Re^3: Cron Jobs That Run For Too Long

[adamk]

But wait, it gets better again!

You know how you can have that nifty __DATA__ block at the end of your script? It turns out you can lock that too :)

I've used this a number of times and it works just great.

#!/usr/bin/perl

use strict;
use Fcntl 'LOCK_EX', 'LOCK_NB';

unless ( flock DATA, LOCK_EX | LOCK_NB ) {
    print STDERR "Found duplicate script run. Stopping\n";
    exit(0);
}

...

1;





### DO NOT REMOVE THE FOLLOWING LINES ###

__DATA__
This exists to allow the locking code at the beginning of the file to work.
DO NOT REMOVE THESE LINES!

[LanX]

(For the record if someone reads this thread again)

Cool trick, but strongly discouraged on Windows.

See Re^2: File lock demo and other links in that thread for explanation.

[Bod]

but strongly discouraged on Windows

Good point...
But the OP did mention CRON and not Task Scheduler.

[LanX]

This trick was referenced many times in the following years, and many people won't bother to read the OP.

And personally I take "cron" as a generic term and I've also already seen people installing a cron demon on Win.

[astroboy]

hey, that's really nice.

[Anonymous Monk]

this works great!!! can you give explenations on the __DATA__ part? I dont have a clue what is this for... Roy

[marto]

See The __DATA__ token, from SelfLoader. perldoc is your friend.

Martin

[Anonymous Monk]

11 years later this is still brilliant.