grinder's solution works for me (grinder++). Here's my test against your strings.. 
#!/usr/bin/perl
use strict;
use warnings;

my @strings = qw/aaa_gjh1_dfgdf_0009 aaa_gjh_0000 00000 aaa_fdsfs_000 
+aaa_sdf_jdsh_01111/;

print is_valid($_) ? '' : "no ", "match: $_\n" for @strings;

sub is_valid {
    my $test = shift;
    return $test =~ /\Aaaa_\w{1,24}(?<=\D)\d{4}\z/;
}

[download]

In reply to Re^2: Number of digits at the end of the string by rowdog
in thread Number of digits at the end of the string by isha

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