$ perle 'my $x = "1 12 123"; while ($x =~ /^(\d+)/g) { say $1 }'
1
$ perle 'my $x = "1 12 123"; while ($x =~ /(\d+)$/g) { say $1 }'
123
$ perle 'my $x = "1 12 123"; while ($x =~ /^(\d+)$/g) { say $1 }'
$