autodie

CONTENTS

• NAME
• SYNOPSIS
• DESCRIPTION
• EXCEPTIONS
• CATEGORIES
• FUNCTION SPECIFIC NOTES
  • print
  • flock
  • system/exec
• GOTCHAS
• DIAGNOSTICS
• BUGS
  • autodie and string eval
  • REPORTING BUGS
• FEEDBACK
• AUTHOR
• LICENSE
• SEE ALSO
• ACKNOWLEDGEMENTS

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:

use feature qw(switch);

eval {
    use autodie;

    open(my $fh, '<', $some_file);

    my @records = <$fh>;

    # Do things with @records...

    close($fh);

};

given ($@) {
    when (undef)   { say "No error";                    }
    when ('open')  { say "Error from open";             }
    when (':io')   { say "Non-open, IO error.";         }
    when (':all')  { say "All other autodie errors."    }
    default        { say "Not an autodie error at all." }
}

Under Perl 5.8, the given/when structure is not available, so the following structure may be used:

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 representated 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.

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 or via the CPAN Request Tracker at https://rt.cpan.org/NoAuth/Bugs.html?Dist=autodie.

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 <[email protected]>.

AUTHOR

Copyright 2008-2009, Paul Fenwick <[email protected]>

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 .