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.
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
, open
and 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.
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.
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
>.
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:
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 { $cmd } @args
to be considered a syntax error until the end of the lexical scope. If you really need to use the exotic form, you can call CORE::system
or CORE::exec
instead, or use no autodie qw(system exec)
before calling the exotic form.
Functions called in list context are assumed to have failed if they return an empty list, or a list consisting only of a single undef element.
Some builtins (e.g. chdir
or truncate
) has a call signature that cannot completely be representated with a Perl prototype. This means that some valid Perl code will be invalid under autodie. As an example:
chdir(BAREWORD);
Without autodie (and assuming BAREWORD is an open filehandle/dirhandle) this is a valid call to chdir. But under autodie, chdir
will behave like it had the prototype ";$" 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)
.
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 GitHub Issue Tracker at https://github.com/pjf/autodie/issues or via the CPAN Request Tracker at https://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 https://github.com/pjf/autodie/tree/master/AUTHORS .