#! /usr/local/bin/perl -w

use strict;
use Regexp::Assemble;

my $re = Regexp::Assemble->new(track => 1)
    # remember to double up your backslashes
    ->add( '^X\\d+' )
    ->add( '^X\\d\\d*' )
    ->add( '^\\s*X\\d\\d*' )
    ->add( '^X\\d\\d' )
    ->add( '^X\\d' )
;

while( <DATA> ) {
    chomp;
    print $re->matched, " matched <$_>\n" if $re->match($_);
}

__DATA__
XY1
X234
X56
X4
Z0
 X77

##</code><code>##

^X\d\d* matched <X234>
^X\d\d* matched <X56>
^X\d\d* matched <X4>
^\s*X\d\d* matched < X77>