caller() mystery

[rovf]

It seems that I haven't understood properly the perldocs of the caller function. My understanding was that with caller(1), I walk up one frame (i.e. get the information about who is calling me), with caller(2) I walk up 2 frames, etc.

But now look at the following example program. _format_caller is called twice; the first time it is supposed to print what is returned by caller(1), the second time caller(2).

use strict;
use warnings;

sub _format_caller {
  my @x=caller($_[0]);
  print "elements:",scalar(@x),"\n";
  print(join(',',@x),"\n");
}

sub f {
  my $level=$_[0];
  print "test caller $level\n";
  _format_caller($level);
}

f(1);
f(2);

The actual printout looks like this:

>
Use of uninitialized value in join or string at U:\develsv\ARTS\playgr
+ound\callertest.pl line 7.
Use of uninitialized value in join or string at U:\develsv\ARTS\playgr
+ound\callertest.pl line 7.
Use of uninitialized value in join or string at U:\develsv\ARTS\playgr
+ound\callertest.pl line 7.
test caller 1
elements:10
main,U:\develsv\ARTS\playground\callertest.pl,16,main::f,1,,,,2,UUUUUU
+UUUUU
test caller 2
elements:0

Well, the uninitialized warnings are because some of the elements returned by caller are undef. But why don't I get anything back in the case of caller(2)?