$ cat splok.pl
use strict;
use warnings;

my @regs = ('(x\d{3,}?)', '(x\d{3,}?x)', '(x\d{3,})',
             '(x\d{3})',   '(x\d{3,}x)',  '(x\d{3,}?x?)');
my @strs = ('xx', 'x12x', 'x123456x', 'x12x x123x', 'x123456y');

printf "%-12.12s ", $_ for " ", @regs;
print "\n";
for my $str (@strs) {
    printf "%-12.12s ", $str;
    for my $reg (@regs) {
        printf "%-12.12s ", ($str=~$reg) ? $1: '-nope-';
    }
    print "\n";
}

$ perl splok.pl
             (x\d{3,}?)   (x\d{3,}?x)  (x\d{3,})    (x\d{3})     (x\d{3,}x)   (x\d{3,}?x?)
xx           -nope-       -nope-       -nope-       -nope-       -nope-       -nope-
x12x         -nope-       -nope-       -nope-       -nope-       -nope-       -nope-
x123456x     x123         x123456x     x123456      x123         x123456x     x123
x12x x123x   x123         x123x        x123         x123         x123x        x123x
x123456y     x123         -nope-       x123456      x123         -nope-       x123