#!/usr/bin/perl -w
use strict;

while (<DATA>)
{
  my $number = (/(\d+)$/)[0]; #previous was \w+ oooops!
  print "$number\n" if defined $number;
    # "if defined" allows for blank lines, etc.
}

__DATA__
a.b.c.d=10
a.b.e.f=9999
a.f.g.h=456

#prints:
#10
#9999
#456