$ perle 'my $x = "1 12 123"; while ($x =~ /(\d+)\s*/g) { say $1 }'
1
12
123
$ perle 'my $x = "1_12_123"; while ($x =~ /(\d+)\s*/g) { say $1 }'
1
12
123
$ perle 'my $x = "1_12_123"; while ($x =~ /(\d+)/g) { say $1 }'
1
12
123