#!/usr/bin/perl -w

use strict;

my %keywords = ( foo=>'/foo.html',
		bar=>'bar.html',
		cult=>'http://perlmonks.org'
		);
my $textfile ="/file/to/link";
open TEXTFILE, $textfile or die "Yikes! $textfile won't open: $!\n";

my $data;
{
	local $/; 	#sets input list separator to undef
			#so we can 'slurp' the file in
	$data = <TEXTFILE>;
}

close TEXTFILE;

foreach (keys %keywords) {
		my $url = $keywords{$_};
		# EDITED ... I'd forgotten to escape 
		# the / in front of the closing <a> 
		# credit to Albannach
		$data =~ s/($_)/<a href="$url">$1<\/a>/g;
}
# now do something with $data