How to use die to throw exceptions in Perl?

In Perl, die is the standard way to throw exceptions or fatal errors. It immediately terminates the program (or the current eval block), printing an error message to STDERR and appending the script name and line number unless the message ends with a newline.

How die Works

You can pass die any string message describing the error. It behaves like this:

• Prints the error message to STDERR
• Appends file and line information unless you end with a newline
• Exits the program with a non-zero status (almost always 255)

Using die with eval for Exception Handling

Perl does not have built-in exception objects, but you can simulate try-catch behavior with eval. If die is called inside an eval, Perl sets the special variable $@ to the error string instead of exiting, allowing your script to handle the error gracefully.

Common Gotchas

• If your die message ends with a newline (\n), Perl will not append file/line info.
• Inside eval, die stops only the eval block, not the entire program.
• The exit code on an untrapped die is 255 by default.

Version Notes

die has been consistent since Perl 5. For more structured exception handling, newer Perl versions encourage modules like Try::Tiny, but plain die and eval remain effective and core to Perl programming.

Example: Using die with eval to Catch Errors

use strict;
use warnings;

sub divide {
    my ($numerator, $denominator) = @_;
    
    # Throw exception if denominator is zero
    die "Division by zero error" unless $denominator;
    
    return $numerator / $denominator;
}

my $x = 10;
my $y = 0;

my $result = eval {
    divide($x, $y);
};

if ($@) {
    print "Caught exception: $@";
} else {
    print "Division result: $result\n";
}

This example defines a divide subroutine that dies on zero denominator. The surrounding eval traps the die, setting $@ to the error message instead of exiting the program, allowing graceful error handling.

Summary

• die throws fatal exceptions in Perl by printing an error and exiting immediately.
• Wrap vulnerable code in eval to catch errors thrown by die and handle them safely.
• Avoid ending your error messages with newlines if you want file and line info appended.
• This approach enables simple, effective exception handling without external modules.