How do I send a header to my Web server (such as Nginx / Lighttpd / Apache / ISS) on a Apple OS X or Unix or Linux based system using a curl command line option for testing and debugging my web apps or server nodes behind a load balancer?


The curl command supports -H or --header option to pass extra HTTP header to use when getting a web page from your web server. You may specify any number of extra headers. When you add a custom header that has the same name as one of the internal ones curl would use, your externally set header will be used instead of the internal one. The syntax is:

curl -H 'YOUR-EXTRA-HEADER-HERE' apache-server-ip
curl -H 'YOUR-EXTRA-HEADER-1-HERE' -H 'YOUR-EXTRA-HEADER-2-HERE' www.cyberciti.biz

For example, send Host header to www.cyberciti.biz to get HTML response from 75.126.153.206:80, run:

curl -H 'Host: www.cyberciti.biz' 75.126.153.206:80

This is also useful when 75.126.153.206 has multiple virtual host set. The default is not to response anything when virtual host header is not sent:
$ curl -I 75.126.153.206:80
Sample outputs:

HTTP/1.1 500 Internal Server Error
Server: nginx
Date: Wed, 31 Oct 2012 18:51:03 GMT
Content-Type: text/html
Connection: keep-alive
X-Whom: l1-biz-cyber

Now, sent www.cyberciti.biz as Host header:
$ curl -I -H 'Host: www.cyberciti.biz' 75.126.153.206:80
Sample outputs:

HTTP/1.1 200 OK
Server: nginx
Date: Wed, 31 Oct 2012 18:52:20 GMT
Content-Type: text/html
Connection: keep-alive
X-Whom: l2-com-cyber
Vary: Cookie
Last-Modified: Wed, 31 Oct 2012 18:48:58 GMT
Cache-Control: max-age=98, must-revalidate
X-Galaxy: Andromeda-1
X-Origin-Type: DynamicViaDAL

You can use this command to test Apache server node behind a load balancer (only work with your own VLAN/LAN setup):

## see if 192.168.1.11:95 apache node #1 is working or not ##
curl -I --header 'Host: www.cyberciti.biz' 'http://192.168.1.11:95/'

Sample outputs:

HTTP/1.1 200 OK
X-Whom: l1-com-cyber
Vary: Cookie
Last-Modified: Wed, 31 Oct 2012 18:54:00 GMT
Cache-Control: max-age=77, must-revalidate
Content-type: text/html
Date: Wed, 31 Oct 2012 18:57:43 GMT
Server: lighttpd

This option can be used multiple times to add/replace/remove multiple headers:

curl www.cyberciti.biz \ 
-H "Accept-Language: en" \ 
-H "Host www.cyberciti.biz" \ 
-H "User-Agent: curl"

References

See curl command man page for more options:
$ man curl