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.
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. (Noth
ing 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.plor by including the string "MCarp=verbose" in the PERL5OPT
environment variable.
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.