curl tutorial
Simple Usage
Get the main page from a web-server:
curl https://www.example.com/
Get a README file from an FTP server:
curl ftp://ftp.example.com/README
Get a webpage from a server using port 8000:
curl http://www.example.com:8000/
Get a directory listing of an FTP site:
curl ftp://ftp.example.com/
Get the all terms matching curl from a dictionary:
curl dict://dict.example.com/m:curl
Get the definition of curl from a dictionary:
curl dict://dict.example.com/d:curl
Fetch two documents at once:
curl ftp://ftp.example.com/ http://www.example.com:8000/
Get a file off an FTPS server:
curl ftps://files.are.example.com/secrets.txt
or use the more appropriate FTPS way to get the same file:
curl --ssl-reqd ftp://files.are.example.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 webpage and store in a local file with a specific name:
curl -o thatpage.html http://www.example.com/
Get a webpage and store in a local file, make the local file get the name of the remote document (if no filename part is specified in the URL, this fails):
curl -O http://www.example.com/index.html
Fetch two files and store them with their remote names:
curl -O www.haxx.se/index.html -O curl.se/download.html
Using Passwords
FTP
To ftp files using name and password, include them in the URL like:
curl ftp://name:passwd@ftp.server.example:port/full/path/to/file
or specify them with the -u
flag like
curl -u name:passwd ftp://ftp.server.example: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 --ssl-reqd
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 automatically
extracts 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@http.server.example/full/path/to/file
or specify user and password separately like in
curl -u name:passwd http://http.server.example/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 does 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.example.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.example.com/
Some proxies require special authentication. Specify by using -U as above:
curl -U user:passwd -x my-proxy:888 http://www.example.com/
A comma-separated list of hosts and domains which do not use the proxy can be specified as:
curl --noproxy example.com -x my-proxy:888 http://www.example.com/
If the proxy is specified with --proxy1.0
instead of
--proxy
or -x
, then curl uses 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 "username@ftp.server.example Proxy-Username:Remote-Pass"
--ftp-account Proxy-Password --upload-file local-file
ftp://my-ftp.proxy.example: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.
Piping
Get a key file and add it with apt-key
(when on a system
that uses apt
for package management):
curl -L https://apt.example.org/llvm-snapshot.gpg.key | sudo apt-key add -
The '|' pipes the output to STDIN. -
tells
apt-key
that the key file should be read from STDIN.
Ranges
HTTP 1.1 introduced byte-ranges. Using this, a client can request to
get only one or more sub-parts 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.example.com/
Get the last 500 bytes of a document:
curl -r -500 http://www.example.com/
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.example.com/README
Uploading
FTP / FTPS / SFTP / SCP
Upload all data on stdin to a specified server:
curl -T - ftp://ftp.example.com/myfile
Upload data from a specified file, login with user and password:
curl -T uploadfile -u user:passwd ftp://ftp.example.com/myfile
Upload a local file to the remote site, and use the local filename at the remote site too:
curl -T uploadfile -u user:passwd ftp://ftp.example.com/
Upload a local file to get appended to the remote file:
curl -T localfile -a ftp://ftp.example.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.example.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.example.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 is not supposed to, if the servers do not let
you in, if you cannot understand the responses: use the -v
flag to get verbose fetching. Curl outputs lots of info and what it
sends and receives in order to let the user see all client-server
interaction (but it does not show you the actual data).
curl -v ftp://ftp.example.com/
To get even more details and information on what curl does, try using
the --trace
or --trace-ascii
options with a
given filename to log to, like this:
curl --trace my-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 then stores 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.se
Note that headers stored in a separate file can be 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 is 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.example.com/guest.cgi
Or automatically URL encode the data.
curl --data-urlencode "name=Rafael Sagula&phone=3320780"
http://www.example.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.
