#!/usr/local/bin/perl
use strict;
use warnings;
use String::Interpolate qw(safe_interpolate);

# 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/$$_[0]/safe_interpolate($$_[1])/eg for @Rexes;
    print $l, "\n";
}

__DATA__
duck	cluck
a(b+)c	\uc${1}\ua

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