in reply to Regex to match 20 chars of some digits followed by some spaces

Some collegues are first to the punch

mildside has

m/^\d((?<=\d)\d(?=([ \d]|$))|(?<=[\d ]) (?=( |$))){19}$/
another is
m/^(?=\d*(?:\d ) *(?!\d)$)[0-9 ]{20}$/

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