#!/usr/bin/perl

use strict;
use warnings;
use 5.010; # only for // and say

sub failing_func
{
	$!=shift;
	return undef;
}

sub defined_or_warn
{
	my ($value,$error)=@_;
	return $value if defined $value;
	warn $error;
}

sub defined_or_warn_reverse
{
	my ($error,$value)=@_;
	return $value if defined $value;
	warn $error;
}

$!=1; say "error 1 => $!";
$!=2; say "error 2 => $!";
$!=3; say "error 3 => $!";
my $v=failing_func(1) // warn "oops: $!"; # should give error 1
$v=defined_or_warn(failing_func(2),"oops: $!"); # should give error 2
$v=defined_or_warn_reverse("oops: $!",failing_func(3)); # should give error 3

##</code><code>##

error 1 => Operation not permitted
error 2 => No such file or directory
error 3 => No such process
oops: Operation not permitted at foo.pl line 31.
oops: No such file or directory at foo.pl line 17.
oops: No such file or directory at foo.pl line 24.