use strict;
use warnings;

open FILE, ">x.txt" or die "Cannot create test file: $!";
print FILE "TEXT\n";
close FILE;

my $pid = fork();
if ($pid == 0) {
    # in the child
    open FC, "<x.txt" or die "Can not open test file";
    if (flock(FC, 2) < 0) { die "Can not lock" }
    for (0..10) {
        sleep 1;
        print "$_\n";
        die "No lock" if ! -s "x.txt";
    }
    close FC;
} else {
    sleep 5;
    open FC2, ">x.txt" or print "Can not create file\n";
    close FC2;
    sleep(5);
}