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_requireis true if the frame is created by a
usestatement, $evaltext contains the text of the
eval EXPRstatement. In particular, for an
eval BLOCKstatement, $subroutine is
(eval), but $evaltext is undefined. (Note also that each
usestatement creates a
requireframe inside an
eval EXPRframe.) $subroutine may also be
(unknown)if this particular subroutine happens to have been deleted from the symbol table.
$hasargsis true if a new instance of
@_was set up for the frame.
$bitmaskcontain pragmatic hints that the caller was compiled with. The
$bitmaskvalues are subject to change between versions of Perl, and are not meant for external use.
$hinthashis a reference to a hash containing the value of
%^Hwhen the caller was compiled, or
%^Hwas 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::argsto be the arguments with which the subroutine was invoked.
Be aware that the optimizer might have optimized call frames away before
callerhad 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::argsmight have information from the previous time
Also be aware that setting
@DB::argsis 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::argswill 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 is 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::argsis actually a hybrid of the current state and initial state of
@_. Buyer beware.