libcurl: updated to 7.49.1

[tomato.git] / release / src / router / libcurl / docs / MANUAL

LATEST VERSION

  You always find news about what's going on as well as the latest versions
  from the curl web pages, located at:

        https://curl.haxx.se

SIMPLE USAGE

  Get the main page from Netscape's web-server:

        curl http://www.netscape.com/

  Get the README file the user's home directory at funet's ftp-server:

        curl ftp://ftp.funet.fi/README

  Get a web page from a server using port 8000:

        curl http://www.weirdserver.com:8000/

  Get a directory listing of an FTP site:

        curl ftp://cool.haxx.se/

  Get the definition of curl from a dictionary:

        curl dict://dict.org/m:curl

  Fetch two documents at once:

        curl ftp://cool.haxx.se/ http://www.weirdserver.com:8000/

  Get a file off an FTPS server:

        curl ftps://files.are.secure.com/secrets.txt

  or use the more appropriate FTPS way to get the same file:

        curl --ftp-ssl ftp://files.are.secure.com/secrets.txt

  Get a file from an SSH server using SFTP:

        curl -u username sftp://example.com/etc/issue

  Get a file from an SSH server using SCP using a private key
  (not password-protected) to authenticate:

        curl -u username: --key ~/.ssh/id_rsa \
             scp://example.com/~/file.txt

  Get a file from an SSH server using SCP using a private key
  (password-protected) to authenticate:

        curl -u username: --key ~/.ssh/id_rsa --pass private_key_password \
             scp://example.com/~/file.txt

  Get the main page from an IPv6 web server:

        curl "http://[2001:1890:1112:1::20]/"

  Get a file from an SMB server:

        curl -u "domain\username:passwd" smb://server.example.com/share/file.txt

DOWNLOAD TO A FILE

  Get a web page and store in a local file with a specific name:

        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

  Fetch two files and store them with their remote names:

        curl -O www.haxx.se/index.html -O curl.haxx.se/download.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

 FTPS

   It is just like for FTP, but you may also want to specify and use
   SSL-specific options for certificates etc.

   Note that using FTPS:// as prefix is the "implicit" way as described in the
   standards while the recommended "explicit" way is done by using FTP:// and
   the --ftp-ssl option.

 SFTP / SCP

   This is similar to FTP, but you can use the --key option to specify a
   private key to use instead of a password. Note that the private key may
   itself be protected by a password that is unrelated to the login password
   of the remote system; this password is specified using the --pass option.
   Typically, curl will automatically extract the public key from the private
   key file, but in cases where curl does not have the proper library support,
   a matching public key file must be specified using the --pubkey option.

 HTTP

   Curl also supports user and password in HTTP URLs, 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

   HTTP offers many different methods of authentication and curl supports
   several: Basic, Digest, NTLM and Negotiate (SPNEGO). Without telling which
   method to use, curl defaults to Basic. You can also ask curl to pick the
   most secure ones out of the ones that the server accepts for the given URL,
   by using --anyauth.

   NOTE! According to the URL specification, HTTP URLs can not contain a user
   and password, so that style will not work when using curl via a proxy, even
   though curl allows it at other times. When using a proxy, you _must_ use
   the -u style for user and password.

 HTTPS

   Probably most commonly used with private certificates, as explained below.

PROXY

 curl supports both HTTP and SOCKS proxy servers, with optional authentication.
 It does not have special support for FTP proxy servers since there are no
 standards for those, but it can still be made to work with many of them. You
 can also use both HTTP and SOCKS proxies to transfer files to and from FTP
 servers.

 Get an ftp file using an HTTP proxy named my-proxy that uses port 888:

        curl -x my-proxy:888 ftp://ftp.leachsite.com/README

 Get a file from an 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/

 A comma-separated list of hosts and domains which do not use the proxy can
 be specified as:

        curl --noproxy localhost,get.this -x my-proxy:888 http://www.get.this/

 If the proxy is specified with --proxy1.0 instead of --proxy or -x, then
 curl will use HTTP/1.0 instead of HTTP/1.1 for any CONNECT attempts.

 curl also supports SOCKS4 and SOCKS5 proxies with --socks4 and --socks5.

 See also the environment variables Curl supports that offer further proxy
 control.

