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

       carp    - warn of errors (from perspective of caller)

       cluck   - warn of errors with stack backtrace
		 (not exported by default)

       croak   - die of errors (from perspective of caller)

       confess - die of errors with stack backtrace

       shortmess - return the message that carp and croak produce

       longmess - return the message that cluck and confess produce

	   use Carp;
	   croak "We're outta here!";

	   use Carp qw(cluck);
	   cluck "This is how we got here!";

	   print FH Carp::shortmess("This will have caller's details added");
	   print FH Carp::longmess("This will have stack backtrace added");

       The Carp routines are useful in your own modules because they act like die() or warn(),
       but with a message which is more likely to be useful to a user of your module.  In the
       case of cluck, confess, and longmess that context is a summary of every call in the
       call-stack.  For a shorter message you can use carp, croak or shortmess which report the
       error as being from where your module was called.  There is no guarantee that that is
       where the error was, but it is a good educated guess.

       Here is a more complete description of how shortmess works.  What it does is search the
       call-stack for a function call stack where it hasn't been told that there shouldn't be an
       error.  If every call is marked safe, it then gives up and gives a full stack backtrace
       instead.  In other words it presumes that the first likely looking potential suspect is
       guilty.	Its rules for telling whether a call shouldn't generate errors work as follows:

       1.  Any call from a package to itself is safe.

       2.  Packages claim that there won't be errors on calls to or from packages explicitly
	   marked as safe by inclusion in @CARP_NOT, or (if that array is empty) @ISA.	The abil-
	   ity to override what @ISA says is new in 5.8.

       3.  The trust in item 2 is transitive.  If A trusts B, and B trusts C, then A trusts C.
	   So if you do not override @ISA with @CARP_NOT, then this trust relationship is identi-
	   cal to, "inherits from".

       4.  Any call from an internal Perl module is safe.  (Nothing keeps user modules from mark-
	   ing themselves as internal to Perl, but this practice is discouraged.)

       5.  Any call to Carp is safe.  (This rule is what keeps it from reporting the error where
	   you call carp/croak/shortmess.)

       Forcing a Stack Trace

       As a debugging aid, you can force Carp to treat a croak as a confess and a carp as a cluck
       across all modules. In other words, force a detailed stack trace to be given.  This can be
       very helpful when trying to understand why, or from where, a warning or error is being

       This feature is enabled by 'importing' the non-existent symbol 'verbose'. You would typi-
       cally enable it by saying

	   perl -MCarp=verbose script.pl

       or by including the string "MCarp=verbose" in the PERL5OPT environment variable.

       The Carp routines don't handle exception objects currently.  If called with a first argu-
       ment that is a reference, they simply call die() or warn(), as appropriate.

perl v5.8.0				    2002-06-01					Carp(3pm)
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