Mastering Modern Perl: Writing Efficient and Maintainable Code/

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Exceptions

Exceptions

Learn about exception handling in Perl.

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Good programmers anticipate the unexpected. Files that should exist won’t. A huge disk that should never fill up will. The network that never goes down stops responding. The unbreakable database crashes and eats a table.

The unexpected happens.

Perl handles exceptional conditions through exceptions: a dynamically scoped control flow mechanism designed to raise and handle errors. Robust software must handle them. If we can recover, great! If we can’t, we should log the relevant information and retry.

Throwing exceptions

Suppose we want to write a log file. If we can’t open the file, something has gone wrong. Use die to throw an exception:

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sub open_log_file {
  my $name = shift;
  open my $fh, '>>', $name or die "Can't open log to '$name': $!";
  return $fh;
}
open_log_file('monkeytown.log');

die() sets the global variable $@ to its ...