That's a good point Corion regarding locking $0. I updated the code by not appending the suffix ".lock" when path is given. The lock is released automatically upon termination of the script.

use Mutex::Flock;

( my $mutex = Mutex::Flock->new( path => $0 ) )->lock_exclusive;

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Another way, with the timewait method.

my $mutex = MCE::Mutex::Flock->new( path => $0 );

# terminate script if a previous instance is still running
exit unless $mutex->timedwait(2);

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The module is beneficial regarding supporting threads and processes. I will make time to complete it and subsequently a release for CPAN.

Regards, Mario

Edit: Added timedwait example.