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
- }
- 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 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.
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 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:
- use autodie qw(:all);
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:
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.
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 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.
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.
"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).
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 CPAN Request Tracker at http://rt.cpan.org/NoAuth/Bugs.html?Dist=autodie.
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>.
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 http://github.com/pfenwick/autodie/tree/master/AUTHORS .