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


my @string = ( 
    'aaa_fgjkghd11__hfksdh11__0000', 'aaa_fgjkghd11_hfksdh11__0000',
    'aaa_fgjkghd11hfksdh11__0000',   'aaa_fgjkghd11__hfksdh11_0000',
    'aaa_fgjkghd11__hfksdh110000',   'aaa_fgjk__ghd11_hfksdh1_10000',
    'aaa_fgjk__ghd11_hfksdh1_0000',  'aa_fgjk__ghd11_hfksdh1_a000',
    'aaa_fgjk_ghd_11_hfksdh1_0000'
);

for (@string) {
    print /\A 
            a{3}
               [_] 
                 (?: [a-z0-9] | [^_][_] ){1,24}
               [^_][_] 
            \d{4} 
           \z
          /xms ? '   ' : 'no ';
    print "match : $_\n";
}


##</code><code>##

no match : aaa_fgjkghd11__hfksdh11__0000
no match : aaa_fgjkghd11_hfksdh11__0000
no match : aaa_fgjkghd11hfksdh11__0000
no match : aaa_fgjkghd11__hfksdh11_0000
no match : aaa_fgjkghd11__hfksdh110000
no match : aaa_fgjk__ghd11_hfksdh1_10000
no match : aaa_fgjk__ghd11_hfksdh1_0000
no match : aa_fgjk__ghd11_hfksdh1_a000
   match : aaa_fgjk_ghd_11_hfksdh1_0000