$ cat foo.cgi
#!/usr/bin/env perl
use strict;
use warnings;
use CGI::Tiny;

cgi {
	my $cgi = $_;
	my $bookparam = $cgi->param('book') || '';
	$cgi->render (text => "bookparam is $bookparam\n");
}
$ (export QUERY_STRING='book=bar'; ./foo.cgi)
Date: Mon, 12 Dec 2022 13:57:29 GMT
Content-Type: text/plain;charset=UTF-8
Content-Length: 17

bookparam is bar
$ ./foo.cgi 
Date: Mon, 12 Dec 2022 14:01:26 GMT
Content-Type: text/plain;charset=UTF-8
Content-Length: 14

bookparam is 
$