$ perl -E '
    my $re = qr{(\w+)\s+((?:\s*\d+)*)};
    my $str = "a 1 2 3 b 4 5 6";

    while ($str =~ /$re/g) {
        say "|$&|: |$1| |$2|";
    }
'
|a 1 2 3|: |a| |1 2 3|
|b 4 5 6|: |b| |4 5 6|