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.\" ========================================================================
.\"
.IX Title "autodie 3"
.TH autodie 3 "2019-10-24" "perl v5.30.2" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
autodie \- Replace functions with ones that succeed or die with lexical scope
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& use autodie; # Recommended: implies \*(Aquse autodie qw(:default)\*(Aq
\&
\& 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\*(Aqt die
\& open(my $fh, "<", $filename); # Could fail silently!
\& no autodie; # disable all autodies
\& }
\&
\& print "Hello World" or die $!; # autodie DOESN\*(AqT check print!
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
.Vb 1
\& bIlujDI\*(Aq yIchegh()Qo\*(Aq; yIHegh()!
\&
\& It is better to die() than to return() in failure.
\&
\& \-\- Klingon programming proverb.
.Ve
.PP
The \f(CW\*(C`autodie\*(C'\fR pragma provides a convenient way to replace functions
that normally return false on failure with equivalents that throw
an exception on failure.
.PP
The \f(CW\*(C`autodie\*(C'\fR pragma has \fIlexical scope\fR, meaning that functions
and subroutines altered with \f(CW\*(C`autodie\*(C'\fR will only change their behaviour
until the end of the enclosing block, file, or \f(CW\*(C`eval\*(C'\fR.
.PP
If \f(CW\*(C`system\*(C'\fR is specified as an argument to \f(CW\*(C`autodie\*(C'\fR, then it
uses IPC::System::Simple to do the heavy lifting. See the
description of that module for more information.
.SH "EXCEPTIONS"
.IX Header "EXCEPTIONS"
Exceptions produced by the \f(CW\*(C`autodie\*(C'\fR pragma are members of the
autodie::exception class. The preferred way to work with
these exceptions under Perl 5.10 is as follows:
.PP
.Vb 1
\& use feature qw(switch);
\&
\& eval {
\& use autodie;
\&
\& open(my $fh, \*(Aq<\*(Aq, $some_file);
\&
\& my @records = <$fh>;
\&
\& # Do things with @records...
\&
\& close($fh);
\&
\& };
\&
\& given ($@) {
\& when (undef) { say "No error"; }
\& when (\*(Aqopen\*(Aq) { say "Error from open"; }
\& when (\*(Aq:io\*(Aq) { say "Non\-open, IO error."; }
\& when (\*(Aq:all\*(Aq) { say "All other autodie errors." }
\& default { say "Not an autodie error at all." }
\& }
.Ve
.PP
Under Perl 5.8, the \f(CW\*(C`given/when\*(C'\fR structure is not available, so the
following structure may be used:
.PP
.Vb 2
\& eval {
\& use autodie;
\&
\& open(my $fh, \*(Aq<\*(Aq, $some_file);
\&
\& my @records = <$fh>;
\&
\& # Do things with @records...
\&
\& close($fh);
\& };
\&
\& if ($@ and $@\->isa(\*(Aqautodie::exception\*(Aq)) {
\& if ($@\->matches(\*(Aqopen\*(Aq)) { print "Error from open\en"; }
\& if ($@\->matches(\*(Aq:io\*(Aq )) { print "Non\-open, IO error."; }
\& } elsif ($@) {
\& # A non\-autodie exception.
\& }
.Ve
.PP
See autodie::exception for further information on interrogating
exceptions.
.SH "CATEGORIES"
.IX Header "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 \f(CW\*(C`:file\*(C'\fR will enable autodie for \f(CW\*(C`close\*(C'\fR, \f(CW\*(C`fcntl\*(C'\fR,
\&\f(CW\*(C`open\*(C'\fR and \f(CW\*(C`sysopen\*(C'\fR.
.PP
The categories are currently:
.PP
.Vb 10
\& :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
.Ve
.PP
Note that while the above category system is presently a strict
hierarchy, this should not be assumed.
.PP
A plain \f(CW\*(C`use autodie\*(C'\fR implies \f(CW\*(C`use autodie qw(:default)\*(C'\fR. Note that
\&\f(CW\*(C`system\*(C'\fR and \f(CW\*(C`exec\*(C'\fR are not enabled by default. \f(CW\*(C`system\*(C'\fR requires
the optional IPC::System::Simple module to be installed, and enabling
\&\f(CW\*(C`system\*(C'\fR or \f(CW\*(C`exec\*(C'\fR will invalidate their exotic forms. See \*(L"\s-1BUGS\*(R"\s0
below for more details.
.PP
The syntax:
.PP
.Vb 1
\& use autodie qw(:1.994);
.Ve
.PP
allows the \f(CW\*(C`:default\*(C'\fR 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 \f(CW\*(C`autodie\*(C'\fR module is
upgraded.
