autodie(3perl) Perl Programmers Reference Guide autodie(3perl)
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
}
print "Hello World" or die $!; # autodie DOESN'T check print!
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:
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", "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);
FUNCTION SPECIFIC NOTES
print
The autodie pragma does not check calls to "print".
flock
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.
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 { $cmd } @args" to be considered a syntax
error until the end of the lexical scope. If you really need to use the
exotic form, you can call "CORE::system" or "CORE::exec" instead, or use
"no autodie qw(system exec)" before calling the exotic form.
GOTCHAS
Functions called in list context are assumed to have failed if they
return an empty list, or a list consisting only of a single undef
element.
Some builtins (e.g. "chdir" or "truncate") has a call signature that
cannot completely be represented with a Perl prototype. This means that
some valid Perl code will be invalid under autodie. As an example:
chdir(BAREWORD);
Without autodie (and assuming BAREWORD is an open filehandle/dirhandle)
this is a valid call to chdir. But under autodie, "chdir" will behave
like it had the prototype ";$" and thus BAREWORD will be a syntax error
(under "use strict". Without strict, it will interpreted as a
filename).
DIAGNOSTICS
:void cannot be used with lexical scope
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.
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 to "autodie". However the subroutine in question does not
have any hints available.
See also "DIAGNOSTICS" in Fatal.
Tips and Tricks
Importing autodie into another namespace than "caller"
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.
BUGS
"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).
autodie and string eval
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.
REPORTING BUGS
Please report bugs via the GitHub Issue Tracker at
<https://github.com/pjf/autodie/issues>.
FEEDBACK
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>.
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, autodie::hints, 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 <https://github.com/pjf/autodie/tree/master/AUTHORS> .
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