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autodie.3pm

NAME

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

SYNOPSIS

     use autodie;    # Recommended, implies 'use autodie qw(:default)'
 
     use autodie qw(open close);   # open/close succeed or die
 
     open(my $fh, "<", $filename); # No need to check!
 
     {
         no autodie qw(open);          # open failures won't die
         open(my $fh, "<", $filename); # Could fail silently!
         no autodie;                   # disable all autodies
     }
 
 

DESCRIPTION

         bIlujDI' yIchegh()Qo'; yIHegh()!
 
         It is better to die() than to return() in failure.
 
                 -- 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:

     use feature qw(switch);
 
     eval {
         use autodie;
 
         open(my $fh, '<', $some_file);
 
         my @records = <$fh>;
 
         # Do things with @records...
 
         close($fh);
 
     };
 
     given ($@) {
         when (undef)   { say "No error";                    }
         when ('open')  { say "Error from open";             }
         when (':io')   { say "Non-open, IO error.";         }
         when (':all')  { say "All other autodie errors."    }
         default        { say "Not an autodie error at all." }
     }
 
 

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

     eval {
         use autodie;
 
         open(my $fh, '<', $some_file);
 
         my @records = <$fh>;
 
         # Do things with @records...
 
         close($fh);
     };
 
     if ($@ and $@->isa('autodie::exception')) {
         if ($@->matches('open')) { print "Error from open\n";   }
         if ($@->matches(':io' )) { print "Non-open, IO error."; }
     } elsif ($@) {
         # A non-autodie exception.
     }
 
 

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:

     :all
         :default
             :io
                 read
                 seek
                 sysread
                 sysseek
                 syswrite
                 :dbm
                     dbmclose
                     dbmopen
                 :file
                     binmode
                     close
                     fcntl
                     fileno
                     flock
                     ioctl
                     open
                     sysopen
                     truncate
                 :filesys
                     chdir
                     closedir
                     opendir
                     link
                     mkdir
                     readlink
                     rename
                     rmdir
                     symlink
                     unlink
                 :ipc
                     pipe
                     :msg
                         msgctl
                         msgget
                         msgrcv
                         msgsnd
                     :semaphore
                         semctl
                         semget
                         semop
                     :shm
                         shmctl
                         shmget
                         shmread
                 :socket
                     accept
                     bind
                     connect
                     getsockopt
                     listen
                     recv
                     send
                     setsockopt
                     shutdown
                     socketpair
             :threads
                 fork
         :system
             system
             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:

     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 surity that no behavorial changes will occur if the "autodie" module is upgraded.

FUNCTION SPECIFIC NOTES

flock

It is not considered an error for "flock" to return false if it fails 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:

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

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

system/exec

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". However you can explicitly disable autodie end the end of the current block with "no autodie". To disable autodie for only a single function (eg, open) use or "no autodie qw(open)".

See also ``DIAGNOSTICS'' in Fatal.

BUGS

``Used only once'' warnings can be generated when "autodie" or "Fatal" is used with package filehandles (eg, "FILE"). It's strongly recommended you use scalar filehandles instead.

Under Perl 5.8 only, "autodie" does not propagate into string "eval" statements, although it can be explicitly enabled inside a string "eval". This bug does not affect block "eval" statements in any version of Perl.

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 ue "Fatal" or "autodie" on other user subroutines will result in a compile-time error.

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, 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, 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/AUTHORS> .