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curl/README.curl
Daniel Stenberg e67157b5a2 Added some more explanatory text about HTTP posts
2000-03-27 21:42:40 +00:00

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LATEST VERSION
You always find news about what's going on as well as the latest versions
from the curl web pages, located at:
http://curl.haxx.nu
SIMPLE USAGE
Get the main page from netscape's web-server:
curl http://www.netscape.com/
Get the root README file from funet's ftp-server:
curl ftp://ftp.funet.fi/README
Get a gopher document from funet's gopher server:
curl gopher://gopher.funet.fi
Get a web page from a server using port 8000:
curl http://www.weirdserver.com:8000/
Get a list of the root directory of an FTP site:
curl ftp://ftp.fts.frontec.se/
Get the definition of curl from a dictionary:
curl dict://dict.org/m:curl
DOWNLOAD TO A FILE
Get a web page and store in a local file:
curl -o thatpage.html http://www.netscape.com/
Get a web page and store in a local file, make the local file get the name
of the remote document (if no file name part is specified in the URL, this
will fail):
curl -O http://www.netscape.com/index.html
USING PASSWORDS
FTP
To ftp files using name+passwd, include them in the URL like:
curl ftp://name:passwd@machine.domain:port/full/path/to/file
or specify them with the -u flag like
curl -u name:passwd ftp://machine.domain:port/full/path/to/file
HTTP
The HTTP URL doesn't support user and password in the URL string. Curl
does support that anyway to provide a ftp-style interface and thus you can
pick a file like:
curl http://name:passwd@machine.domain/full/path/to/file
or specify user and password separately like in
curl -u name:passwd http://machine.domain/full/path/to/file
NOTE! Since HTTP URLs don't support user and password, you can't use that
style when using Curl via a proxy. You _must_ use the -u style fetch
during such circumstances.
HTTPS
Probably most commonly used with private certificates, as explained below.
GOPHER
Curl features no password support for gopher.
PROXY
Get an ftp file using a proxy named my-proxy that uses port 888:
curl -x my-proxy:888 ftp://ftp.leachsite.com/README
Get a file from a HTTP server that requires user and password, using the
same proxy as above:
curl -u user:passwd -x my-proxy:888 http://www.get.this/
Some proxies require special authentication. Specify by using -U as above:
curl -U user:passwd -x my-proxy:888 http://www.get.this/
See also the environment variables Curl support that offer further proxy
control.
RANGES
With HTTP 1.1 byte-ranges were introduced. Using this, a client can request
to get only one or more subparts of a specified document. Curl supports
this with the -r flag.
Get the first 100 bytes of a document:
curl -r 0-99 http://www.get.this/
Get the last 500 bytes of a document:
curl -r -500 http://www.get.this/
Curl also supports simple ranges for FTP files as well. Then you can only
specify start and stop position.
Get the first 100 bytes of a document using FTP:
curl -r 0-99 ftp://www.get.this/README
UPLOADING
FTP
Upload all data on stdin to a specified ftp site:
curl -t ftp://ftp.upload.com/myfile
Upload data from a specified file, login with user and password:
curl -T uploadfile -u user:passwd ftp://ftp.upload.com/myfile
Upload a local file to the remote site, and use the local file name remote
too:
curl -T uploadfile -u user:passwd ftp://ftp.upload.com/
Upload a local file to get appended to the remote file using ftp:
curl -T localfile -a ftp://ftp.upload.com/remotefile
NOTE: Curl does not support ftp upload through a proxy! The reason for this
is simply that proxies are seldomly configured to allow this and that no
author has supplied code that makes it possible!
HTTP
Upload all data on stdin to a specified http site:
curl -t http://www.upload.com/myfile
Note that the http server must've been configured to accept PUT before this
can be done successfully.
For other ways to do http data upload, see the POST section below.
VERBOSE / DEBUG
If curl fails where it isn't supposed to, if the servers don't let you
in, if you can't understand the responses: use the -v flag to get VERBOSE
fetching. Curl will output lots of info and all data it sends and
receives in order to let the user see all client-server interaction.
curl -v ftp://ftp.upload.com/
DETAILED INFORMATION
Different protocols provide different ways of getting detailed information
about specific files/documents. To get curl to show detailed information
about a single file, you should use -I/--head option. It displays all
available info on a single file for HTTP and FTP. The HTTP information is a
lot more extensive.
