#!/usr/bin/perl -w
use strict;
BEGIN {*CORE::GLOBAL::flock = sub {die} };
open(I,'>test.pm') or die $!;
print I <<'EOS';
    package test;
    use strict;
    use warnings;
    use constant HAS_FLOCK => eval { flock STDOUT, 0; 1 };
    print "no flock" unless HAS_FLOCK;
    1;
EOS
close I;
require "test.pm";

__END__