If there is 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:
(say if http://example.com
had the following html)
<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 would enter a curl command line like:
curl -d "user=foobar&pass=12345&id=blablabla&ding=submit"
http://example.com/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 filename. 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.example.com/postit.cgi
If the content-type is not specified, curl tries 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 uses 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 filename 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 favorite 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.example.com/postit.cgi
To send two files in one post you can do it in two ways:
Send multiple files in a single field with a single field name:
curl -F "pictures=@dog.gif,cat.gif" $URL
Send two fields with two field names
curl -F "docpicture=@dog.gif" -F "catpicture=@cat.gif" $URL
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
could 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.example.org http://www.example.com/
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.bank.example.com/
Other common strings:
Mozilla/3.0 (Win95; I)
- Netscape Version 3 for Windows 95Mozilla/3.04 (Win95; U)
- Netscape Version 3 for Windows 95Mozilla/2.02 (OS/2; U)
- Netscape Version 2 for OS/2Mozilla/4.04 [en] (X11; U; AIX 4.2; Nav)
- Netscape for AIXMozilla/4.05 [en] (X11; U; Linux 2.0.32 i586)
- Netscape 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 clientLynx/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 have 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.example.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.txt
file like:
curl -b headers.txt 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 engine
and with -L
you can make curl follow a
location:
(which often is used in combination with
cookies). If a site sends cookies and a location field, 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 determines what kind it is
based on the file contents. In the above command, curl parses the header
and store the cookies received from www.example.com. curl sends the stored
cookies which match the request to the server 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 transferTotal
- total size of the whole expected transfer%
- percentage completed of the downloadReceived
- currently downloaded amount of bytes%
- percentage completed of the uploadXferd
- currently uploaded amount of bytesAverage Speed Dload
- the average transfer speed of the downloadAverage Speed Upload
- the average transfer speed of the uploadTime Total
- expected time to complete the operationTime Current
- time passed since the invokeTime Left
- expected time left to completionCurr.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 displays a totally different progress bar
that does not 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.example.com
This can 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.example.com
Forcing curl not to transfer data faster than a given rate is also possible, which might be useful if you are using a limited bandwidth connection and you do not 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.example.com
or
curl --limit-rate 10240 www.far-away.example.com
Or prevent curl from uploading data faster than 1 megabyte per second:
curl -T upload --limit-rate 1M ftp://uploads.example.com
When using the --limit-rate
option, the transfer rate is
regulated on a per-second basis, which causes 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 Microsoft Windows systems) from the user's
home directory 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
Whitespaces ARE significant at the end of lines, but all whitespace 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.example.org
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.example.com/curlhelp.html"
You can specify another config file to be read by using the
-K
/--config
flag. If you set config filename
to -
it reads 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.example.com
Extra Headers
When using curl in your own programs, you may end up needing to pass
on your own custom headers when getting a webpage. 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" love.example.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:" server.example.com
FTP and Path Names
Do note that when getting files with a ftp://
URL, the
given path is relative to the directory you enter. To get the file
README
from your home directory at your ftp site, do:
curl ftp://user:passwd@my.example.com/README
If you want the README file from the root directory of that same site, you need to specify the absolute filename:
curl ftp://user:passwd@my.example.com//README
(I.e with an extra slash in front of the filename.)
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 does not allow incoming connections.
curl ftp.example.com
If the server, for example, is behind a firewall that does not allow
connections on ports other than 21 (or if it just does not 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.example.com
Download with PORT
but use the IP address of our
le0
interface (this does not work on Windows):
curl -P le0 ftp.example.com
Download with PORT
but use 192.168.0.10 as our IP
address to use:
curl -P 192.168.0.10 ftp.example.com
Network Interface
Get a webpage from a server using a specified port for the interface:
curl --interface eth0:1 http://www.example.com/
or
curl --interface 192.168.1.10 http://www.example.com/
HTTPS
Secure HTTP requires a TLS library 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://secure.example.com
curl is also capable of using client 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. If you want curl to use the certificates you use with your favorite browser, you may need to download/compile a converter that can convert your browser's formatted certificates to PEM formatted ones.
