How do I output error messages to a file?

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

O Wise Monks, I'm using Active State on WinXP, where this little script causes an error, outputted to my msDos command window.

#errorToOut.pl
use strict;
use warnings;

#causes error.
print $forgotToDeclareThis
[download]

I'd like to capture all errors to a text file to review later. This is for situation I'm having in another program, where I get so many error messages so fast that they scroll of the command line before I can type ctrl-c, so I can't get back to the first error, which is probably the root of all the later evil.

I tried perl errorToOut.pl > output.txt but this simpleminded little attempt of mine didn't work.

Wise monks, can someone help me with this?

Comment on How do I output error messages to a file? Select or Download Code

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Re: How do I output error messages to a file? by gellyfish (Monsignor) on Jan 26, 2005 at 11:14 UTC
I think that `2>output.txt` will work on XP. /J\	[reply] [d/l]
Re^2: How do I output error messages to a file? by inman (Curate) on Jan 26, 2005 at 11:57 UTC
The OP will want to ammend their code to print the errors to STDERR so that they can be redirected with `>2 output.txt`. Normal output is still printed to STDOUT (usually the console). E.g. `print STDERR "This didn't work as expected!\n";` [download]	[reply] [d/l] [select]
Re^3: How do I output error messages to a file? by gellyfish (Monsignor) on Jan 26, 2005 at 12:21 UTC
I think the OP was talking about warnings and/or `strict` errors, which already do go to STDERR but yes if they want to catch their own messages then these will have to be either explicitly printed to STDERR or output with `warn`. /J\	[reply] [d/l] [select]
Re: How do I output error messages to a file? by jweed (Chaplain) on Jan 26, 2005 at 11:26 UTC
Redirect STDERR from within the program: `open STDERR, ">", "/path/to/log";` [download] Code is (almost) always untested. http://www.justicepoetic.net/	[reply] [d/l]
Re: How do I output error messages to a file? by Frantz (Monk) on Jan 26, 2005 at 11:41 UTC
You can try File::Log with 'stderrRedirect => 1' when you buid your object See File::Log	[reply]
Re: How do I output error messages to a file? by tphyahoo (Vicar) on Jan 26, 2005 at 12:25 UTC
Thanks. My vote for the best solution is the first one. `perl errorToOut.pl 2> output.txt` [download] Simple, a bit cryptic, but it works.	[reply] [d/l]
Re^2: How do I output error messages to a file? by renz (Scribe) on Jan 26, 2005 at 14:59 UTC
2>file is a pretty standard way to redirect errors. Unix has been doing it since the dawn of time. -- /renz. "I often wonder if I really need all of these bones." --Sean Stolon.	[reply]
Re^2: How do I output error messages to a file? by tphyahoo (Vicar) on Jan 27, 2005 at 09:40 UTC
On second thought, I am beginning to see the beauty of `open STDERR, ">", "/path/to/log";` [download] which I will be coupling this with `open STDOUT, ">", "path/to/log";` [download] I debug more with print statements than with the perl debugger, so this allows me to see my debugging statements along with the more serious perl complaints to see where my code is acting up. Thanks again to everyone who enlightened me. UPDATE: Here's a simple demonstration that may be helpful to newbies. `#errorToOut.pl use strict; use warnings; open STDERR, ">>", "log.txt"; open STDOUT, ">>", "log.txt"; #outputted to stderr warn "warning!"; #outputted to stdout print "Test."; #Log.txt winds up looking like: #warning! at errorToOut.pl line 9. #Test.` [download]	[reply] [d/l] [select]
Re: How do I output error messages to a file? by ambrus (Abbot) on Jan 26, 2005 at 14:57 UTC
Reopening STDERR is right, but there is an other solution too, using `$SIG{__DIE__}` as follows (untested code): `BEGIN{ open LOGFILE, ">>", "/path/to/log" or die "cannot open logfile: $!"; $SIG{__DIE__}= sub { print LOGFILE $_[0]; } $SIG{__WARN__}= sub { print LOGFILE $_[0]; } }` [download]	[reply] [d/l] [select]