duplicating STDERR to a logfile...

cadphile has asked for the wisdom of the Perl Monks concerning the following question:

A simple question really: I want to capture the STDERR from commands like croak and cluck into a log file that records all output of my program. I've read the previous comments in Perl Monks and I find the following in the Camel book:

   use FileHandle;
   use Carp qw (cluck croak);

   my $LOG_FH = new FileHandle( "somefile", "w" );
   my $fileno = fileno $LOG_FH;
   open STDERR, ">&$fileno" or croak "Can't dup STDERR.";

   cluck "Testing the output of Carp commands.";
[download]

(I need to use the $fileno because the ">&" dup operation doesn't work on I/O typeglobs.)

This works fine: all STDERR after this goes into $LOG_FH, but it no longer goes to the terminal.

But what I want is like the command "tee". I want STDERR to go to the terminal window, AND to be duplicated into the $LOG_FH filehandle.

Any clues??

Thanks, -Cadphile

Comment on duplicating STDERR to a logfile... Download Code

Replies are listed 'Best First'.
Re: duplicating STDERR to a logfile... by Kanji (Parson) on May 08, 2002 at 21:54 UTC
IO::Tee (alt.) perhaps? --k.	[reply]
(RhetTbull) Re: duplicating STDERR to a logfile... by RhetTbull (Curate) on May 09, 2002 at 02:03 UTC
My favorite way to handle this is with Filter::Handle. For example: use warnings; use strict; use Carp; use Filter::Handle qw/subs/; open (LOGFILE, ">logfile") or die "could not open logfile: $!"; #filter STDERR through an anonymous sub Filter \STDERR, sub {local $_ = "@_"; print LOGFILE "Filtered: $_ "; +$_}; #need a signal handler to capture warnings from carp and warn which ar +e not captured by Filter::Handle (but by capturing ourselves and prin +ting to STDERR, they do get picked up by Filter::Handle) $SIG{__WARN__} = sub {local $_ = "@_"; print STDERR $_}; #prints to both STDERR and to LOGFILE print STDERR "error!\n"; carp "carp!"; warn "warn!"; #STDERR will no longer be filtered through your sub UnFilter \STDERR; print STDERR "not captured to log\n"; warn "this one got away"; close LOGFILE; [download] Update: Added signal handler to capture output of warn and carp	[reply] [d/l]
Re: (RhetTbull) Re: duplicating STDERR to a logfile... by cadphile (Beadle) on May 17, 2002 at 00:50 UTC
Thanks RhetTbull -- This is the exact solution I was hunting for. Simple implementation, and it works just right. cheers Cadphile...	[reply]
Re: duplicating STDERR to a logfile... by jsegal (Friar) on May 08, 2002 at 22:09 UTC
How about (at least on UNIX) `open(STDERR,"\|tee somefile 1>&2"); print STDERR "this goes to STDERR and somefile\n";` [download] (The "1>2" ensures that what gets printed still goes to your main process's STDERR instead of STDOUT). --JAS	[reply] [d/l]
Re: duplicating STDERR to a logfile... by belg4mit (Prior) on May 09, 2002 at 01:42 UTC
Another means would be to install a signal handler, this would receive Carp's cooked messages and you could tee from within. I wouldn't recommend opening the file within the handler though (memory allocaiton and (un)safe signal handling). Alternatively you could just use Carp::longmess and Carp::shortmess yourself. `-- perl -pew "s/\b;([mnst])/'$1/g"`	[reply]


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