 Most FTP proxy servers are set up to appear as a normal FTP server from the
 client's perspective, with special commands to select the remote FTP server.
 curl supports the -u, -Q and --ftp-account options that can be used to
 set up transfers through many FTP proxies. For example, a file can be
 uploaded to a remote FTP server using a Blue Coat FTP proxy with the
 options:

   curl -u "Remote-FTP-Username@remote.ftp.server Proxy-Username:Remote-Pass" \
    --ftp-account Proxy-Password --upload-file local-file \
    ftp://my-ftp.proxy.server:21/remote/upload/path/

 See the manual for your FTP proxy to determine the form it expects to set up
 transfers, and curl's -v option to see exactly what curl is sending.

RANGES

  HTTP 1.1 introduced byte-ranges. 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 / FTPS / SFTP / SCP

  Upload all data on stdin to a specified server:

        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 at the remote
  site too:

        curl -T uploadfile -u user:passwd ftp://ftp.upload.com/

  Upload a local file to get appended to the remote file:

        curl -T localfile -a ftp://ftp.upload.com/remotefile

  Curl also supports ftp upload through a proxy, but only if the proxy is
  configured to allow that kind of tunneling. If it does, you can run curl in
  a fashion similar to:

        curl --proxytunnel -x proxy:port -T localfile ftp.upload.com

SMB / SMBS

        curl -T file.txt -u "domain\username:passwd" 
         smb://server.example.com/share/

 HTTP

  Upload all data on stdin to a specified HTTP site:

        curl -T - http://www.upload.com/myfile

  Note that the HTTP server must have 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 what it sends and receives in
  order to let the user see all client-server interaction (but it won't show
  you the actual data).

        curl -v ftp://ftp.upload.com/

  To get even more details and information on what curl does, try using the
  --trace or --trace-ascii options with a given file name to log to, like
  this:

        curl --trace trace.txt www.haxx.se


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 (headers.txt in the example):

        curl --dump-header headers.txt curl.haxx.se

  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
  replace 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&ding=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 the file content type by appending ';type=<mime type>'
  to the file name. You can also post the contents of several files in one
  field.  For example, the field name 'coolfiles' is used to send three files,
  with different content types using the following syntax:

        curl -F "coolfiles=@fil1.gif;type=image/gif,fil2.txt,fil3.html" \
        http://www.post.com/postit.cgi

  If the content-type is not specified, curl will try to guess from the file
  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 else it will
  use the default type 'application/octet-stream'.

  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 read the HTML source of the form page and
  find 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

  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"

  To send a field value literally without interpreting a leading '@'
  or '<', or an embedded ';type=', use --form-string instead of
  -F. This is recommended when the value is obtained from a user or
  some other unpredictable source. Under these circumstances, using
  -F instead of --form-string would allow a user to trick curl into
  uploading a file.

REFERRER

  An HTTP request has the option to include information about which address
  referred it to the actual page.  Curl allows you to specify the
  referrer to be used 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/

  NOTE: The Referer: [sic] field is defined in the HTTP spec to be a full URL.

USER AGENT

  An 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

  While saving headers to a file is a working way to store cookies, it is
  however error-prone and not the preferred way to do this. Instead, make curl
  save the incoming cookies using the well-known netscape cookie format like
  this:

        curl -c cookies.txt 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 trigger the cookie awareness like:

        curl -L -b empty.txt 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.  In the above command, curl will parse the header and store
  the cookies received from www.example.com.  curl will send to the server the
  stored cookies which match the request as it follows the location.  The
  file "empty.txt" may be a nonexistent file.

  To read and write cookies from a netscape cookie file, you can set both -b
  and -c to use the same file:

        curl -b cookies.txt -c cookies.txt www.example.com

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 completion
   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 allows the user to set the transfer speed conditions 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 is below the specified
  lowest limit for a specified time.

  To have curl abort the download if the speed is 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 operation must be completed in whole within 30 minutes:

        curl -m 1800 -Y 3000 -y 60 www.far-away-site.com

  Forcing curl not to transfer data faster than a given rate is also possible,
  which might be useful if you're using a limited bandwidth connection and you
  don't want your transfer to use all of it (sometimes referred to as
  "bandwidth throttle").

  Make curl transfer data no faster than 10 kilobytes per second:

        curl --limit-rate 10K www.far-away-site.com

    or

        curl --limit-rate 10240 www.far-away-site.com

  Or prevent curl from uploading data faster than 1 megabyte per second:

        curl -T upload --limit-rate 1M ftp://uploadshereplease.com

  When using the --limit-rate option, the transfer rate is regulated on a
  per-second basis, which will cause the total transfer speed to become lower
  than the given number. Sometimes of course substantially lower, if your
  transfer stalls during periods.

