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

foreach my $url ("abgc100.html", "xyz1000.htMl", 
                 "qwer10.html",  "abc123.htm", "qrz12345.htm",
                 "something-12341234.html")
{
   my ($number) = $url =~ /(\d+)\.htm(l)?$/i;
   print "$number\n";
}

__END__
100
1000
10
123
12345
12341234