For HTTP, you can get the header information (the same as -I would show)
shown before the data by using -i/--include. Curl understands the
-D/--dump-header option when getting files from both FTP and HTTP, and it
will then store the headers in the specified file.
Store the HTTP headers in a separate file:
curl --dump-header headers.txt curl.haxx.nu
Note that headers stored in a separate file can be very useful at a later
time if you want curl to use cookies sent by the server. More about that in
the cookies section.
POST (HTTP)
It's easy to post data using curl. This is done using the -d <data>
option. The post data must be urlencoded.
Post a simple "name" and "phone" guestbook.
curl -d "name=Rafael%20Sagula&phone=3320780" \
http://www.where.com/guest.cgi
How to post a form with curl, lesson #1:
Dig out all the <input> tags in the form that you want to fill in. (There's
a perl program called formfind.pl on the curl site that helps with this).
If there's a "normal" post, you use -d to post. -d takes a full "post
string", which is in the format
<variable1>=<data1>&<variable2>=<data2>&...
The 'variable' names are the names set with "name=" in the <input> tags, and
the data is the contents you want to fill in for the inputs. The data *must*
be properly URL encoded. That means you replace space with + and that you
write weird letters with %XX where XX is the hexadecimal representation of
the letter's ASCII code.
Example:
(page located at http://www.formpost.com/getthis/
<form action="post.cgi" method="post">
<input name=user size=10>
<input name=pass type=password size=10>
<input name=id type=hidden value="blablabla">
<input name=ding value="submit">
</form>
We want to enter user 'foobar' with password '12345'.
To post to this, you enter a curl command line like:
curl -d "user=foobar&pass=12345&id=blablabla&dig=submit" (continues)
http://www.formpost.com/getthis/post.cgi
While -d uses the application/x-www-form-urlencoded mime-type, generally
understood by CGI's and similar, curl also supports the more capable
multipart/form-data type. This latter type supports things like file upload.
-F accepts parameters like -F "name=contents". If you want the contents to
be read from a file, use <@filename> as contents. When specifying a file,
you can also specify which content type the file is, by appending
';type=<mime type>' to the file name. You can also post contents of several
files in one field. So that the field name 'coolfiles' can be sent three
files with different content types in a manner similar to:
curl -F "coolfiles=@fil1.gif;type=image/gif,fil2.txt,fil3.html" \
http://www.post.com/postit.cgi
If content-type is not specified, curl will try to guess from the extension
(it only knows a few), or use the previously specified type (from an earlier
file if several files are specified in a list) or finally using the default
type 'text/plain'.
Emulate a fill-in form with -F. Let's say you fill in three fields in a
form. One field is a file name which to post, one field is your name and one
field is a file description. We want to post the file we have written named
"cooltext.txt". To let curl do the posting of this data instead of your
favourite browser, you have to check out the HTML of the form page to get to
know the names of the input fields. In our example, the input field names are
'file', 'yourname' and 'filedescription'.
curl -F "file=@cooltext.txt" -F "yourname=Daniel" \
-F "filedescription=Cool text file with cool text inside" \
http://www.post.com/postit.cgi
So, to send two files in one post you can do it in two ways:
1. Send multiple files in a single "field" with a single field name:
curl -F "pictures=@dog.gif,cat.gif"
2. Send two fields with two field names:
curl -F "docpicture=@dog.gif" -F "catpicture=@cat.gif"
REFERER
A HTTP request has the option to include information about which address
that referred to actual page, and curl allows the user to specify that
referrer to get specified on the command line. It is especially useful to
fool or trick stupid servers or CGI scripts that rely on that information
being available or contain certain data.
curl -e www.coolsite.com http://www.showme.com/
USER AGENT
A HTTP request has the option to include information about the browser
that generated the request. Curl allows it to be specified on the command
line. It is especially useful to fool or trick stupid servers or CGI
scripts that only accept certain browsers.