.PP
\&\f(CW\*(C`autodie\*(C'\fR can be enabled for all of Perl's built-ins, including
\&\f(CW\*(C`system\*(C'\fR and \f(CW\*(C`exec\*(C'\fR with:
.PP
.Vb 1
\& use autodie qw(:all);
.Ve
.SH "FUNCTION SPECIFIC NOTES"
.IX Header "FUNCTION SPECIFIC NOTES"
.SS "print"
.IX Subsection "print"
The autodie pragma \fB<does not check calls to \f(CB\*(C`print\*(C'\fB\fR>.
.SS "flock"
.IX Subsection "flock"
It is not considered an error for \f(CW\*(C`flock\*(C'\fR to return false if it fails
due to an \f(CW\*(C`EWOULDBLOCK\*(C'\fR (or equivalent) condition. This means one can
still use the common convention of testing the return value of
\&\f(CW\*(C`flock\*(C'\fR when called with the \f(CW\*(C`LOCK_NB\*(C'\fR option:
.PP
.Vb 1
\& use autodie;
\&
\& if ( flock($fh, LOCK_EX | LOCK_NB) ) {
\& # We have a lock
\& }
.Ve
.PP
Autodying \f(CW\*(C`flock\*(C'\fR will generate an exception if \f(CW\*(C`flock\*(C'\fR returns
false with any other error.
.SS "system/exec"
.IX Subsection "system/exec"
The \f(CW\*(C`system\*(C'\fR built-in is considered to have failed in the following
circumstances:
.IP "\(bu" 4
The command does not start.
.IP "\(bu" 4
The command is killed by a signal.
.IP "\(bu" 4
The command returns a non-zero exit value (but see below).
.PP
On success, the autodying form of \f(CW\*(C`system\*(C'\fR returns the \fIexit value\fR
rather than the contents of \f(CW$?\fR.
.PP
Additional allowable exit values can be supplied as an optional first
argument to autodying \f(CW\*(C`system\*(C'\fR:
.PP
.Vb 1
\& system( [ 0, 1, 2 ], $cmd, @args); # 0,1,2 are good exit values
.Ve
.PP
\&\f(CW\*(C`autodie\*(C'\fR uses the IPC::System::Simple module to change \f(CW\*(C`system\*(C'\fR.
See its documentation for further information.
.PP
Applying \f(CW\*(C`autodie\*(C'\fR to \f(CW\*(C`system\*(C'\fR or \f(CW\*(C`exec\*(C'\fR causes the exotic
forms \f(CW\*(C`system { $cmd } @args \*(C'\fR or \f(CW\*(C`exec { $cmd } @args\*(C'\fR
to be considered a syntax error until the end of the lexical scope.
If you really need to use the exotic form, you can call \f(CW\*(C`CORE::system\*(C'\fR
or \f(CW\*(C`CORE::exec\*(C'\fR instead, or use \f(CW\*(C`no autodie qw(system exec)\*(C'\fR before
calling the exotic form.
.SH "GOTCHAS"
.IX Header "GOTCHAS"
Functions called in list context are assumed to have failed if they
return an empty list, or a list consisting only of a single undef
element.
.PP
Some builtins (e.g. \f(CW\*(C`chdir\*(C'\fR or \f(CW\*(C`truncate\*(C'\fR) has a call signature that
cannot completely be representated with a Perl prototype. This means
that some valid Perl code will be invalid under autodie. As an example:
.PP
.Vb 1
\& chdir(BAREWORD);
.Ve
.PP
Without autodie (and assuming \s-1BAREWORD\s0 is an open
filehandle/dirhandle) this is a valid call to chdir. But under
autodie, \f(CW\*(C`chdir\*(C'\fR will behave like it had the prototype \*(L";$\*(R" and thus
\&\s-1BAREWORD\s0 will be a syntax error (under \*(L"use strict\*(R". Without strict, it
will interpreted as a filename).
.SH "DIAGNOSTICS"
.IX Header "DIAGNOSTICS"
.IP ":void cannot be used with lexical scope" 4
.IX Item ":void cannot be used with lexical scope"
The \f(CW\*(C`:void\*(C'\fR option is supported in Fatal, but not
\&\f(CW\*(C`autodie\*(C'\fR. To workaround this, \f(CW\*(C`autodie\*(C'\fR may be explicitly disabled until
the end of the current block with \f(CW\*(C`no autodie\*(C'\fR.
To disable autodie for only a single function (eg, open)
use \f(CW\*(C`no autodie qw(open)\*(C'\fR.
