You have not given enough context to say what is happening. For example, you say "the 'run' button hangs". What does that mean? Is this a Tk application?

The code: exec() unless fork() is not robust. If fork() fails, it returns undef. In this case your code is going to do an exec in the main process and not give an error. You really shouldn't try to write a one-liner here because there are three cases (1) parent (2) child (3) fork failed.

One general-purpose debugging technique:

# do this once (obviously, I hope)
use IO::File;
open LOG, ">>log.out" or die "opening log.out: $!\n";
LOG->autoflush(1);
printf LOG "PROC $$: %d %s run starts %s\n",
   time, __FILE__, scalar(localtime);

# put lots of these throughout your program
printf LOG "PROC $$: %d %s(%d)\n", time, __FILE__, __LINE__;

[download]
If you look at the times, you can see where your program is waiting. Scatter these liberally through your program. You may be surprised.

In reply to Re: It works, and then it doesn't...connecting to a daemon over the net by Thelonius
in thread It works, and then it doesn't...connecting to a daemon over the net by seaver

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