How can I tell at run time that my script is writing to STDERR?

Dave05 has asked for the wisdom of the Perl Monks concerning the following question: ⭐ (debugging)

Replies are listed 'Best First'.
Re: How can I tell at run time that my script is writing to STDERR?⭐ by zigdon (Deacon) on Oct 23, 2002 at 16:27 UTC
use the $SIG{__WARN__}: `$SIG{__WARN__} = sub { die $_[0] }; warn "This will be fatal\n"; print "You will never get to this line\n";` [download] See perlvar for more info.	[reply] [d/l]
Re: How can I tell at run time that my script is writing to STDERR? by rir (Vicar) on Oct 23, 2002 at 17:54 UTC
Zigdon's answer is perfectly correct. So this is offered as a more generalized solution. Just override the offending function like so: `use subs qw( warn); sub warn { die @_} warn "This is a warning"; print "NOT REACHED\n";` [download]	[reply] [d/l]
Re: How can I tell at run time that my script is writing to STDERR? by Dave05 (Beadle) on Oct 23, 2002 at 15:05 UTC
To partially answer myself, for most warnings, saying `use warnings FATAL => 'all';` will have the desired effect. However, this won't kill my program if I issue a warning using 'warn'	[reply] [d/l]
Re: How can I tell at run time that my script is writing to STDERR? by Dave05 (Beadle) on Oct 24, 2002 at 10:06 UTC
Many thanks. I've tested both solutions. Note that zigdon's solution will trap warnings issued by included modules, whereas rir's solution will only affect calls to `warn` within the package where the sub is declared.	[reply] [d/l]
Re: How can I tell at run time that my script is writing to STDERR? by mystik (Sexton) on Oct 24, 2002 at 15:21 UTC
The title is confuzing -- I was about to state that the solutions listed don't really trap all of output to STDERR , one can still do: `print STDERR "the one that got away\n";` [download] (Unfortunatly, I don't know a good solution to this instance...)	[reply] [d/l]
Re: How can I tell at run time that my script is writing to STDERR? by .tom. (Initiate) on Oct 25, 2002 at 11:43 UTC
What you can do to prevent anything from beeing to STDERR is close the file descriptor : `print STDERR "prints...\n"; close(STDERR); print STDERR "doesn't print...\n" or print "this was bound to fail\n";` [download] But any entity that tries to write to STDERR will fail doing that, so you should also reopen STDERR to /dev/null to avoid that. `open(STDERR,'>/dev/null'); print STDERR "doesn't fail so this..." or print "...won't print";` [download]	[reply] [d/l] [select]