Example:
curl -A 'Mozilla/3.0 (Win95; I)' http://www.nationsbank.com/
Other common strings:
'Mozilla/3.0 (Win95; I)' Netscape Version 3 for Windows 95
'Mozilla/3.04 (Win95; U)' Netscape Version 3 for Windows 95
'Mozilla/2.02 (OS/2; U)' Netscape Version 2 for OS/2
'Mozilla/4.04 [en] (X11; U; AIX 4.2; Nav)' NS for AIX
'Mozilla/4.05 [en] (X11; U; Linux 2.0.32 i586)' NS for Linux
Note that Internet Explorer tries hard to be compatible in every way:
'Mozilla/4.0 (compatible; MSIE 4.01; Windows 95)' MSIE for W95
Mozilla is not the only possible User-Agent name:
'Konqueror/1.0' KDE File Manager desktop client
'Lynx/2.7.1 libwww-FM/2.14' Lynx command line browser
COOKIES
Cookies are generally used by web servers to keep state information at the
client's side. The server sets cookies by sending a response line in the
headers that looks like 'Set-Cookie: <data>' where the data part then
typically contains a set of NAME=VALUE pairs (separated by semicolons ';'
like "NAME1=VALUE1; NAME2=VALUE2;"). The server can also specify for what
path the "cookie" should be used for (by specifying "path=value"), when the
cookie should expire ("expire=DATE"), for what domain to use it
("domain=NAME") and if it should be used on secure connections only
("secure").
If you've received a page from a server that contains a header like:
Set-Cookie: sessionid=boo123; path="/foo";
it means the server wants that first pair passed on when we get anything in
a path beginning with "/foo".
Example, get a page that wants my name passed in a cookie:
curl -b "name=Daniel" www.sillypage.com
Curl also has the ability to use previously received cookies in following
sessions. If you get cookies from a server and store them in a file in a
manner similar to:
curl --dump-header headers www.example.com
... you can then in a second connect to that (or another) site, use the
cookies from the 'headers' file like:
curl -b headers www.example.com
Note that by specifying -b you enable the "cookie awareness" and with -L
you can make curl follow a location: (which often is used in combination
with cookies). So that if a site sends cookies and a location, you can
use a non-existing file to trig the cookie awareness like:
curl -L -b empty-file www.example.com
The file to read cookies from must be formatted using plain HTTP headers OR
as netscape's cookie file. Curl will determine what kind it is based on the
file contents.
PROGRESS METER
The progress meter exists to show a user that something actually is
happening. The different fields in the output have the following meaning:
% Total % Received % Xferd Average Speed Time Curr.
Dload Upload Total Current Left Speed
0 151M 0 38608 0 0 9406 0 4:41:43 0:00:04 4:41:39 9287
From left-to-right:
% - percentage completed of the whole transfer
Total - total size of the whole expected transfer
% - percentage completed of the download
Received - currently downloaded amount of bytes
% - percentage completed of the upload
Xferd - currently uploaded amount of bytes
Average Speed
Dload - the average transfer speed of the download
Average Speed
Upload - the average transfer speed of the upload
Time Total - expected time to complete the operation
Time Current - time passed since the invoke
Time Left - expected time left to completetion
Curr.Speed - the average transfer speed the last 5 seconds (the first
5 seconds of a transfer is based on less time of course.)
The -# option will display a totally different progress bar that doesn't
need much explanation!
SPEED LIMIT
Curl offers the user to set conditions regarding transfer speed that must
be met to let the transfer keep going. By using the switch -y and -Y you
can make curl abort transfers if the transfer speed doesn't exceed your
given lowest limit for a specified time.
To let curl abandon downloading this page if its slower than 3000 bytes per
second for 1 minute, run:
curl -y 3000 -Y 60 www.far-away-site.com
This can very well be used in combination with the overall time limit, so
that the above operatioin must be completed in whole within 30 minutes:
curl -m 1800 -y 3000 -Y 60 www.far-away-site.com
CONFIG FILE
Curl automatically tries to read the .curlrc file (or _curlrc file on win32
systems) from the user's home dir on startup. The config file should be
made up with normal command line switches. Comments can be used within the
file. If the first letter on a line is a '#'-letter the rest of the line
is treated as a comment.
