#!/usr/bin/perl
use strict;
use warnings;

# Read the regexes
my @Rexes;
while (my $t=<DATA>) {
	chomp $t;
	last if $t=~/^$/;
	my ($regex, $repl) = split /\t+/, $t;
	push @Rexes, [ qr($regex), $repl ];
}

# Process the text
while (my $l = <DATA>) {
	$l=~s/$$_[0]/$$_[1]/eg for @Rexes;
	print $l;
}

__DATA__
duck		cluck
a(b+)c		c$1a

That bird says "duck!"
xyzzy plugh ac abc abbc abbbc