autodie(3) - Linux man page

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
}

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 surety that no behavorial 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

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

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.

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)".
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 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/master/AUTHORS> .