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autodie::exception(3pm)Perl Programmers Reference Guideautodie::exception(3pm)


       autodie::exception - Exceptions from autodying functions.


           eval {
               use autodie;

               open(my $fh, '<', 'some_file.txt');


           if (my $E = $@) {
               say "Ooops!  ",$E->caller," had problems: $@";


       When an autodie enabled function fails, it generates an
       "autodie::exception" object.  This can be interrogated to determine
       further information about the error that occurred.

       This document is broken into two sections; those methods that are most
       useful to the end-developer, and those methods for anyone wishing to
       subclass or get very familiar with "autodie::exception".

   Common Methods
       These methods are intended to be used in the everyday dealing of

       The following assume that the error has been copied into a separate

           if ($E = $@) {

       This is not required, but is recommended in case any code is called
       which may reset or alter $@.


           my $array_ref = $E->args;

       Provides a reference to the arguments passed to the subroutine that


           my $sub = $E->function;

       The subroutine (including package) that threw the exception.


           my $file = $E->file;

       The file in which the error occurred (eg, "" or


           my $package = $E->package;

       The package from which the exceptional subroutine was called.


           my $caller = $E->caller;

       The subroutine that called the exceptional code.


           my $line = $E->line;

       The line in "$E->file" where the exceptional code was called.


           my $context = $E->context;

       The context in which the subroutine was called by autodie; usually the
       same as the context in which you called the autodying subroutine.  This
       can be 'list', 'scalar', or undefined (unknown).  It will never be
       'void', as "autodie" always captures the return value in one way or

       For some core functions that always return a scalar value regardless of
       their context (eg, "chown"), this may be 'scalar', even if you used a
       list context.


           my $return_value = $E->return;

       The value(s) returned by the failed subroutine.  When the subroutine
       was called in a list context, this will always be a reference to an
       array containing the results.  When the subroutine was called in a
       scalar context, this will be the actual scalar returned.


           my $errno = $E->errno;

       The value of $! at the time when the exception occurred.

       NOTE: This method will leave the main "autodie::exception" class and
       become part of a role in the future.  You should only call "errno" for
       exceptions where $! would reasonably have been set on failure.


           my $old_eval_error = $E->eval_error;

       The contents of $@ immediately after autodie triggered an exception.
       This may be useful when dealing with modules such as Text::Balanced
       that set (but do not throw) $@ on error.


           if ( $e->matches('open') ) { ... }

           if ( 'open' ~~ $e ) { ... }

       "matches" is used to determine whether a given exception matches a
       particular role.

       An exception is considered to match a string if:

       o   For a string not starting with a colon, the string exactly matches
           the package and subroutine that threw the exception.  For example,
           "MyModule::log".  If the string does not contain a package name,
           "CORE::" is assumed.

       o   For a string that does start with a colon, if the subroutine
           throwing the exception does that behaviour.  For example, the
           "CORE::open" subroutine does ":file", ":io" and ":all".

           See "CATEGORIES" in autodie for further information.

           On Perl 5.10 and above, using smart-match ("~~") with an
           "autodie::exception" object will use "matches" underneath.  This
           module used to recommend using smart-match with the exception
           object on the left hand side, but in future Perls that is likely to
           stop working.  The smart-match facility of this class should only
           be used with the exception object on the right hand side.  Having
           the exception object on the right is both future-proof and portable
           to older Perls, back to 5.10.  Beware that this facility can only
           be relied upon when it is certain that the exception object
           actually is an "autodie::exception" object; it is no more capable
           than an explicit call to the "matches" method.

   Advanced methods
       The following methods, while usable from anywhere, are primarily
       intended for developers wishing to subclass "autodie::exception", write
       code that registers custom error messages, or otherwise work closely
       with the "autodie::exception" model.


           autodie::exception->register( 'CORE::open' => \&mysub );

       The "register" method allows for the registration of a message handler
       for a given subroutine.  The full subroutine name including the package
       should be used.

       Registered message handlers will receive the "autodie::exception"
       object as the first parameter.


           say "Problem occurred",$@->add_file_and_line;

       Returns the string " at %s line %d", where %s is replaced with the
       filename, and %d is replaced with the line number.

       Primarily intended for use by format handlers.


           say "The error was: ",$@->stringify;

       Formats the error as a human readable string.  Usually there's no
       reason to call this directly, as it is used automatically if an
       "autodie::exception" object is ever used as a string.

       Child classes can override this method to change how they're


           my $error_string = $E->format_default;

       This produces the default error string for the given exception, without
       using any registered message handlers.  It is primarily intended to be
       called from a message handler when they have been passed an exception
       they don't want to format.

       Child classes can override this method to change how default messages
       are formatted.


           my $error = autodie::exception->new(
               args => \@_,
               function => "CORE::open",
               errno => $!,
               context => 'scalar',
               return => undef,

       Creates a new "autodie::exception" object.  Normally called directly
       from an autodying function.  The "function" argument is required, its
       the function we were trying to call that generated the exception.  The
       "args" parameter is optional.

       The "errno" value is optional.  In versions of "autodie::exception"
       1.99 and earlier the code would try to automatically use the current
       value of $!, but this was unreliable and is no longer supported.

       Atrributes such as package, file, and caller are determined
       automatically, and cannot be specified.


       autodie(3), autodie::exception::system(3)


       Copyright (C)2008 Paul Fenwick

       This is free software.  You may modify and/or redistribute this code
       under the same terms as Perl 5.10 itself, or, at your option, any later
       version of Perl 5.


       Paul Fenwick <>

perl v5.28.1                      2018-11-01           autodie::exception(3pm)

perl 5.28.1 - Generated Mon Jan 14 18:05:48 CST 2019
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