# Foo.pm

my $shell = $ENV{'SHELL'} || "";

BEGIN {
    if ( $ENV{'SHELL'}) {
        print "\$ENV{'SHELL'} is $ENV{'SHELL'}...\n";
    } else {
        print "\$ENV{'SHELL'} is not set...\n";
    }
    if ( $shell ) {
        print "\$shell is $shell...\n";
    } else {
        print "\$shell is not set...\n";
    }
}

1;

##</code><code>##

#!/usr/bin/perl
use Foo;
print "done.\n";