Example, set default time out and proxy in a config file:
# We want a 30 minute timeout:
-m 1800
# ... and we use a proxy for all accesses:
-x proxy.our.domain.com:8080
White spaces ARE significant at the end of lines, but all white spaces
leading up to the first characters of each line are ignored.
Prevent curl from reading the default file by using -q as the first command
line parameter, like:
curl -q www.thatsite.com
Force curl to get and display a local help page in case it is invoked
without URL by making a config file similar to:
# default url to get
http://help.with.curl.com/curlhelp.html
You can specify another config file to be read by using the -K/--config
flag. If you set config file name to "-" it'll read the config from stdin,
which can be handy if you want to hide options from being visible in process
tables etc:
echo "-u user:passwd" | curl -K - http://that.secret.site.com
EXTRA HEADERS
When using curl in your own very special programs, you may end up needing
to pass on your own custom headers when getting a web page. You can do
this by using the -H flag.
Example, send the header "X-you-and-me: yes" to the server when getting a
page:
curl -H "X-you-and-me: yes" www.love.com
This can also be useful in case you want curl to send a different text in
a header than it normally does. The -H header you specify then replaces the
header curl would normally send.
FTP and PATH NAMES
Do note that when getting files with the ftp:// URL, the given path is
relative the directory you enter. To get the file 'README' from your home
directory at your ftp site, do:
curl ftp://user:passwd@my.site.com/README
But if you want the README file from the root directory of that very same
site, you need to specify the absolute file name:
curl ftp://user:passwd@my.site.com//README
(I.e with an extra slash in front of the file name.)
FTP and firewalls
The FTP protocol requires one of the involved parties to open a second
connction as soon as data is about to get transfered. There are two ways to
do this.
The default way for curl is to issue the PASV command which causes the
server to open another port and await another connection performed by the
client. This is good if the client is behind a firewall that don't allow
incoming connections.
curl ftp.download.com
If the server for example, is behind a firewall that don't allow connections
on other ports than 21 (or if it just doesn't support the PASV command), the
other way to do it is to use the PORT command and instruct the server to
connect to the client on the given (as parameters to the PORT command) IP
number and port.
The -P flag to curl allows for different options. Your machine may have
several IP-addresses and/or network interfaces and curl allows you to select
which of them to use. Default address can also be used:
curl -P - ftp.download.com
Download with PORT but use the IP address of our 'le0' interface:
curl -P le0 ftp.download.com
Download with PORT but use 192.168.0.10 as our IP address to use:
curl -P 192.168.0.10 ftp.download.com
HTTPS
Secure HTTP requires SSL libraries to be installed and used when curl is
built. If that is done, curl is capable of retrieving and posting documents
using the HTTPS procotol.
Example:
curl https://www.secure-site.com
Curl is also capable of using your personal certificates to get/post files
from sites that require valid certificates. The only drawback is that the
certificate needs to be in PEM-format. PEM is a standard and open format to
store certificates with, but it is not used by the most commonly used
browsers (Netscape and MSEI both use the so called PKCS#12 format). If you
want curl to use the certificates you use with your (favourite) browser, you
may need to download/compile a converter that can convert your browser's
formatted certificates to PEM formatted ones. This kind of converter is
included in recent versions of OpenSSL, and for older versions Dr Stephen
N. Henson has written a patch for SSLeay that adds this functionality. You
can get his patch (that requires an SSLeay installation) from his site at:
http://www.drh-consultancy.demon.co.uk/
Example on how to automatically retrieve a document using a certificate with
a personal password:
curl -E /path/to/cert.pem:password https://secure.site.com/
If you neglect to specify the password on the command line, you will be
prompted for the correct password before any data can be received.
Many older SSL-servers have problems with SSLv3 or TLS, that newer versions
of OpenSSL etc is using, therefore it is sometimes useful to specify what
SSL-version curl should use. Use -3 or -2 to specify that exact SSL version
to use:
curl -2 https://secure.site.com/
Otherwise, curl will first attempt to use v3 and then v2.
RESUMING FILE TRANSFERS
To continue a file transfer where it was previously aborted, curl supports
resume on http(s) downloads as well as ftp uploads and downloads.
