sub blah
{
    my %args=(@_);
    foreach my $needed (qw( foo bar baz )) {
        exists $args{$needed} or die "blah() needs a $needed parameter";
    }
    # ....
}

blah(foo => 42, bar => "don't forget this", baz => 'oh!');
blah(foo => 42, baz => 'oh!'); # <-- will die()

##</code><code>##

$foo=42;
print nameThatVariable($foo); # '$foo', of course.

$foo=[ 42 ];
print nameThatVariable($foo); # still '$foo'.

@bar=( 42 );
print nameThatVariable(@bar); # '@bar', of course.

$baz=$foo=\@bar;
print nameThatVariable($foo); # 'reference to @bar' or '$foo'?
print nameThatVariable($baz); # 'reference to @bar' or '$foo' or '$baz' ?

print nameThatVariable(\@bar); # 'reference to @bar'?

print nameThatVariable(do { my $tmp=23 }); # '$tmp'?

print nameThatVariable([ 23,45 ]); # ?