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 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 } print "Hello World" or die $!; # autodie DOESN'T check print!
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.
autodie
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.
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.
system
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:
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.
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, open and sysopen.
:file
close
fcntl
open
sysopen
The categories are currently:
:all :default :io read seek sysread sysseek syswrite :dbm dbmclose dbmopen :file binmode close chmod chown fcntl flock ioctl open sysopen truncate :filesys chdir closedir opendir link mkdir readlink rename rmdir symlink unlink :ipc kill 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.
use autodie
use autodie qw(:default)
exec
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 behavioral changes will occur if the autodie module is upgraded.
:default
autodie can be enabled for all of Perl's built-ins, including system and exec with:
use autodie qw(:all);
The autodie pragma does not check calls to print.
print
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:
flock
EWOULDBLOCK
LOCK_NB
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.
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:
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.
system { $cmd } @args
exec { $cmd } @args
CORE::system
CORE::exec
no autodie qw(system exec)
Functions called in list context are assumed to have failed if they return an empty list, or a list consisting only of a single undef element.
Some builtins (e.g. chdir or truncate) has a call signature that cannot completely be represented with a Perl prototype. This means that some valid Perl code will be invalid under autodie. As an example:
chdir
truncate
chdir(BAREWORD);
Without autodie (and assuming BAREWORD is an open filehandle/dirhandle) this is a valid call to chdir. But under autodie, chdir will behave like it had the prototype ";$" and thus BAREWORD will be a syntax error (under "use strict". Without strict, it will interpreted as a filename).
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).
:void
no autodie
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.
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.
It is possible to import autodie into a different namespace by using Import::Into. However, you have to pass a "caller depth" (rather than a package name) for this to work correctly.
"Used only once" warnings can be generated when autodie or Fatal is used with package filehandles (eg, FILE). Scalar filehandles are strongly recommended instead.
Fatal
FILE
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).
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.
Please report bugs via the GitHub Issue Tracker at https://github.com/pjf/autodie/issues.
If you find this module useful, please consider rating it on metacpan at https://metacpan.org/pod/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>.
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 at http://perltraining.com.au/tips/2008-08-20.html
Mark Reed and Roland Giersig -- Klingon translators.
See the AUTHORS file for full credits. The latest version of this file can be found at https://github.com/pjf/autodie/tree/master/AUTHORS .
To install autodie, copy and paste the appropriate command in to your terminal.
cpanm
cpanm autodie
CPAN shell
perl -MCPAN -e shell install autodie
For more information on module installation, please visit the detailed CPAN module installation guide.