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 could be made up with normal command line switches, but you
  can also specify the long options without the dashes to make it more
  readable. You can separate the options and the parameter with spaces, or
  with = or :. Comments can be used within the file. If the first letter on a
  line is a '#'-symbol the rest of the line is treated as a comment.

  If you want the parameter to contain spaces, you must enclose the entire
  parameter within double quotes ("). Within those quotes, you specify a
  quote as \".

  NOTE: You must specify options and their arguments on the same line.

  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:
        proxy = 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
        url = "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 "user = 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. If you replace an internal header with an
  empty one, you prevent that header from being sent. To prevent the Host:
  header from being used:

        curl -H "Host:" www.server.com

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.)

SFTP and SCP and PATH NAMES

  With sftp: and scp: URLs, the path name given is the absolute name on the
  server. To access a file relative to the remote user's home directory,
  prefix the file with /~/ , such as:

        curl -u $USER sftp://home.example.com/~/.bashrc

FTP and firewalls

  The FTP protocol requires one of the involved parties to open a second
  connection as soon as data is about to get transferred. 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 doesn't allow
  incoming connections.

        curl ftp.download.com

  If the server, for example, is behind a firewall that doesn't allow connections
  on ports other 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 IP number and port (as parameters to the
  PORT command).

  The -P flag to curl supports a few 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 (this does
  not work on windows):

        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

NETWORK INTERFACE

  Get a web page from a server using a specified port for the interface:

        curl --interface eth0:1 http://www.netscape.com/

  or

        curl --interface 192.168.1.10 http://www.netscape.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 protocol.

  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 MSIE 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, which newer versions
  of OpenSSL etc use, therefore it is sometimes useful to specify what
  SSL-version curl should use. Use -3, -2 or -1 to specify that exact SSL
  version to use (for SSLv3, SSLv2 or TLSv1 respectively):

        curl -2 https://secure.site.com/

  Otherwise, curl will first attempt to use v3 and then v2.

  To use OpenSSL to convert your favourite browser's certificate into a PEM
  formatted one that curl can use, do something like this:

    In Netscape, you start with hitting the 'Security' menu button.

    Select 'certificates->yours' and then pick a certificate in the list

    Press the 'Export' button

    enter your PIN code for the certs

    select a proper place to save it

    Run the 'openssl' application to convert the certificate. If you cd to the
    openssl installation, you can do it like:

     # ./apps/openssl pkcs12 -in [file you saved] -clcerts -out [PEMfile]

    In Firefox, select Options, then Advanced, then the Encryption tab,
    View Certificates. This opens the Certificate Manager, where you can
    Export. Be sure to select PEM for the Save as type.

    In Internet Explorer, select Internet Options, then the Content tab, then
    Certificates. Then you can Export, and depending on the format you may
    need to convert to PEM.

    In Chrome, select Settings, then Show Advanced Settings. Under HTTPS/SSL
    select Manage Certificates.

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 web 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 allows 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 January 12, 2012:

        curl -z "Jan 12 2012" 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
  advise you to dig up the syntax description for that elsewhere. Two places
  that might suit you are:

  Netscape's "Netscape Directory SDK 3.0 for C Programmer's Guide Chapter 10:
  Working with LDAP URLs":
  http://developer.netscape.com/docs/manuals/dirsdk/csdk30/url.htm

  RFC 2255, "The LDAP URL Format" https://curl.haxx.se/rfc/rfc2255.txt

  To show you an example, this is how 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

  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 the host name matches one of these strings, or the host is within the
  domain of 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 therefore 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 to (using the -n/--netrc and
  --netrc-optional options). This is not restricted to just FTP,
  so curl can use it for all protocols where authentication is used.

  A very simple .netrc file could look something like:

        machine curl.haxx.se 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

KERBEROS FTP TRANSFER

  Curl supports kerberos4 and kerberos5/GSSAPI for FTP transfers. You need
  the kerberos package installed and used at curl build time for it to be
  available.

  First, get the krb-ticket the normal way, like with the kinit/kauth tool.
  Then use curl in way similar to:

        curl --krb private ftp://krb4site.com -u username:fakepwd

  There's no use for a password on the -u switch, but a blank one will make
  curl ask for one and you already entered the real password to kinit/kauth.

TELNET

  The curl telnet support is basic and very easy to use. Curl passes all data
  passed to it on stdin to the remote server. Connect to a remote telnet
  server using a command line similar to:

        curl telnet://remote.server.com

  And enter the data to pass to the server on stdin. The result will be sent
  to stdout or to the file you specify with -o.

