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autodie

Perl 5 version 18.2 documentation
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autodie

NAME

autodie - Replace functions with ones that succeed or die with lexical scope

SYNOPSIS

  1. use autodie; # Recommended: implies 'use autodie qw(:default)'
  2. use autodie qw(:all); # Recommended more: defaults and system/exec.
  3. use autodie qw(open close); # open/close succeed or die
  4. open(my $fh, "<", $filename); # No need to check!
  5. {
  6. no autodie qw(open); # open failures won't die
  7. open(my $fh, "<", $filename); # Could fail silently!
  8. no autodie; # disable all autodies
  9. }

DESCRIPTION

  1. bIlujDI' yIchegh()Qo'; yIHegh()!
  2. It is better to die() than to return() in failure.
  3. -- Klingon programming proverb.

The autodie pragma provides a convenient way to replace functions that normally return false on failure with equivalents that throw an exception on failure.

The autodie pragma has lexical scope, meaning that functions and subroutines altered with autodie will only change their behaviour until the end of the enclosing block, file, or eval.

If system is specified as an argument to autodie , then it uses IPC::System::Simple to do the heavy lifting. See the description of that module for more information.

EXCEPTIONS

Exceptions produced by the autodie pragma are members of the autodie::exception class. The preferred way to work with these exceptions under Perl 5.10 is as follows:

  1. use feature qw(switch);
  2. eval {
  3. use autodie;
  4. open(my $fh, '<', $some_file);
  5. my @records = <$fh>;
  6. # Do things with @records...
  7. close($fh);
  8. };
  9. given ($@) {
  10. when (undef) { say "No error"; }
  11. when ('open') { say "Error from open"; }
  12. when (':io') { say "Non-open, IO error."; }
  13. when (':all') { say "All other autodie errors." }
  14. default { say "Not an autodie error at all." }
  15. }

Under Perl 5.8, the given/when structure is not available, so the following structure may be used:

  1. eval {
  2. use autodie;
  3. open(my $fh, '<', $some_file);
  4. my @records = <$fh>;
  5. # Do things with @records...
  6. close($fh);
  7. };
  8. if ($@ and $@->isa('autodie::exception')) {
  9. if ($@->matches('open')) { print "Error from open\n"; }
  10. if ($@->matches(':io' )) { print "Non-open, IO error."; }
  11. } elsif ($@) {
  12. # A non-autodie exception.
  13. }

See autodie::exception for further information on interrogating exceptions.

CATEGORIES

Autodie uses a simple set of categories to group together similar built-ins. Requesting a category type (starting with a colon) will enable autodie for all built-ins beneath that category. For example, requesting :file will enable autodie for close, fcntl, fileno, open and sysopen.

The categories are currently:

  1. :all
  2. :default
  3. :io
  4. read
  5. seek
  6. sysread
  7. sysseek
  8. syswrite
  9. :dbm
  10. dbmclose
  11. dbmopen
  12. :file
  13. binmode
  14. close
  15. fcntl
  16. fileno
  17. flock
  18. ioctl
  19. open
  20. sysopen
  21. truncate
  22. :filesys
  23. chdir
  24. closedir
  25. opendir
  26. link
  27. mkdir
  28. readlink
  29. rename
  30. rmdir
  31. symlink
  32. unlink
  33. :ipc
  34. pipe
  35. :msg
  36. msgctl
  37. msgget
  38. msgrcv
  39. msgsnd
  40. :semaphore
  41. semctl
  42. semget
  43. semop
  44. :shm
  45. shmctl
  46. shmget
  47. shmread
  48. :socket
  49. accept
  50. bind
  51. connect
  52. getsockopt
  53. listen
  54. recv
  55. send
  56. setsockopt
  57. shutdown
  58. socketpair
  59. :threads
  60. fork
  61. :system
  62. system
  63. exec

Note that while the above category system is presently a strict hierarchy, this should not be assumed.

A plain use autodie implies use autodie qw(:default) . Note that system and exec are not enabled by default. system requires the optional IPC::System::Simple module to be installed, and enabling system or exec will invalidate their exotic forms. See BUGS below for more details.

