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

my %dictionary = (foo => 'bar',
                  baz => 'w00t');

sub replace {
    my $str = shift;
    $str =~ m[(<[^>]+>)?([^<]+)(</[^>]+>)?(.*)];
                        # the key should never contain '<'

    my $key    = $2 . $4;
    my @tags   = ($1, $3);
    my $length = length $2;
    $key =~ s[$_][$dictionary{$_}] for keys %dictionary;
    if (grep $_, @tags) { # return tags to replaced string
        substr $key, $length, 0, $tags[1];
        substr $key, 0, 0, $tags[0];
    }
    return $key;
}

use Test::More;

is replace('baz'), 'w00t';
is replace('<tag>f</tag>oo'), '<tag>b</tag>ar';
is replace('<b>fo</b>o'), '<b>ba</b>r';

done_testing();