  You might want the -N/--no-buffer option to switch off the buffered output
  for slow connections or similar.

  Pass options to the telnet protocol negotiation, by using the -t option. To
  tell the server we use a vt100 terminal, try something like:

        curl -tTTYPE=vt100 telnet://remote.server.com

  Other interesting options for it -t include:

   - XDISPLOC=<X display> Sets the X display location.

   - NEW_ENV=<var,val> Sets an environment variable.

  NOTE: The telnet protocol does not specify any way to login with a specified
  user and password so curl can't do that automatically. To do that, you need
  to track when the login prompt is received and send the username and
  password accordingly.

PERSISTENT CONNECTIONS

  Specifying multiple files on a single command line will make curl transfer
  all of them, one after the other in the specified order.

  libcurl will attempt to use persistent connections for the transfers so that
  the second transfer to the same host can use the same connection that was
  already initiated and was left open in the previous transfer. This greatly
  decreases connection time for all but the first transfer and it makes a far
  better use of the network.

  Note that curl cannot use persistent connections for transfers that are used
  in subsequence curl invokes. Try to stuff as many URLs as possible on the
  same command line if they are using the same host, as that'll make the
  transfers faster. If you use an HTTP proxy for file transfers, practically
  all transfers will be persistent.

MULTIPLE TRANSFERS WITH A SINGLE COMMAND LINE

  As is mentioned above, you can download multiple files with one command line
  by simply adding more URLs. If you want those to get saved to a local file
  instead of just printed to stdout, you need to add one save option for each
  URL you specify. Note that this also goes for the -O option (but not
  --remote-name-all).

  For example: get two files and use -O for the first and a custom file
  name for the second:

    curl -O http://url.com/file.txt ftp://ftp.com/moo.exe -o moo.jpg

  You can also upload multiple files in a similar fashion:

    curl -T local1 ftp://ftp.com/moo.exe -T local2 ftp://ftp.com/moo2.txt

IPv6

  curl will connect to a server with IPv6 when a host lookup returns an IPv6
  address and fall back to IPv4 if the connection fails. The --ipv4 and --ipv6
  options can specify which address to use when both are available. IPv6
  addresses can also be specified directly in URLs using the syntax:

    http://[2001:1890:1112:1::20]/overview.html

  When this style is used, the -g option must be given to stop curl from
  interpreting the square brackets as special globbing characters.  Link local
  and site local addresses including a scope identifier, such as fe80::1234%1,
  may also be used, but the scope portion must be numeric or match an existing
  network interface on Linux and the percent character must be URL escaped. The
  previous example in an SFTP URL might look like:

    sftp://[fe80::1234%251]/

  IPv6 addresses provided other than in URLs (e.g. to the --proxy, --interface
  or --ftp-port options) should not be URL encoded.

METALINK

  Curl supports Metalink (both version 3 and 4 (RFC 5854) are supported), a way
  to list multiple URIs and hashes for a file. Curl will make use of the mirrors
  listed within for failover if there are errors (such as the file or server not
  being available). It will also verify the hash of the file after the download
  completes. The Metalink file itself is downloaded and processed in memory and
  not stored in the local file system.

  Example to use a remote Metalink file:

    curl --metalink http://www.example.com/example.metalink

  To use a Metalink file in the local file system, use FILE protocol (file://):

    curl --metalink file://example.metalink

  Please note that if FILE protocol is disabled, there is no way to use a local
  Metalink file at the time of this writing. Also note that if --metalink and
  --include are used together, --include will be ignored. This is because including
  headers in the response will break Metalink parser and if the headers are included
  in the file described in Metalink file, hash check will fail.

MAILING LISTS

  For your convenience, we have several open mailing lists to discuss curl,
  its development and things relevant to this. Get all info at
  https://curl.haxx.se/mail/. Some of the lists available are:

  curl-users

    Users of the command line tool. How to use it, what doesn't work, new
    features, related tools, questions, news, installations, compilations,
    running, porting etc.

  curl-library

    Developers using or developing libcurl. Bugs, extensions, improvements.

  curl-announce

    Low-traffic. Only receives announcements of new public versions. At worst,
    that makes something like one or two mails per month, but usually only one
    mail every second month.

  curl-and-php

    Using the curl functions in PHP. Everything curl with a PHP angle. Or PHP
    with a curl angle.

  curl-and-python

    Python hackers using curl with or without the python binding pycurl.

  Please direct curl questions, feature requests and trouble reports to one of
  these mailing lists instead of mailing any individual.