#!/usr/bin/perl

use 5.020;
use experimental 'signatures';
use Test::More;

sub digits( $S, $pos ) {
    pos($S) = $pos;
    return ($S =~ m/\b(\d*\G\d*)\b/c) ? $1 : undef;
}

is digits( 'Hello World 123456 !!! 789 ...', 14 ), '123456', "In middle";
is digits( '12345 World 123456 !!! 789 ...', 14 ), '123456', "No digits before";
is digits( '12345 World 123456 !!! 789 ...', 17 ), '123456', "At end";
is digits( '12345 World 123456 !!! 789 ...', 12 ), '123456', "At start";

done_testing;