[pm-h] Binding variables to a reference

[Todd Rinaldo]

This has been driving me crazy, so I have to ask how (and/or if) this
can be done. I have the below program. If you run it, bar prints out.
This exemplifies how you can alter the variables that were passed to a
target subroutine. substr does this but I suspect it's more a result
of magic C code than magic Perl code.

my $foo = 'foo';
bar($foo);
print "$foo\n";
exit;

sub bar {
   $_[0] = 'bar';
}

My question, How do I do something like this and get it to print out bar?

my $foo = 'foo';
bar($foo);
print "$foo\n";
exit;

sub bar {
   my \$bar = \$_[0];
   $bar = 'bar';
}

Todd