Example on how to automatically retrieve a document using a certificate with a personal password:
curl -E /path/to/cert.pem:password https://secure.example.com/
If you neglect to specify the password on the command line, you are prompted for the correct password before any data can be received.
Many older HTTPS servers have problems with specific SSL or TLS versions, which newer versions of OpenSSL etc use, therefore it is sometimes useful to specify what TLS version curl should use.:
curl --tlv1.0 https://secure.example.com/
Otherwise, curl attempts to use a sensible TLS default version.
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.example.com/path/file
Continue uploading a document:
curl -C - -T file ftp://ftp.example.com/path/file
Continue downloading a document from a web server
curl -C - -o file http://www.example.com/
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.example.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.example.com/remote.html
You can specify a plain 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.example.com/remote.html
curl accepts 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:gcide
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 support is still missing
LDAP
If you have installed the OpenLDAP library, curl can take advantage
of it and offer ldap://
support. On Windows, curl uses
WinLDAP from Platform SDK by default.
Default protocol version used by curl is LDAP version 3. Version 2 is used as a fallback mechanism in case version 3 fails to connect.
LDAP is a complex thing and writing an LDAP query is not an easy task. Familiarize yourself with the exact syntax description elsewhere. One such place might be: RFC 2255, The LDAP URL Format
To show you an example, this is how to get all people from an LDAP server that has a certain subdomain in their email address:
curl -B "ldap://ldap.example.com/o=frontec??sub?mail=*sth.example.com"
You also can use authentication when accessing LDAP catalog:
curl -u user:passwd "ldap://ldap.example.com/o=frontec??sub?mail=*"
curl "ldap://user:passwd@ldap.example.com/o=frontec??sub?mail=*"
By default, if user and password are provided, OpenLDAP/WinLDAP uses
basic authentication. On Windows you can control this behavior by
providing one of --basic
, --ntlm
or
--digest
option in curl command line
curl --ntlm "ldap://user:passwd@ldap.example.com/o=frontec??sub?mail=*"
On Windows, if no user/password specified, auto-negotiation mechanism is used with current logon credentials (SSPI/SPNEGO).
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 hostnames that should not go through any
proxy is set in (only an asterisk, *
matches all hosts)
NO_PROXY
If the hostname matches one of these strings, or the host is within
the domain of one of these strings, transactions with that node is not
done over the proxy. When a domain is used, it needs to start with a
period. A user can specify that both www.example.com and foo.example.com
should not use a proxy by setting NO_PROXY
to
.example.com
. By including the full name you can exclude
specific hostnames, so to make www.example.com
not use a
proxy but still have foo.example.com
do it, set
NO_PROXY
to www.example.com
.
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 do not 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, therefore most Unix programs
do not read this file unless it is only readable by yourself (curl does
not 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 simple .netrc
file could look something like:
machine curl.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.example.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.example.com -u username:fakepwd
There is no use for a password on the -u
switch, but a
blank one makes curl ask for one and you already entered the real
password to kinit
/kauth
.
TELNET
The curl telnet support is basic and 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.example.com
Enter the data to pass to the server on stdin. The result is 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.example.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 cannot 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 makes curl transfer all of them, one after the other in the specified order.
libcurl attempts 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 subsequent curl invokes. Try to stuff as many URLs as possible on the same command line if they are using the same host, as that makes the transfers faster. If you use an HTTP proxy for file transfers, practically all transfers are 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://example.com/file.txt ftp://example.com/moo.exe -o moo.jpg
You can also upload multiple files in a similar fashion:
curl -T local1 ftp://example.com/moo.exe -T local2 ftp://example.com/moo2.txt
IPv6
curl connects 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.
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.se/mail/.
Please direct curl questions, feature requests and trouble reports to one of these mailing lists instead of mailing any individual.
Available lists include:
curl-users
Users of the command line tool. How to use it, what does not 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.