Online: http://curl.haxx.se/docs/httpscripting.html
-Date: May 28, 2008
+Date: Jan 19, 2011
The Art Of Scripting HTTP Requests Using Curl
=============================================
request a particular action, and then the server replies a few text lines
before the actual requested content is sent to the client.
- Using curl's option --verbose (-v as a short option) will display what kind of
- commands curl sends to the server, as well as a few other informational texts.
- --verbose is the single most useful option when it comes to debug or even
- understand the curl<->server interaction.
+ The client, curl, sends a HTTP request. The request contains a method (like
+ GET, POST, HEAD etc), a number of request headers and sometimes a request
+ body. The HTTP server responds with a status line (indicating if things went
+ well), response headers and most often also a response body. The "body" part
+ is the plain data you requested, like the actual HTML or the image etc.
+
+ 1.1 See the Protocol
+
+ Using curl's option --verbose (-v as a short option) will display what kind
+ of commands curl sends to the server, as well as a few other informational
+ texts.
+
+ --verbose is the single most useful option when it comes to debug or even
+ understand the curl<->server interaction.
+
+ Sometimes even --verbose is not enough. Then --trace and --trace-ascii offer
+ even more details as they show EVERYTHING curl sends and receives. Use it
+ like this:
+
+ curl --trace-ascii debugdump.txt http://www.example.com/
2. URL
you get a web page returned in your terminal window. The entire HTML document
that that URL holds.
- All HTTP replies contain a set of headers that are normally hidden, use
- curl's --include (-i) option to display them as well as the rest of the
- document. You can also ask the remote server for ONLY the headers by using the
- --head (-I) option (which will make curl issue a HEAD request).
+ All HTTP replies contain a set of response headers that are normally hidden,
+ use curl's --include (-i) option to display them as well as the rest of the
+ document. You can also ask the remote server for ONLY the headers by using
+ the --head (-I) option (which will make curl issue a HEAD request).
4. Forms
And to use curl to post this form with the same data filled in as before, we
could do it like:
- curl --data "birthyear=1905&press=%20OK%20" http://www.hotmail.com/when/junk.cgi
+ curl --data "birthyear=1905&press=%20OK%20" \
+ http://www.example.com/when.cgi
This kind of POST will use the Content-Type
application/x-www-form-urlencoded and is the most widely used POST kind.
Put a file to a HTTP server with curl:
- curl --upload-file uploadfile http://www.uploadhttp.com/receive.cgi
+ curl --upload-file uploadfile http://www.example.com/receive.cgi
6. HTTP Authentication
To tell curl to use a user and password for authentication:
- curl --user name:password http://www.secrets.com
+ curl --user name:password http://www.example.com
The site might require a different authentication method (check the headers
returned by the server), and then --ntlm, --digest, --negotiate or even
Use curl to set the referer field with:
- curl --referer http://curl.haxx.se http://daniel.haxx.se
+ curl --referer http://www.example.come http://www.example.com
8. User Agent
is time to set the User Agent field to fool the server into thinking you're
one of those browsers.
- To make curl look like Internet Explorer on a Windows 2000 box:
+ To make curl look like Internet Explorer 5 on a Windows 2000 box:
- curl --user-agent "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)" [URL]
+ curl --user-agent "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)" [URL]
- Or why not look like you're using Netscape 4.73 on a Linux (PIII) box:
+ Or why not look like you're using Netscape 4.73 on an old Linux box:
- curl --user-agent "Mozilla/4.73 [en] (X11; U; Linux 2.2.15 i686)" [URL]
+ curl --user-agent "Mozilla/4.73 [en] (X11; U; Linux 2.2.15 i686)" [URL]
9. Redirects
To tell curl to follow a Location:
- curl --location http://www.sitethatredirects.com
+ curl --location http://www.example.com
If you use curl to POST to a site that immediately redirects you to another
page, you can safely use --location (-L) and --data/--form together. Curl will
The simplest way to send a few cookies to the server when getting a page with
curl is to add them on the command line like:
- curl --cookie "name=Daniel" http://www.cookiesite.com
+ curl --cookie "name=Daniel" http://www.example.com
Cookies are sent as common HTTP headers. This is practical as it allows curl
to record cookies simply by recording headers. Record cookies with curl by
using the --dump-header (-D) option like:
- curl --dump-header headers_and_cookies http://www.cookiesite.com
+ curl --dump-header headers_and_cookies http://www.example.com
(Take note that the --cookie-jar option described below is a better way to
store cookies.)