Continue downloading a document:
curl -c -o file ftp://ftp.server.com/path/file
Continue uploading a document(*1):
curl -c -T file ftp://ftp.server.com/path/file
Continue downloading a document from a web server(*2):
curl -c -o file http://www.server.com/
(*1) = This requires that the ftp server supports the non-standard command
SIZE. If it doesn't, curl will say so.
(*2) = This requires that the wb server supports at least HTTP/1.1. If it
doesn't, curl will say so.
TIME CONDITIONS
HTTP allows a client to specify a time condition for the document it
requests. It is If-Modified-Since or If-Unmodified-Since. Curl allow you to
specify them with the -z/--time-cond flag.
For example, you can easily make a download that only gets performed if the
remote file is newer than a local copy. It would be made like:
curl -z local.html http://remote.server.com/remote.html
Or you can download a file only if the local file is newer than the remote
one. Do this by prepending the date string with a '-', as in:
curl -z -local.html http://remote.server.com/remote.html
You can specify a "free text" date as condition. Tell curl to only download
the file if it was updated since yesterday:
curl -z yesterday http://remote.server.com/remote.html
Curl will then accept a wide range of date formats. You always make the date
check the other way around by prepending it with a dash '-'.
DICT
For fun try
curl dict://dict.org/m:curl
curl dict://dict.org/d:heisenbug:jargon
curl dict://dict.org/d:daniel:web1913
Aliases for 'm' are 'match' and 'find', and aliases for 'd' are 'define'
and 'lookup'. For example,
curl dict://dict.org/find:curl
Commands that break the URL description of the RFC (but not the DICT
protocol) are
curl dict://dict.org/show:db
curl dict://dict.org/show:strat
Authentication is still missing (but this is not required by the RFC)
LDAP
If you have installed the OpenLDAP library, curl can take advantage of it
and offer ldap:// support.
LDAP is a complex thing and writing an LDAP query is not an easy task. I do
advice you to dig up the syntax description for that elsewhere, RFC 1959 if
no other place is better.
To show you an example, this is now I can get all people from my local LDAP
server that has a certain sub-domain in their email address:
curl -B "ldap://ldap.frontec.se/o=frontec??sub?mail=*sth.frontec.se"
If I want the same info in HTML format, I can get it by not using the -B
(enforce ASCII) flag.
ENVIRONMENT VARIABLES
Curl reads and understands the following environment variables:
HTTP_PROXY, HTTPS_PROXY, FTP_PROXY, GOPHER_PROXY
They should be set for protocol-specific proxies. General proxy should be
set with
ALL_PROXY
A comma-separated list of host names that shouldn't go through any proxy is
set in (only an asterisk, '*' matches all hosts)
NO_PROXY
If a tail substring of the domain-path for a host matches one of these
strings, transactions with that node will not be proxied.
The usage of the -x/--proxy flag overrides the environment variables.
NETRC
Unix introduced the .netrc concept a long time ago. It is a way for a user
to specify name and password for commonly visited ftp sites in a file so
that you don't have to type them in each time you visit those sites. You
realize this is a big security risk if someone else gets hold of your
passwords, so therefor most unix programs won't read this file unless it is
only readable by yourself (curl doesn't care though).
Curl supports .netrc files if told so (using the -n/--netrc option). This is
not restricted to only ftp, but curl can use it for all protocols where
authentication is used.
A very simple .netrc file could look something like:
machine curl.haxx.nu login iamdaniel password mysecret
CUSTOM OUTPUT
To better allow script programmers to get to know about the progress of
curl, the -w/--write-out option was introduced. Using this, you can specify
what information from the previous transfer you want to extract.
To display the amount of bytes downloaded together with some text and an
ending newline:
curl -w 'We downloaded %{size_download} bytes\n' www.download.com
MAILING LIST
We have an open mailing list to discuss curl, its development and things
relevant to this.
To subscribe, mail curl-request@contactor.se with "subscribe <your email
address>" in the body.
To post to the list, mail curl@contactor.se.
To unsubcribe, mail curl-request@contactor.se with "unsubscribe <your
subscribed email address>" in the body.
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