How can I redirect output of die function to a file in Perl?

Question

I want to redirect the die messages to a separate file so that I can compare that file later to determine what went wrong.

But this code gives me errors:

$ cat test.pl
use strict;
use warnings;

my $log = "msglog.log";
die $log "DEAD$!";

$ perl test.pl
Missing comma after first argument to die function at test.pl line 5, near ""DEAD$!";"
Execution of test.pl aborted due to compilation errors.
$ 

I do not want to do a 2> from the caller. Is there someway to redirect them from within the script?

Sienese

Answer 1

Perl's die prints to STDERR so you could redirect STDERR to a file.

#!/usr/bin/env perl
# the path above depends on your system

open(STDERR, ">>", "errlog.log");
die "Hello";

Toga

This also redirects warn() messages, warnings, and anything else printed to STDERR. Not only that, if someone has done this properly by redefining the DIE handler, it might not even redirect die() messages. – Adamok

Answer 2

You can install a $SIG{__DIE__} handler to be run just before the "die" runs. The handler will be called with the error message which you can log:

local $SIG{__DIE__} = sub {
    my ($message) = @_;
    # log the message        
};

See $SIG{expr} in perlvar for details.

Juliojulis

Answer 3

The Log::Log4perl module offers more than a few options.

One can choose to output the error message to both STDERR and the logfile.

my $logger = Log::Log4perl->init ( 'log.conf' );
# Configuration file controls what to output, like time, line number, class...

$logger->get_logger ( 'Hello::World' );  # Define which class logger to use

.
.
.

open my $fh, '<', $file
  or $logger->logdie ( "Log the demise: $!" );  # ... and die;

While it requires a little bit more effort in terms of setup, its flexibility unlocks a great deal of potential.

Joselynjoseph