sub pad{
        my ($string, $length)=@_;
        my $padlength=$length-length($string);
        return "0"x$padlength.$string;
} 
print pad("123",5);
print "\n";

print pad("123",6);
print "\n";
[download]

This prints out:
00123
000123

vroom | Tim Vroom | vroom@cs.hope.edu