$ cat et.pl
#!/usr/bin/env perl 
use strict;
use warnings;
use Expect ();

my $spawn = expect->spawn("foo $_");
$ perl et.pl 
Use of uninitialized value $_ in concatenation (.) or string at et.pl line 6.
Can't locate object method "spawn" via package "expect" (perhaps you forgot to load "expect"?) at et.pl line 6.