.Sp
\&\f(CW\*(C`autodie\*(C'\fR performs no checking of called context to determine whether to throw
an exception; the explicitness of error handling with \f(CW\*(C`autodie\*(C'\fR is a deliberate
feature.
.ie n .IP "No user hints defined for %s" 4
.el .IP "No user hints defined for \f(CW%s\fR" 4
.IX Item "No user hints defined for %s"
You've insisted on hints for user-subroutines, either by pre-pending
a \f(CW\*(C`!\*(C'\fR to the subroutine name itself, or earlier in the list of arguments
to \f(CW\*(C`autodie\*(C'\fR. However the subroutine in question does not have
any hints available.
.PP
See also \*(L"\s-1DIAGNOSTICS\*(R"\s0 in Fatal.
.SH "BUGS"
.IX Header "BUGS"
\&\*(L"Used only once\*(R" warnings can be generated when \f(CW\*(C`autodie\*(C'\fR or \f(CW\*(C`Fatal\*(C'\fR
is used with package filehandles (eg, \f(CW\*(C`FILE\*(C'\fR). Scalar filehandles are
strongly recommended instead.
.PP
When using \f(CW\*(C`autodie\*(C'\fR or \f(CW\*(C`Fatal\*(C'\fR with user subroutines, the
declaration of those subroutines must appear before the first use of
\&\f(CW\*(C`Fatal\*(C'\fR or \f(CW\*(C`autodie\*(C'\fR, or have been exported from a module.
Attempting to use \f(CW\*(C`Fatal\*(C'\fR or \f(CW\*(C`autodie\*(C'\fR on other user subroutines will
result in a compile-time error.
.PP
Due to a bug in Perl, \f(CW\*(C`autodie\*(C'\fR may \*(L"lose\*(R" any format which has the
same name as an autodying built-in or function.
.PP
\&\f(CW\*(C`autodie\*(C'\fR may not work correctly if used inside a file with a
name that looks like a string eval, such as \fIeval (3)\fR.
.SS "autodie and string eval"
.IX Subsection "autodie and string eval"
Due to the current implementation of \f(CW\*(C`autodie\*(C'\fR, unexpected results
may be seen when used near or with the string version of eval.
\&\fINone of these bugs exist when using block eval\fR.
.PP
Under Perl 5.8 only, \f(CW\*(C`autodie\*(C'\fR \fIdoes not\fR propagate into string \f(CW\*(C`eval\*(C'\fR
statements, although it can be explicitly enabled inside a string
\&\f(CW\*(C`eval\*(C'\fR.
.PP
Under Perl 5.10 only, using a string eval when \f(CW\*(C`autodie\*(C'\fR is in
effect can cause the autodie behaviour to leak into the surrounding
scope. This can be worked around by using a \f(CW\*(C`no autodie\*(C'\fR at the
end of the scope to explicitly remove autodie's effects, or by
avoiding the use of string eval.
.PP
\&\fINone of these bugs exist when using block eval\fR. The use of
\&\f(CW\*(C`autodie\*(C'\fR with block eval is considered good practice.
.SS "\s-1REPORTING BUGS\s0"
.IX Subsection "REPORTING BUGS"
Please report bugs via the GitHub Issue Tracker at
<https://github.com/pjf/autodie/issues> or via the \s-1CPAN\s0 Request
Tracker at <https://rt.cpan.org/NoAuth/Bugs.html?Dist=autodie>.
.SH "FEEDBACK"
.IX Header "FEEDBACK"
If you find this module useful, please consider rating it on the
\&\s-1CPAN\s0 Ratings service at
<http://cpanratings.perl.org/rate?distribution=autodie> .
.PP
The module author loves to hear how \f(CW\*(C`autodie\*(C'\fR has made your life
better (or worse). Feedback can be sent to
<pjf@perltraining.com.au>.
.SH "AUTHOR"
.IX Header "AUTHOR"
Copyright 2008\-2009, Paul Fenwick <pjf@perltraining.com.au>
.SH "LICENSE"
.IX Header "LICENSE"
This module is free software. You may distribute it under the
same terms as Perl itself.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Fatal, autodie::exception, autodie::hints, IPC::System::Simple
.PP
\&\fIPerl tips, autodie\fR at
<http://perltraining.com.au/tips/2008\-08\-20.html>
.SH "ACKNOWLEDGEMENTS"
.IX Header "ACKNOWLEDGEMENTS"
Mark Reed and Roland Giersig \*(-- Klingon translators.
.PP
See the \fI\s-1AUTHORS\s0\fR file for full credits. The latest version of this
file can be found at
<https://github.com/pjf/autodie/tree/master/AUTHORS> .