Returns the context of the current pure perl 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. caller never returns XS subs and they are skipped. The next pure perl sub will appear instead of the XS sub in caller's return values. In list context, caller returns
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.
Here, $subroutine is the function that the caller called (rather than the
function containing the caller).  Note that $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
require or 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.
$hints
 and $bitmask
 contain pragmatic hints that the caller was
compiled with.  $hints
 corresponds to $^H , and
$bitmask
 corresponds to
${^WARNING_BITS} .  The $hints
 and
$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
undef if %^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 in
list context, and with an argument, 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.
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 @_ , so
@DB::args
 will contain modifications the subroutine makes to
@_  or its contents, not the original values at call
time.  @DB::args
, like @_ , 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::args
 is actually a hybrid of the current state and initial state
of @_ .  Buyer beware.