Devel::DollarAt(3pm)					User Contributed Perl Documentation				      Devel::DollarAt(3pm)

NAME

       Devel::DollarAt - Give magic abilities to $@

SYNOPSIS

	   use Devel::DollarAt;

	   eval "0/0";
	   print $@, $@->backtrace;
	   $@->redie;

DESCRIPTION

       Using eval {}, you may catch Perl exceptions almost like you do it with try {} in Java.	However there are days when you miss some features
       of exceptions.  The only thing you know about the error that occured is the string $@, which combines the error message and technical data
       like the line number.

       The Devel::DollarAt module gives some functionality to the $@ scalar.  Once you say "use Devel::DollarAt", the module is active program-
       wide.  If an exception occurs anywhere in any module, $@ will be globally set to an object of class Devel::DollarAt.  Apart from
       performance, this shouldn't be a problem because $@ tries to be downwardly compatible to the normal $@.	However using this package in CPAN
       modules or large software projects is discouraged.

DISCLAIMER

       Use this module only for debugging.  Don't think of it as an exception framework for Perl or something like that.  It just gives magic
       abilities to $@, that's all.

METHODS

       backtrace
	       Returns a Devel::Backtrace object, which lets you inspect the callers of the fatality.

       filename
	       Returns the name of the file in which the error occured.

       inputhandle
	       Returns the file handle which has most recently be read from at the time of the error.

       inputline
	       Returns the line number of "$@->inputhandle" (which is $.) at the time of the error.

       line    Returns the number of the line in which the error occured.

       redie   Redispatches this exception to the next eval{}.

       redispatch_points
	       Returns a list of objects with informations about when this exception was redispatched.	Each object has got the accessors
	       "package", "filename" and "line".  In string context, the objects will look like "redispatched from FooPackage at file.pl:17
".

       to_string
	       Returns a string that looks quite like the normal $@, e. g. "Illegal division by zero at foo.pl line 42, <> line 13."
	       Devel::DollarAt overloads the "" (stringification) operator to this method.

EXAMPLES

       A very simple (and pointless) way to use Devel::DollarAt is this oneliner:

	   perl -MDevel::DollarAt -e '0/0'

       It bails out with "Illegal division by zero at -e line 1." and an exit status of 1, just like it would have done if you hadn't supplied
       -MDevel::DollarAt.  This is because the magically modified $@ variable gets stringified when perl prints it as exit reason.  If you
       actually want to see the difference, use

	   perl -MDevel::DollarAt=frame -e '0/0'

       This bails out with "[[Illegal division by zero at -e line 1.]]" so you can see that something has happened.

KNOWN PROBLEMS

       This module requires that no other code tampers with $SIG{__DIE__} or *CORE::GLOBAL::die.

       A not widely known feature of Perl is that it can propagate $@.	If you call die() without parameters or with an empty string or an
       undefined value, the error message will be "Died".  However, if $@ was set to some value before this, the previous error message will be
       used with "	...propagated" appended:

	   perl -e '$@="7"; die"
	   7	   ...propagated at -e line 1.

       Devel::DollarAt emulates this behaviour.

       If you use the above example but leave out the double quotes, perl's behaviour is different as of version 5.8.8:

	   perl -e '$@=7; die'
	   7 at -e line 1.

       Devel::DollarAt does not emulate this behaviour:

	   perl -MDevel::DollarAt -e '$@=7; die'
	   7	   ...propagated at -e line 1.

       If a previous $@ is propagated, inputhandle and inputline won't work.  They won't be interpolated into the stringified $@, either.

       If perl comes across syntax errors, $@ appears to be just a string as usual.  Apparently $SIG{__DIE__} won't be called for syntax errors.

AUTHOR

       Christoph Bussenius <pepe@cpan.org>

       If you use this module, I'll be glad if you drop me a note.  You should mention this module's name in the subject of your mails, in order
       to make sure they won't get lost in all the spam.

LICENSE

       This module is in the public domain.

       If your country's law does not allow this module being in the public domain or does not include the concept of public domain, you may use
       the module under the same terms as perl itself.

perl v5.10.0							    2009-01-27						      Devel::DollarAt(3pm)