Hm, your exact request is vague. To extract a list of digits from a data stream, I suggest one of the following:

my $variable = '12345(checkthis)';
my @digits; undef @digits;

while ($variable =~ /\d/g) {  push @digits, $& }
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my $variable  = '12345(checkthis)';
my @digits; undef @digits;

foreach (split '', $variable) {  push @digits, $_ if /\d/ }
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Each case will result in a list of digits stored in @digits