Here's my shot at it:

#!/usr/bin/perl

use strict;
use warnings;

my $string = 'perl monks';
my $space = qr/\s/;

for (0 .. (length $string) - 2) {
    my $match = substr($string,$_,2);
    next if ($match =~ $space);
    print "$match\n";
}
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Added: This thread shows that TIMTOWDI is alive and well!