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?

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";

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.

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.