Wrapping Perl “die” and “warn” in a utility subrou

Question

I want to write a small subroutine that can decorate all error messages in a consistent way instead of having to copy it all around my program.

However I want the line numbers to be from where it was called, not from where the die/warn occurred.

In C I would just use a preprocessor macro, but Perl does not have those. What is the best way to implement this?

Answer 1

Use Carp for warnings/errors. You can use __WARN__ and __DIE__ hooks to affect what warn prints to the STDERR stream and how die is thrown. Note that they are quite different.

use warnings;
use strict;
use feature 'say';

use Carp;

$SIG{__WARN__} = \&wrap_warn;

sub wrap_warn {
    print "WARNING: @_";
} 

sub level_2 { 
    say "Print from level_2";
    carp "carp from level_2(@_)"; 
}

sub level_1 {
    level_2(@_);
}

level_1("from main");

prints to STDOUT

Print from level_2
WARNING: carp from level_2(from main) at wrap_warn.pl line 19.
        main::level_2('from main') called at wrap_warn.pl line 15
        main::level_1('from main') called at wrap_warn.pl line 22

If you want this to still go to STDERR then use print STDERR "WARNING: @_";

Make sure to carefully read about %SIG in perlvar and warn, at least.

---

While it seems that you want this to be global, I'd like to mention that local-izing changes like this is generally what one wants, if possible. There's an example in this post, and more out there.

Answer 2

Adding the following will add stack traces to exceptions and warnings:

use Carp::Always;

For the occasional use, use the following to avoid modifying your program:

perl -MCarp::Always script args

or

PERL5OPT=-MCarp::Always script args