Carp

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 produce

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 guaran-
       tee 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 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 pack-
           ages explicitly marked as safe by inclusion 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 override @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 prac-
           tice is discouraged.)

       5.  Any call to Carp is safe.  (This rule is what keeps it from report-
           ing 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 gener-
       ated.

       This feature is enabled by 'importing' the non-existent symbol 'ver-
       bose'. 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::Verbose 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 func-
       tions. 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 argument 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 function 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 currently.  If called
       with a first argument that is a reference, they simply call die() or
       warn(), as appropriate.



perl v5.8.6                       2001-09-21                           Carp(3)