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);

##</code><code>##

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