I stumbled acros the following problem while writing code to characterize numbers. I want to capture those numbers that consists of runs of consecutive digits such as 123 or 4567 (any length > 1 and < 10). Of course there are many ways to do this, but I tried the following and it works nicely: 

#!perl

use strict;
use warnings;

while (<DATA>) {
    chomp($_);
    print "$_ okay\n" if /^(\d)((??{$+ + 1}))+$/;
}

__DATA__
234
213
12345

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with as output: 
234 okay
12345 okay

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as expected.

However, if I include use warnings; as I usually do, I get the following warning: 
((??{$+ + 1}))+ matches null string many times
before HERE mark in regex
m/^(\d)((??{$+ + 1}))+ << HERE $/
at ./test.pl line 8.

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Could anyone enlighten me as to (1) the source of the warning, and (2) how to reformulate the regexp to get rid of it?

I'm aware that the (??{...}) construct is experimental and won't use it in production code, but it triggers my curiosity.

Thanks in advance, -gjb-

In reply to Code in regexp by gjb

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