#!/usr/bin/perl
use strict;
use warnings;
use Fcntl qw(:DEFAULT :flock);

my $sec = 30;

print 'Please type the file that I should lock for
$sec: ';
my $file = <STDIN>;
chomp $file;
sysopen( FH, $file, O_RDWR ) or die "Cannot edit
$file: $!\n";
flock( FH, LOCK_EX ) or die "Cannot lock $file: $!\n";
 
print 'Ok, holding the file for $sec seconds. I will
not change anythingin the file', "\n";
sleep $sec;

close(FH);
 
print "Finished\n";