As long as you have line buffering, you should be OK.

see $| and IO::Handle::setvbuf If you use the default settings with syswrite you should be ok. If you are on a system where this does not work you can add an flock around the syswrite. 

BEGIN { $SIG{'__WARN__'} = sub { syswrite STDERR, $_[0] } }

warn "Warnings go to STDERR\n";

[download]

Update: added example.

-- gam3
A picture is worth a thousand words, but takes 200K.

In reply to Re: multiple programs sharing redirected STDERR by gam3
in thread multiple programs sharing redirected STDERR by ff

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