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Updated: Jun 9, 2009 (http://curl.haxx.se/docs/faq.html)
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1. Philosophy
1.1 What is cURL?
1.2 What is libcurl?
1.5 Who makes curl?
1.6 What do you get for making curl?
1.7 What about CURL from curl.com?
1.9 Where do I buy commercial support for curl?
1.10 How many are using curl?
Daniel Stenberg
committed
1.11 Why don't you update ca-bundle.crt
2. Install Related Problems
2.1 configure doesn't find OpenSSL even when it is installed
2.1.1 native linker doesn't find OpenSSL
2.1.2 only the libssl lib is missing
2.2 Does curl work/build with other SSL libraries?
2.3 Where can I find a copy of LIBEAY32.DLL?
2.4 Does curl support SOCKS (RFC 1928) ?
3. Usage Problems
3.1 curl: (1) SSL is disabled, https: not supported
3.2 How do I tell curl to resume a transfer?
3.3 Why doesn't my posting using -F work?
3.4 How do I tell curl to run custom FTP commands?
3.5 How can I disable the Pragma: nocache header?
3.6 Does curl support ASP, XML, XHTML or HTML version Y?
3.7 Can I use curl to delete/rename a file through FTP?
3.8 How do I tell curl to follow HTTP redirects?
3.9 How do I use curl in my favorite programming language?
3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
3.11 How do I POST with a different Content-Type?
3.13 Why does my single/double quotes fail?
3.14 Does curl support Javascript or PAC (automated proxy config)?
3.15 Can I do recursive fetches with curl?
3.17 How do I list the root dir of an FTP server?
3.18 Can I use curl to send a POST/PUT and not wait for a response?
4. Running Problems
4.1 Problems connecting to SSL servers.
4.2 Why do I get problems when I use & or % in the URL?
4.3 How can I use {, }, [ or ] to specify multiple URLs?
4.4 Why do I get downloaded data even though the web page doesn't exist?
4.5 Why do I get return code XXX from a HTTP server?
4.5.1 "400 Bad Request"
4.5.2 "401 Unauthorized"
4.5.3 "403 Forbidden"
4.5.4 "404 Not Found"
4.5.5 "405 Method Not Allowed"
4.5.6 "301 Moved Permanently"
4.7 How do I keep user names and passwords secret in Curl command lines?
4.8 I found a bug!
4.9 Curl can't authenticate to the server that requires NTLM?
4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
4.11 Why does my HTTP range requests return the full document?
4.12 Why do I get "certificate verify failed" ?
4.13 Why is curl -R on Windows one hour off?
4.14 Redirects work in browser but not with curl!
4.15 FTPS doesn't work
4.16 My HTTP POST or PUT requests are slow!
4.17 Non-functional connect timeouts on Windows
5.1 Is libcurl thread-safe?
5.2 How can I receive all data into a large memory chunk?
5.4 Does libcurl do Winsock initing on win32 systems?
5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
5.6 What about Keep-Alive or persistent connections?
5.7 Link errors when building libcurl on Windows!
5.8 libcurl.so.3: open failed: No such file or directory
Daniel Stenberg
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5.9 How does libcurl resolve host names?
5.10 How do I prevent libcurl from writing the response to stdout?
5.11 How do I make libcurl not receive the whole HTTP response?
5.12 Can I make libcurl fake or hide my real IP address?
5.13 How do I stop an ongoing transfer?
5.14 Using C++ non-static functions for callbacks?
6. License Issues
6.1 I have a GPL program, can I use the libcurl library?
6.2 I have a closed-source program, can I use the libcurl library?
6.3 I have a BSD licensed program, can I use the libcurl library?
6.4 I have a program that uses LGPL libraries, can I use libcurl?
6.5 Can I modify curl/libcurl for my program and keep the changes secret?
6.6 Can you please change the curl/libcurl license to XXXX?
6.7 What are my obligations when using libcurl in my commercial apps?
7. PHP/CURL Issues
7.1 What is PHP/CURL?
7.2 Who write PHP/CURL?
7.3 Can I perform multiple requests using the same handle?
==============================================================================
1. Philosophy
1.1 What is cURL?
cURL is the name of the project. The name is a play on 'Client for URLs',
originally with URL spelled in uppercase to make it obvious it deals with
URLs. The fact it can also be pronounced 'see URL' also helped, it works as
an abbreviation for "Client URL Request Library" or why not the recursive
libcurl
A free and easy-to-use client-side URL transfer library, supporting FTP,
FTPS, HTTP, HTTPS, SCP, SFTP, TFTP, TELNET, DICT, FILE, LDAP and LDAPS.
libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading,
kerberos, HTTP form based upload, proxies, cookies, user+password
authentication, file transfer resume, http proxy tunneling and more!
libcurl is highly portable, it builds and works identically on numerous
platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX,
IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOs, Mac
OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS and more...
libcurl is free, thread-safe, IPv6 compatible, feature rich, well
supported and fast.
curl
A command line tool for getting or sending files using URL syntax.
Since curl uses libcurl, it supports a range of common Internet protocols,
currently including HTTP, HTTPS, FTP, FTPS, SCP, SFTP, TFTP, LDAP, LDAPS,
DICT, TELNET and FILE.
We pronounce curl and cURL with an initial k sound: [kurl].
There are numerous sub-projects and related projects that also use the word
curl in the project names in various combinations, but you should take
notice that this FAQ is directed at the command-line tool named curl (and
libcurl the library), and may therefore not be valid for other curl-related
projects. (There is however a small section for the PHP/CURL in this FAQ.)
libcurl is a reliable and portable library which provides you with an easy
interface to a range of common Internet protocols.
You can use libcurl for free in your application, be it open source,
commercial or closed-source.
libcurl is most probably the most portable, most powerful and most often
used C-based multi-platform file transfer library on this planet - be it
open source or commercial.
Curl is not a wget clone. That is a common misconception. Never, during
curl's development, have we intended curl to replace wget or compete on its
market. Curl is targeted at single-shot file transfers.
Curl is not a web site mirroring program. If you want to use curl to mirror
something: fine, go ahead and write a script that wraps around curl to make
it reality (like curlmirror.pl does).
Curl is not an FTP site mirroring program. Sure, get and send FTP with curl
but if you want systematic and sequential behavior you should write a
script (or write a new program that interfaces libcurl) and do it.
Curl is not a PHP tool, even though it works perfectly well when used from
Curl is not a program for a single operating system. Curl exists, compiles,
builds and runs under a wide range of operating systems, including all
modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2,
OS X, QNX etc.
We love suggestions of what to change in order to make curl and libcurl
better. We do however believe in a few rules when it comes to the future of
* Curl -- the command line tool -- is to remain a non-graphical command line
tool. If you want GUIs or fancy scripting capabilities, you should look
for another tool that uses libcurl.
* We do not add things to curl that other small and available tools already
do very fine at the side. Curl's output is fine to pipe into another
program or redirect to another file for the next program to interpret.
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