings;

my $blockoftext = <<END;
mouse
cat
1
2
3
^cat
deer
eel
cat
furbaby
elk
^cat
dog
fish
END

$blockoftext =~ s/^cat.*?^\^cat/
  my $catsection = $&;
  $catsection =~ s!^!#!gm;
  $catsection
  /gems;

print $blockoftext;