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autodie(3pm)           Perl Programmers Reference Guide           autodie(3pm)




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:

       o   The command does not start.

       o   The command is killed by a signal.

       o   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(3), autodie::exception(3), autodie::hints(3),
       IPC::System::Simple(3)

       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> .



perl v5.24.0                      2016-03-01                      autodie(3pm)

perl 5.24 - Generated Wed Nov 2 19:26:22 CDT 2016
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