It may also be useful to check the return status of your qx command using the special variable $?. This may be a more portable solution since I do not get the same system message as you do when it fails. I get "id: test: No such user".

use strict;
use warnings;

my $cmd = qx{id ahmedf 2>&1};
if ($?) {
    print "Please check LDAP\n";
    exit 2;
}
elsif ($cmd =~ /uid/) {
    print "LDAP Ok\n";
    exit 0;
}
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