autodie

Section: Perl Programmers Reference Guide (3pm)
Updated: 2010-10-12
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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(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
    }

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", "fileno", "open" and "sysopen".

The categories are currently:

    :all
        :default
            :io
                read
                seek
                sysread
                sysseek
                syswrite
                :dbm
                    dbmclose
                    dbmopen
                :file
                    binmode
                    close
                    fcntl
                    fileno
                    flock
                    ioctl
                    open
                    sysopen
                    truncate
                :filesys
                    chdir
                    closedir
                    opendir
                    link
                    mkdir
                    readlink
                    rename
                    rmdir
                    symlink
                    unlink
                :ipc
                    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 surity that no behavorial changes will occur if the "autodie" module is upgraded.

FUNCTION SPECIFIC NOTES

flock

It is not considered an error for "flock" to return false if it fails 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

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.

DIAGNOSTICS

:void cannot be used with lexical scope: The ":void" option is supported in Fatal, but not "autodie". However you can explicitly disable autodie end the end of the current block with "no autodie". To disable autodie for only a single function (eg, open) use or "no autodie qw(open)".

BUGS

``Used only once'' warnings can be generated when "autodie" or "Fatal" is used with package filehandles (eg, "FILE"). It's strongly recommended you use scalar filehandles instead.

Under Perl 5.8 only, "autodie" does not propagate into string "eval" statements, although it can be explicitly enabled inside a string "eval". This bug does not affect block "eval" statements in any version of Perl.

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 ue "Fatal" or "autodie" on other user subroutines will result in a compile-time error.

REPORTING BUGS

Please report bugs via the CPAN Request Tracker at <http://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 <pjf@perltraining.com.au>.

AUTHOR

LICENSE

This module is free software. You may distribute it under the same terms as Perl itself.

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 <http://github.com/pfenwick/autodie/tree/AUTHORS> .