$ lwp-request -USEd -H "Referer: http://localhost" http://example.com
GET http://example.com
Referer: http://localhost
User-Agent: lwp-request/6.15 libwww-perl/6.15

200 OK
Cache-Control: max-age=604800
Connection: close
Date: Sun, 29 Jan 2017 23:41:21 GMT
ETag: "359670651+ident"
Server: ECS (rhv/818F)
Vary: Accept-Encoding
Content-Length: 1270
Content-Type: text/html
Expires: Sun, 05 Feb 2017 23:41:21 GMT
Last-Modified: Fri, 09 Aug 2013 23:54:35 GMT
Client-Date: Sun, 29 Jan 2017 23:55:28 GMT
Client-Peer: 93.184.216.34:80
Client-Response-Num: 1
Title: Example Domain
X-Cache: HIT
X-Ec-Custom-Error: 1
X-Meta-Charset: utf-8
X-Meta-Viewport: width=device-width, initial-scale=1

##</code><code>##

use WWW::Mechanize;
my $ua = WWW::Mechanize->new;
$ua->get('http://example.com', 'Referer', 'localhost');
print $ua->res->request->headers_as_string;
print $ua->res->headers_as_string;
__END__
Accept-Encoding: gzip
Referer: localhost
User-Agent: WWW-Mechanize/1.78
Cache-Control: max-age=604800
Connection: close
Date: Sun, 29 Jan 2017 23:45:39 GMT
Accept-Ranges: bytes
ETag: "359670651"
Server: ECS (rhv/818F)
Vary: Accept-Encoding
Content-Encoding: gzip
Content-Length: 606
Content-Type: text/html
Expires: Sun, 05 Feb 2017 23:45:39 GMT
Last-Modified: Fri, 09 Aug 2013 23:54:35 GMT
Client-Date: Sun, 29 Jan 2017 23:59:46 GMT
Client-Peer: 93.184.216.34:80
Client-Response-Num: 1
X-Cache: HIT
X-Ec-Custom-Error: 1