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
require) and the undefined value otherwise. In list context, returns
# 0 1 2 ($package, $filename, $line) = caller;
With EXPR, it returns some extra information that the debugger uses to print a stack trace. The value of EXPR indicates how many call frames to go back before the current one.
# 0 1 2 3 4 ($package, $filename, $line, $subroutine, $hasargs, # 5 6 7 8 9 10 $wantarray, $evaltext, $is_require, $hints, $bitmask, $hinthash) = caller($i);
Here $subroutine may be
(eval) if the frame is not a subroutine call, but an
eval. In such a case additional elements $evaltext and
$is_require are set:
$is_require is true if the frame is created by a
use statement, $evaltext contains the text of the
eval EXPR statement. In particular, for an
eval BLOCK statement, $subroutine is
(eval), but $evaltext is undefined. (Note also that each
use statement creates a
require frame inside an
eval EXPR frame.) $subroutine may also be
(unknown) if this particular subroutine happens to have been deleted from the symbol table.
$hasargs is true if a new instance of
@_ was set up for the frame.
$bitmask contain pragmatic hints that the caller was compiled with. The
$bitmask values are subject to change between versions of Perl, and are not meant for external use.
$hinthash is a reference to a hash containing the value of
%^H when the caller was compiled, or
%^H was empty. Do not modify the values of this hash, as they are the actual values stored in the optree.
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 to, for
N > 1. In particular,
@DB::args might have information from the previous time
caller was called.
Also be aware that setting
@DB::args is best effort, intended for debugging or generating backtraces, and should not be relied upon. In particular, as
@_ contains aliases to the caller's arguments, Perl does not take a copy of
@DB::args will contain modifications the subroutine makes to
@_ or its contents, not the original values at call time.
@_, does not hold explicit references to its elements, so under certain cases its elements may have become freed and reallocated for other variables or temporary values. Finally, a side effect of the current implementation means that the effects of
shift @_ can normally be undone (but not
pop @_ or other splicing, and not if a reference to
@_ has been taken, and subject to the caveat about reallocated elements), so
@DB::args is actually a hybrid of the current state and initial state of
@_. Buyer beware.