#!/usr/bin/perl
use warnings;
use strict;

while (<DATA>) {
    if (my ($alnum, $constrained)
        = /^foo          # "foo"
           _             # followed by "underscore"
           (?:bar|test)  # followed by "bar|test" (bar or test)
           _             # followed by "underscore"

           ((?:\w+\.)+?) # followed by alhpnum string with
                         # dot at end (like foo10.1.1.1)

           \1?           # followed by one or zero occurences
                         # of same alhpnum string (like
                         # foo10.1.1.1) followed by dot

           (\w{1,10})    # followed by 1-10 characters,
                         # containing at least one digit and
                         # one letter and underscore (e.g.
                         # TEST_test, TEST_test2,
                         # TEST1_test2)

           \.txt$        # ends with .txt
          /x) {

        print "<$alnum | $constrained> $. ok\n"
            if 3 == grep $constrained =~ $_,
                qr/_/, qr/\d/, qr/[[:alpha:]]/;
    }
}
__DATA__
foo_bar_foo10.1.1.1.TEST.txt
foo_test_foo10.1.1.1.foo10.1.1.1.TEST_test.txt
foo_test_foo10.1.1.1.foo10.1.1.1.txt
foo_test_foo10.1.1.1.foo10.1.1.1.TEST-1.txt
foo_test_foo10.1.1.1.foo10.1.1.1.TEST_1.txt
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Note that I changed the quantifier in the first capturing group to frugal to avoid matching both occurrences of $alnum as one without repetition. Nevertheless, in the third case, the whole substring foo10.1.1.1.foo10.1.1. corresponds to $alnum, it's not repeated, and $constrained is just 1 .

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]