| autodie(3) | User Contributed Perl Documentation | autodie(3) |
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 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, 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> .
| 2021-08-09 | perl v5.32.1 |