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(: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
}
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.
You can enable autodie
for all of Perl's built-ins, including system
and exec
with:
use autodie qw(:all);
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
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.
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 notautodie
. However you can explicitly disable autodie end the end of the current block withno autodie
. To disable autodie for only a single function (eg, open) use orno autodie qw(open)
. - No user hints defined for %s
-
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.
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 2008-2009, 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 .