make your crontab entry something resembling 
foobar.pl 2>/path/to/my/stderr.txt

[download]
or you could 
open STDERR, '>', '/path/to/my/stderr.txt';

[download]
although that might not work for processes you exec/system

In reply to Re: Capturing STDERR to a variable by Anonymous Monk
in thread Capturing STDERR to a variable by oron

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