autodie(3p) Perl Programmers Reference Guide autodie(3p) #
autodie(3p) Perl Programmers Reference Guide autodie(3p)
NNAAMMEE #
autodie - Replace functions with ones that succeed or die with lexical
scope
SSYYNNOOPPSSIISS #
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!
DDEESSCCRRIIPPTTIIOONN #
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 _l_e_x_i_c_a_l _s_c_o_p_e, 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.
EEXXCCEEPPTTIIOONNSS #
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.
CCAATTEEGGOORRIIEESS #
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);
FFUUNNCCTTIIOONN SSPPEECCIIFFIICC NNOOTTEESS #
pprriinntt The autodie pragma ddooeess nnoott cchheecckk ccaallllss ttoo “"pprriinntt"”.
fflloocckk 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.
ssyysstteemm//eexxeecc 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 _e_x_i_t _v_a_l_u_e 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 { $cmd } @args" to be considered a syntax error
until the end of the lexical scope. If you really need to use the exotic
form, you can call "CORE::system" or "CORE::exec" instead, or use "no
autodie qw(system exec)" before calling the exotic form.
GGOOTTCCHHAASS #
Functions called in list context are assumed to have failed if they
return an empty list, or a list consisting only of a single undef
element.
Some builtins (e.g. "chdir" or "truncate") has a call signature that
cannot completely be represented with a Perl prototype. This means that
some valid Perl code will be invalid under autodie. As an example:
chdir(BAREWORD);
Without autodie (and assuming BAREWORD is an open filehandle/dirhandle)
this is a valid call to chdir. But under autodie, "chdir" will behave
like it had the prototype ";$" and thus BAREWORD will be a syntax error
(under "use strict". Without strict, it will interpreted as a filename).
DDIIAAGGNNOOSSTTIICCSS #
: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.
TTiippss aanndd TTrriicckkss IImmppoorrttiinngg aauuttooddiiee iinnttoo aannootthheerr nnaammeessppaaccee tthhaann “"ccaalllleerr"” 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.
BBUUGGSS #
"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 _e_v_a_l _(_3_).
aauuttooddiiee aanndd ssttrriinngg eevvaall Due to the current implementation of “autodie”, unexpected results may be seen when used near or with the string version of eval. _N_o_n_e _o_f _t_h_e_s_e _b_u_g_s _e_x_i_s_t _w_h_e_n _u_s_i_n_g _b_l_o_c_k _e_v_a_l.
Under Perl 5.8 only, "autodie" _d_o_e_s _n_o_t 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.
_N_o_n_e _o_f _t_h_e_s_e _b_u_g_s _e_x_i_s_t _w_h_e_n _u_s_i_n_g _b_l_o_c_k _e_v_a_l. The use of "autodie"
with block eval is considered good practice.
RREEPPOORRTTIINNGG BBUUGGSS #
Please report bugs via the GitHub Issue Tracker at
<https://github.com/pjf/autodie/issues>.
FFEEEEDDBBAACCKK #
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>.
AAUUTTHHOORR #
Copyright 2008-2009, Paul Fenwick <pjf@perltraining.com.au>
LLIICCEENNSSEE #
This module is free software. You may distribute it under the same terms
as Perl itself.
SSEEEE AALLSSOO #
Fatal, autodie::exception, autodie::hints, IPC::System::Simple
_P_e_r_l _t_i_p_s_, _a_u_t_o_d_i_e at <http://perltraining.com.au/tips/2008-08-20.html>
AACCKKNNOOWWLLEEDDGGEEMMEENNTTSS #
Mark Reed and Roland Giersig -- Klingon translators.
See the _A_U_T_H_O_R_S file for full credits. The latest version of this file
can be found at <https://github.com/pjf/autodie/tree/master/AUTHORS> .
perl v5.36.3 2023-02-15 autodie(3p)