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



NAME
       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 pro-
       duce

SYNOPSIS
           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");

DESCRIPTION
       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.

       You can also alter the way the output and logic of "Carp"
       works, by changing some global variables in the "Carp"
       namespace. See the section on "GLOBAL VARIABLES" below.

       Here is a more complete description of how shortmess
       works.  What it does is search the call-stack for a func-
       tion 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 inclu-
           sion in @CARP_NOT, or (if that array is empty) @ISA.
           The ability 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 over-
           ride @ISA with @CARP_NOT, then this trust relationship
           is identical to, "inherits from".

       4.  Any call from an internal Perl module is safe.
           (Nothing keeps user modules from marking 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 generated.

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

           perl -MCarp=verbose script.pl

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

       Alternately, you can set the global variable $Carp::Ver-
       bose to true.  See the "GLOBAL VARIABLES" section below.

GLOBAL VARIABLES
       $Carp::CarpLevel

       This variable determines how many call frames are to be
       skipped when reporting where an error occurred on a call
       to one of "Carp"'s functions. For example:

           $Carp::CarpLevel = 1;
           sub bar     { .... or _error('Wrong input') }
           sub _error  { Carp::carp(@_) }

       This would make Carp report the error as coming from
       "bar"'s caller, rather than from "_error"'s caller, as it
       normally would.

       Defaults to 0.

       $Carp::MaxEvalLen

       This variable determines how many characters of a string-
       eval are to be shown in the output. Use a value of 0 to
       show all text.

       Defaults to 0.

       $Carp::MaxArgLen

       This variable determines how many characters of each argu-
       ment to a function to print. Use a value of 0 to show the
       full length of the argument.

       Defaults to 64.

       $Carp::MaxArgNums

       This variable determines how many arguments to each func-
       tion to show.  Use a value of 0 to show all arguments to a
       function call.

       Defaults to 8.

       $Carp::Verbose

       This variable makes "Carp" use the "longmess" function at
       all times.  This effectively means that all calls to
       "carp" become "cluck" and all calls to "croak" become
       "confess".

       Note, this is analogous to using "use Carp 'verbose'".

       Defaults to 0.

BUGS
       The Carp routines don't handle exception objects cur-
       rently.  If called with a first argument that is a refer-
       ence, they simply call die() or warn(), as appropriate.



perl v5.8.8                 2001-09-21                    Carp(3)