I have used Proc::PID::File and find it very easy to use: 
use Proc::PID::File;
die "Already running!" if Proc::PID::File->running();

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No matter how great and destructive your problems may seem now, remember, you've probably only seen the tip of them. [1]

In reply to Re: Abort if instance already running? by andreas1234567
in thread Abort if instance already running? by pileofrogs

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