Carp::Clan Perl module
This module is based on "'Carp.pm'" from Perl 5.005_03. It has been
modified to skip all package names matching the pattern given in the "use"
statement inside the "'qw()'" term (or argument list).
Suppose you have a family of modules or classes named "Pack::A", "Pack::B"
and so on, and each of them uses "'Carp::Clan qw(^Pack::);'" (or at least
the one in which the error or warning gets raised).
Thus when for example your script "tool.pl" calls module "Pack::A", and
module "Pack::A" calls module "Pack::B", an exception raised in module
"Pack::B" will appear to have originated in "tool.pl" where "Pack::A" was
called, and not in "Pack::A" where "Pack::B" was called, as the unmodified
"'Carp.pm'" would try to make you believe ':-)'.
This works similarly if "Pack::B" calls "Pack::C" where the exception is
In other words, this blames all errors in the "'Pack::*'" modules on the
user of these modules, i.e., on you. ';-)'
The skipping of a clan (or family) of packages according to a pattern
describing its members is necessary in cases where these modules are not
classes derived from each other (and thus when examining '@ISA' - as in the
original "'Carp.pm'" module - doesn't help).
The purpose and advantage of this is that a "clan" of modules can work
together (and call each other) and throw exceptions at various depths down
the calling hierarchy and still appear as a monolithic block (as though
they were a single module) from the perspective of the caller.
In case you just want to ward off all error messages from the module in
which you "'use Carp::Clan'", i.e., if you want to make all error messages
or warnings to appear to originate from where your module was called (this
is what you usually used to "'use Carp;'" for ';-)'), instead of in your
module itself (which is what you can do with a "die" or "warn" anyway), you
do not need to provide a pattern, the module will automatically provide the
correct one for you.
I.e., just "'use Carp::Clan;'" without any arguments and call "carp" or
"croak" as appropriate, and they will automatically defend your module
against all blames!
In other words, a pattern is only necessary if you want to make several
modules (more than one) work together and appear as though they were only
Forcing a Stack Trace
As a debugging aid, you can force "'Carp::Clan'" to treat a "croak" as
a "confess" and a "carp" as a "cluck". 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 either by "importing" the non-existent symbol
'verbose', or by setting the global variable "'$Carp::Clan::Verbose'"
to a true value.
You would typically enable it by saying
use Carp::Clan qw(verbose);
Note that you can both specify a "family pattern" and the string
"verbose" inside the "'qw()'" term (or argument list) of the "use"
statement, but consider that a pattern of packages to skip is pointless
when "verbose" causes a full stack trace anyway.