path: root/upstream/debian-unstable/man3/autodie.3perl

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.\" ========================================================================
.\"
.IX Title "autodie 3perl"
.TH autodie 3perl 2024-05-30 "perl v5.38.2" "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 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 "BUGS"
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 \fBdoes not check calls to \fR\f(CB\*(C`print\*(C'\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 { $cmd } @args\*(C'\fR
to be considered a syntax error until the end of the lexical scope.
If you really need to use the exotic form, you can call \f(CW\*(C`CORE::system\*(C'\fR
or \f(CW\*(C`CORE::exec\*(C'\fR instead, or use \f(CW\*(C`no autodie qw(system exec)\*(C'\fR before
calling the exotic form.
.SH GOTCHAS
.IX Header "GOTCHAS"
Functions called in list context are assumed to have failed if they
return an empty list, or a list consisting only of a single undef
element.
.PP
Some builtins (e.g. \f(CW\*(C`chdir\*(C'\fR or \f(CW\*(C`truncate\*(C'\fR) has a call signature that
cannot completely be represented with a Perl prototype.  This means
that some valid Perl code will be invalid under autodie.  As an example:
.PP
.Vb 1
\&  chdir(BAREWORD);
.Ve
.PP
Without autodie (and assuming BAREWORD is an open
filehandle/dirhandle) this is a valid call to chdir.  But under
autodie, \f(CW\*(C`chdir\*(C'\fR will behave like it had the prototype ";$" and thus
BAREWORD will be a syntax error (under "use strict".  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 "DIAGNOSTICS" in Fatal.
.SH "Tips and Tricks"
.IX Header "Tips and Tricks"
.SS "Importing autodie into another namespace than ""caller"""
.IX Subsection "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.
.SH BUGS
.IX Header "BUGS"
"Used only once" 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 "lose" 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 "REPORTING BUGS"
.IX Subsection "REPORTING BUGS"
Please report bugs via the GitHub Issue Tracker at
<https://github.com/pjf/autodie/issues>.
.SH FEEDBACK
.IX Header "FEEDBACK"
If you find this module useful, please consider rating it on the
CPAN 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 \fIAUTHORS\fR file for full credits.  The latest version of this
file can be found at
<https://github.com/pjf/autodie/tree/master/AUTHORS> .