autodie - Replace functions with ones that succeed or die with lexical scope
use autodie; # Recommended: implies 'use autodie qw(:default)'use autodie qw(:all); # Recommended more: defaults and system/exec.use autodie qw(open close); # open/close succeed or dieopen(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}bIlujDI' yIchegh()Qo'; yIHegh()!It is better to die() than to return() in failure. -- Klingon programming proverb.Theautodie pragma provides a convenient way to replace functions that normally return false on failure with equivalents that throw an exception on failure.
Theautodie pragma haslexical scope, meaning that functions and subroutines altered withautodie will only change their behaviour until the end of the enclosing block, file, oreval.
Ifsystem is specified as an argument toautodie, then it usesIPC::System::Simple to do the heavy lifting. See the description of that module for more information.
Exceptions produced by theautodie pragma are members of theautodie::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, thegiven/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.}Seeautodie::exception for further information on interrogating exceptions.
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 forclose,fcntl,fileno,open andsysopen.
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 execNote that while the above category system is presently a strict hierarchy, this should not be assumed.
A plainuse autodie impliesuse autodie qw(:default). Note thatsystem andexec are not enabled by default.system requires the optionalIPC::System::Simple module to be installed, and enablingsystem orexec 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 surety that no behavorial changes will occur if theautodie module is upgraded.
autodie can be enabled for all of Perl's built-ins, includingsystem andexec with:
use autodie qw(:all);It is not considered an error forflock to return false if it fails due to anEWOULDBLOCK (or equivalent) condition. This means one can still use the common convention of testing the return value offlock when called with theLOCK_NB option:
use autodie;if ( flock($fh, LOCK_EX | LOCK_NB) ) { # We have a lock}Autodyingflock will generate an exception ifflock returns false with any other error.
Thesystem built-in is considered to have failed in the following circumstances:
The command does not start.
The command is killed by a signal.
The command returns a non-zero exit value (but see below).
On success, the autodying form ofsystem returns theexit value rather than the contents of$?.
Additional allowable exit values can be supplied as an optional first argument to autodyingsystem:
system( [ 0, 1, 2 ], $cmd, @args); # 0,1,2 are good exit valuesautodie uses theIPC::System::Simple module to changesystem. See its documentation for further information.
Applyingautodie tosystem orexec causes the exotic formssystem { $cmd } @args orexec { $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 callCORE::system orCORE::exec instead, or useno autodie qw(system exec) before calling the exotic form.
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.
The:void option is supported inFatal, but notautodie. To workaround this,autodie may be explicitly disabled until the end of the current block withno autodie. To disable autodie for only a single function (eg, open) useno autodie qw(open).
autodie performs no checking of called context to determine whether to throw an exception; the explicitness of error handling withautodie is a deliberate feature.
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 toautodie. However the subroutine in question does not have any hints available.
See also"DIAGNOSTICS" in Fatal.
"Used only once" warnings can be generated whenautodie orFatal is used with package filehandles (eg,FILE). Scalar filehandles are strongly recommended instead.
When usingautodie orFatal with user subroutines, the declaration of those subroutines must appear before the first use ofFatal orautodie, or have been exported from a module. Attempting to useFatal orautodie 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 aseval (3).
Due to the current implementation ofautodie, 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,autodiedoes not propagate into stringeval statements, although it can be explicitly enabled inside a stringeval.
Under Perl 5.10 only, using a string eval whenautodie is in effect can cause the autodie behaviour to leak into the surrounding scope. This can be worked around by using ano 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 ofautodie with block eval is considered good practice.
Please report bugs via the CPAN Request Tracker athttp://rt.cpan.org/NoAuth/Bugs.html?Dist=autodie.
If you find this module useful, please consider rating it on the CPAN Ratings service athttp://cpanratings.perl.org/rate?distribution=autodie .
The module author loves to hear howautodie has made your life better (or worse). Feedback can be sent to <pjf@perltraining.com.au>.
Copyright 2008-2009, Paul Fenwick <pjf@perltraining.com.au>
This module is free software. You may distribute it under the same terms as Perl itself.
Fatal,autodie::exception,autodie::hints,IPC::System::Simple
Perl tips, autodie athttp://perltraining.com.au/tips/2008-08-20.html
Mark Reed and Roland Giersig -- Klingon translators.
See theAUTHORS file for full credits. The latest version of this file can be found athttp://github.com/pfenwick/autodie/tree/master/AUTHORS .
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