The syntax:

  1. use autodie qw(:1.994);

allows the :default list from a particular version to be used. This provides the convenience of using the default methods, but the surety that no behavorial changes will occur if the autodie module is upgraded.

autodie can be enabled for all of Perl's built-ins, including system and exec with:

  1. use autodie qw(:all);

FUNCTION SPECIFIC NOTES

flock

It is not considered an error for flock to return false if it fails due to an EWOULDBLOCK (or equivalent) condition. This means one can still use the common convention of testing the return value of flock when called with the LOCK_NB option:

  1. use autodie;
  2. if ( flock($fh, LOCK_EX | LOCK_NB) ) {
  3. # We have a lock
  4. }

Autodying flock will generate an exception if flock returns false with any other error.

system/exec

The system built-in is considered to have failed in the following circumstances:

  • The command does not start.

  • The command is killed by a signal.

  • The command returns a non-zero exit value (but see below).

On success, the autodying form of system returns the exit value rather than the contents of $? .

Additional allowable exit values can be supplied as an optional first argument to autodying system:

  1. system( [ 0, 1, 2 ], $cmd, @args); # 0,1,2 are good exit values

autodie uses the IPC::System::Simple module to change system. See its documentation for further information.

Applying autodie to system or exec causes the exotic forms system { $cmd } @args or exec { $cmd } @args to be considered a syntax error until the end of the lexical scope. If you really need to use the exotic form, you can call CORE::system or CORE::exec instead, or use no autodie qw(system exec) before calling the exotic form.

GOTCHAS

Functions called in list context are assumed to have failed if they return an empty list, or a list consisting only of a single undef element.

DIAGNOSTICS

  • :void cannot be used with lexical scope

    The :void option is supported in Fatal, but not autodie . To workaround this, autodie may be explicitly disabled until the end of the current block with no autodie . To disable autodie for only a single function (eg, open) use no autodie qw(open) .

    autodie performs no checking of called context to determine whether to throw an exception; the explicitness of error handling with autodie is a deliberate feature.

  • No user hints defined for %s

    You've insisted on hints for user-subroutines, either by pre-pending a ! to the subroutine name itself, or earlier in the list of arguments to autodie . However the subroutine in question does not have any hints available.

See also DIAGNOSTICS in Fatal.

BUGS

"Used only once" warnings can be generated when autodie or Fatal is used with package filehandles (eg, FILE ). Scalar filehandles are strongly recommended instead.

When using autodie or Fatal with user subroutines, the declaration of those subroutines must appear before the first use of Fatal or autodie , or have been exported from a module. Attempting to use Fatal or autodie on other user subroutines will result in a compile-time error.

Due to a bug in Perl, autodie may "lose" any format which has the same name as an autodying built-in or function.

autodie may not work correctly if used inside a file with a name that looks like a string eval, such as eval (3).

autodie and string eval

Due to the current implementation of autodie , unexpected results may be seen when used near or with the string version of eval. None of these bugs exist when using block eval.

Under Perl 5.8 only, autodie does not propagate into string eval statements, although it can be explicitly enabled inside a string eval.

Under Perl 5.10 only, using a string eval when autodie is in effect can cause the autodie behaviour to leak into the surrounding scope. This can be worked around by using a no autodie at the end of the scope to explicitly remove autodie's effects, or by avoiding the use of string eval.

None of these bugs exist when using block eval. The use of autodie with block eval is considered good practice.

REPORTING BUGS

Please report bugs via the CPAN Request Tracker at http://rt.cpan.org/NoAuth/Bugs.html?Dist=autodie.

FEEDBACK

If you find this module useful, please consider rating it on the CPAN Ratings service at http://cpanratings.perl.org/rate?distribution=autodie .

The module author loves to hear how autodie has made your life better (or worse). Feedback can be sent to <pjf@perltraining.com.au>.

AUTHOR

Copyright 2008-2009, Paul Fenwick <pjf@perltraining.com.au>

LICENSE

This module is free software. You may distribute it under the same terms as Perl itself.

SEE ALSO

Fatal, autodie::exception, autodie::hints, IPC::System::Simple

Perl tips, autodie at http://perltraining.com.au/tips/2008-08-20.html

ACKNOWLEDGEMENTS

Mark Reed and Roland Giersig -- Klingon translators.

See the AUTHORS file for full credits. The latest version of this file can be found at http://github.com/pfenwick/autodie/tree/master/AUTHORS .