A cheap hack, but will depend on how your OS operates:      if (-d "/proc/$pid") { ... } This will likely work with most UNIX variants. As a bonus, you can examine the command line parameters of that process to see if it's the one you were expecting. On Linux, at least, this is available in a pseudo-file:

    sub GetProcessCommand
    {
            my ($pid) = @_;

            return (open (PID, "/proc/$pid/cmdline") && <PID>);
    }
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This way you can validate the "authenticity" of the process¹:

    # Check for buddy named 'xyz-proc'
    if (GetProcessCommand($pid) =~ /xyz\-proc/) { ... }
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Sometimes you will find a process active in that slot, but for some reason it isn't yours.

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1. This "authentication" is pretty loose, so be sure to check the owner of the process too. You can masquerade your process as anything you like by setting $0, after all, but you can't change the uid of the process so easily.