Catching STDERR

[kiseok7]

How can I write STDERR to file in perl.

like this :

print STDERR "script start\n";

do_something or die "error in something";

print STDERR "script end\n";

I would like to write "error in something" on file(error.log)

[mr.nick]

Simple. Just open a file with the filehandle of STDERR:

#!/usr/bin/perl

use strict;

open(STDERR,">>error.log") || die "Couldn't redirect STDERR: $!\n";
print STDERR "This goes to the file.\n";
warn "As does this.";
die "And this does, too!\n";
close STDERR;

Update: If you want to restore the original filehandle, then you'll have to do something like this:

open(OLDERR,">&STDERR") || die "Couldn't dup STDERR: $!\n";
open(STDERR,">>error.log") || die "Couldn't redirect STDERR: $!\n";
print STDERR "This goes to the file.\n";
warn "As does this.";
open(STDERR,">&OLDERR") || die "Couldn't restore STDERR: $!\n";
warn "This goes to the screen.";

Btw, this is almost entirely taken from perldoc -f open.

mr.nick ...

[kiseok7]

[RhetTbull]

The aforementioned methods will work great if you want to redirect STDERR to a file. However, if you want to redirect it to a file AND still display it on the STDERR device (e.g. the screen) you might try Filter::Handle. It will let you attach a sub to a file handle (including STDERR) so that you can print the output to a file or filter it any way you like in addition to printing to the terminal. Here's a little snippet to get you started.

use warnings;
use strict;
use Filter::Handle qw/subs/;

open (LOGFILE, ">logfile") || die "could not open logfile";

#filter STDERR through an anonymous sub
Filter \*STDERR, sub {local $_ = "@_"; print LOGFILE "Filtered: $_ "; 
+$_};

#prints to both STDERR and to LOGFILE
print STDERR "error!\n";

#STDERR will no longer be filtered through your sub
UnFilter \*STDERR;

close LOGFILE;

Regards,
Rhet

[Ovid]

I can't guarantee the robustness of this solution, but trying opening STDERR for writing:

use strict;
use warnings;

open STDERR, "> somefile.txt" or die $!; 
die "We're dead!";

This works for me, but no guarantees as I've never tried to redirect STDERR.

Cheers,
Ovid

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[tye]

Just a little FYI: Ovid's doubts are unfounded as this is the most reliable way of catching STDERR. I clicked to this thread fearing I'd see lots of advice to use $SIG{__DIE__}, eval, CORE::GLOBAL::die, tie, pipe-and-fork... A simple open is much preferred. (:

        - tye (but my friends call me "Tye")