#!/usr/bin/env perl

use strict;
use warnings;

# Only arguments '--exclusive 1' exactly are supported.
(@ARGV == 2) or die;
my $mode = shift;
($mode eq "--exclusive") or die;
my $fd = shift;
($fd eq "1") or die;

use Fcntl ':flock';

open(my $fh, '>&=', 1) or die "open: $!";

flock($fh, LOCK_EX) or die "flock: $!";