comment on

Stumped! Can anyone shed any light?

Yeah, what BrowserUk said, websites can do whatever they want, for example, a local http echo server

$ lwp-request -E http://127.0.0.1:80
GET http://127.0.0.1:80
User-Agent: lwp-request/6.15 libwww-perl/6.15

200 Assumed OK
Client-Date: Thu, 16 Jun 2016 23:35:40 GMT
Client-Peer: 127.0.0.1:80
Client-Response-Num: 1

Echo: GET / HTTP/1.1
Echo: TE: deflate,gzip;q=0.3
Echo: Connection: TE, close
Echo: Host: 127.0.0.1:80
Echo: User-Agent: lwp-request/6.15 libwww-perl/6.15
Echo:

$ lwp-request -E http://127.0.0.1:80 -HHost:Host
GET http://127.0.0.1:80
Host: Host
User-Agent: lwp-request/6.15 libwww-perl/6.15

200 Assumed OK
Client-Date: Thu, 16 Jun 2016 23:35:42 GMT
Client-Peer: 127.0.0.1:80
Client-Response-Num: 1

Echo: GET / HTTP/1.1
Echo: TE: deflate,gzip;q=0.3
Echo: Connection: TE, close
Echo: Host: Host
Echo: User-Agent: lwp-request/6.15 libwww-perl/6.15
Echo:
[download]

So you see the "host" header was added successfully and returned

With the real website example.com it works exactly the same

$ lwp-request -E http://93.184.216.34:80
GET http://93.184.216.34:80
User-Agent: lwp-request/6.15 libwww-perl/6.15

404 Not Found
Connection: close
Date: Thu, 16 Jun 2016 23:26:51 GMT
Server: ECS (rhv/81A7)
Content-Length: 345
Content-Type: text/html
Client-Date: Thu, 16 Jun 2016 23:37:48 GMT
Client-Peer: 93.184.216.34:80
Client-Response-Num: 1
Title: 404 - Not Found

<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
         "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
        <head>
                <title>404 - Not Found</title>
        </head>
        <body>
                <h1>404 - Not Found</h1>
        </body>
</html>

$ lwp-request -E http://93.184.216.34:80 -Hhost:example.com
GET http://93.184.216.34:80
Host: example.com
User-Agent: lwp-request/6.15 libwww-perl/6.15

200 OK
Cache-Control: max-age=604800
Connection: close
Date: Thu, 16 Jun 2016 23:27:01 GMT
Accept-Ranges: bytes
ETag: "359670651"
Server: ECS (rhv/81A7)
Vary: Accept-Encoding
Content-Length: 1270
Content-Type: text/html
Expires: Thu, 23 Jun 2016 23:27:01 GMT
Last-Modified: Fri, 09 Aug 2013 23:54:35 GMT
Client-Date: Thu, 16 Jun 2016 23:37:58 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

<!doctype html>
<html>
<head>
    <title>Example Domain</title>
...
[download]

If you do lwp-request -E http://google.com you'll get a redirect to http://www.google.com

If you do lwp-request -E http://google.com -HHost:Host google won't redirect it will just return 404

websits can do what they want

In reply to Re: Adding a 'Host' request header leads to unexpected LWP::UserAgent behaviour (proof example.com) by Anonymous Monk
in thread Adding a 'Host' request header leads to unexpected LWP::UserAgent behaviour by tomgracey

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