I'm not so sure whether I grasp the correct connotation of 'match' in that context. But, consider using: 

use strict;
use warnings;

my $str = 'abc' x 10;

if (length $str == 30) {
    print "\$str has length of 30\n";
}

[download]
or 
print $str =~ /(.{30})/;

[download]

Former one succeeds if $str has a length of 30 characters. Latter one yields back the first 30 characters extracted from $str using a regular expression.

In reply to Re: matching a defined lenght by shigetsu
in thread matching a defined lenght by harryC

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