#!/usr/bin/env perl

use Exception::Class ( 'MyException' );

# try
my $z = 0;

eval {
  eval { my $result = ( 23 / $z ) }
    || MyException->throw( error => 'I feel funny.' )
};

# my $e;
# catch
if( my $e = Exception::Class->caught( 'MyException' ) ) {
  warn $e->error, "\n", $e->trace->as_string, "\n";
  warn join ' ', $e->euid, $e->egid, $e->uid, $e->gid, $e->pid, $e->ti
+me;
  exit;
} else {
  $e = Exception::Class->caught();
  ref $e ? $e->rethrow : die $e;
}
__END__

I feel funny.
Trace begun at index.pl line 9
eval {...} at index.pl line 8

1000 1000 1000 121 120 117 115 109 108 106 104 46 44 30 29 25 24 20 6 
+4 0 1000 1000 1000 121 120 117 115 109 108 106 104 46 44 30 29 25 24 
+20 6 4 0 10107 1221493762 at index.pl line 17.
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dear massa, thanks for your help. Would you mind to give a quick explanation of the effect of this eval wrapper around the division by zero expression?

The important bit is that you are eval-ing the '27/0', but the "|| throw exception" part is outside the eval. So when the eval dies out of the execution and returns false, the exception is thrown.

The structure is eval {"risky expression"} or throw exception.
NOT eval {"risky expression; or throw exception"}

It should be noted that the return value of eval is:

"...the value of the last expression evaluated inside the mini-program; a return statement may be also used, just as with subroutines."

So, you should add a "1;" or "return 1;" to the end, otherwise you would throw some spurious exceptions if the answer is supposed to be zero (such as 5*2-10)