See the current Perl documentation for caller.
Here is our local, out-dated (pre-5.6) version:
caller - get context of the current subroutine call
Returns the context of the current subroutine call. In scalar context, returns the caller's package name if there is a caller, that is, if we're in a subroutine or eval() or require(), and the undefined value otherwise. In list context, returns
($package, $filename, $line) = caller;
With EXPR, it returns some extra information that the debugger uses to print a stack trace. The value of EXPR indicates how many call frames to go back before the current one.
($package, $filename, $line, $subroutine, $hasargs, $wantarray, $evaltext, $is_require) = caller($i);
$subroutine may be
"(eval)" if the frame is not a subroutine call, but an eval(). In such a case additional elements
$is_require are set:
$is_require is true if the frame is created by a
require or use statement,
$evaltext contains the text of the
eval EXPR statement. In particular, for a
eval BLOCK statement,
$evaltext is undefined. (Note also that each use statement creates a require frame inside an
eval EXPR) frame.
Furthermore, when called from within the
DB package, caller returns more detailed information:
it sets the list variable
@DB::args to be the arguments with which the subroutine was invoked.
Be aware that the optimizer might have optimized call frames away before
caller() had a chance to get the information. That means that caller(N)
might not return information about the call frame you expect it do, for
N > 1. In particular,
@DB::args might have information from the previous time caller() was called.