autodie

Section: Perl Programmers Reference Guide (3perl)
Updated: 2019-04-20
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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(: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 <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> .


 

Index

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
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