autodie(3p) | Perl Programmers Reference Guide | autodie(3p)

# 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:

        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 represented 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.

# Tips and Tricks

## 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.

# 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>.

# FEEDBACK

If you find this module useful, please consider rating it on metacpan at <https://metacpan.org/pod/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

Copyright 2008-2009, Paul Fenwick <pjf@perltraining.com.au>

# 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> .

2025-01-28 | perl v5.40.1