believing you had a previous connection). To use previously stored cookies,
you run curl like:
- curl --cookie stored_cookies_in_file http://www.cookiesite.com
+ curl --cookie stored_cookies_in_file http://www.example.com
Curl's "cookie engine" gets enabled when you use the --cookie option. If you
only want curl to understand received cookies, use --cookie with a file that
- doesn't exist. Example, if you want to let curl understand cookies from a page
- and follow a location (and thus possibly send back cookies it received), you
- can invoke it like:
+ doesn't exist. Example, if you want to let curl understand cookies from a
+ page and follow a location (and thus possibly send back cookies it received),
+ you can invoke it like:
- curl --cookie nada --location http://www.cookiesite.com
+ curl --cookie nada --location http://www.example.com
Curl has the ability to read and write cookie files that use the same file
format that Netscape and Mozilla do. It is a convenient way to share cookies
- between browsers and automatic scripts. The --cookie (-b) switch automatically
- detects if a given file is such a cookie file and parses it, and by using the
- --cookie-jar (-c) option you'll make curl write a new cookie file at the end of
- an operation:
+ between browsers and automatic scripts. The --cookie (-b) switch
+ automatically detects if a given file is such a cookie file and parses it,
+ and by using the --cookie-jar (-c) option you'll make curl write a new cookie
+ file at the end of an operation:
- curl --cookie cookies.txt --cookie-jar newcookies.txt http://www.cookiesite.com
+ curl --cookie cookies.txt --cookie-jar newcookies.txt \
+ http://www.example.com
11. HTTPS
Curl supports encrypted fetches thanks to the freely available OpenSSL
libraries. To get a page from a HTTPS server, simply run curl like:
- curl https://that.secure.server.com
+ curl https://secure.example.com
11.1 Certificates
can be specified on the command line or if not, entered interactively when
curl queries for it. Use a certificate with curl on a HTTPS server like:
- curl --cert mycert.pem https://that.secure.server.com
+ curl --cert mycert.pem https://secure.example.com
curl also tries to verify that the server is who it claims to be, by
verifying the server's certificate against a locally stored CA cert
For example, you can change the POST request to a PROPFIND and send the data
as "Content-Type: text/xml" (instead of the default Content-Type) like this:
- curl --data "<xml>" --header "Content-Type: text/xml" --request PROPFIND url.com
+ curl --data "<xml>" --header "Content-Type: text/xml" \
+ --request PROPFIND url.com
You can delete a default header by providing one without content. Like you
can ruin the request by chopping off the Host: header:
- curl --header "Host:" http://mysite.com
+ curl --header "Host:" http://www.example.com
You can add headers the same way. Your server may want a "Destination:"
header, and you can add it:
- curl --header "Destination: http://moo.com/nowhere" http://url.com
+ curl --header "Destination: http://nowhere" http://example.com
13. Web Login
to do a proper login POST. Remember that the contents need to be URL encoded
when sent in a normal POST.
-
14. Debug
Many times when you run curl on a site, you'll notice that the site doesn't
RFC 2616 is a must to read if you want in-depth understanding of the HTTP
protocol.
- RFC 2396 explains the URL syntax.
+ RFC 3986 explains the URL syntax.
RFC 2109 defines how cookies are supposed to work.
RFC 1867 defines the HTTP post upload format.
- http://www.openssl.org is the home of the OpenSSL project
-
http://curl.haxx.se is the home of the cURL project
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