If you are going to pipe it to a script, then I believe it has to be in another script.

If all you need to do is write STDERR to a file, why not just do this at the beginning of your script: 
open(STDERR, '>error.txt');

[download]
Update:Try using IO::Tee, like suggested by Roy Johnson. I included a sample in my reply to you below.

- Tom

In reply to Re: Open pipe to a function? by tcf22
in thread Open pipe to a function? by Sprad

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