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Updated: August 17, 2000 (http://curl.haxx.se/docs/faq.shtml)
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FAQ FAQ
1. Install Related Problems 1. Philosophy
1.1 configure doesn't find OpenSSL even when it is installed 1.1 What is cURL?
1.1.1. native linker doesn't find openssl 1.2 What is libcurl?
1.1.2. only the libssl lib is missing 1.3 What is cURL not?
1.2 Does curl work/build with other SSL libraries? 1.4 When will you make curl do XXXX ?
1.3 Where can I find a copy of LIBEAY32.DLL?
1.4 Does cURL support Socks (RFC 1928) ?
2. Usage problems 2. Install Related Problems
2.1 curl: (1) SSL is disabled, https: not supported 2.1 configure doesn't find OpenSSL even when it is installed
2.2 How do I tell curl to resume a transfer? 2.1.1. native linker doesn't find openssl
2.3 Why doesn't my posting using -F work? 2.1.2. only the libssl lib is missing
2.4 How do I tell curl to run custom FTP commands? 2.2 Does curl work/build with other SSL libraries?
2.5 How can I disable the Pragma: nocache header? 2.3 Where can I find a copy of LIBEAY32.DLL?
2.6 Does curl support javascript, ASP, XML, XHTML or HTML version Y? 2.4 Does cURL support Socks (RFC 1928) ?
2.7 Can I use curl to delete/rename a file through FTP?
3. Running Problems 3. Usage Problems
3.1 Problems connecting to SSL servers. 3.1 curl: (1) SSL is disabled, https: not supported
3.2 Why do I get problems when I use & in the URL? 3.2 How do I tell curl to resume a transfer?
3.3 How can I use {, }, [ or ] to specify multiple URLs? 3.3 Why doesn't my posting using -F work?
3.4 Why do I get downloaded data even though the web page doesn't exist? 3.4 How do I tell curl to run custom FTP commands?
3.5 Why do I get "HTTP/1.1 403 Forbidden" from a http server? 3.5 How can I disable the Pragma: nocache header?
3.6 Can you tell me what error code 142 means? 3.6 Does curl support javascript, 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?
4. libcurl issues 4. Running Problems
4.1 Is libcurl thread safe? 4.1 Problems connecting to SSL servers.
4.2 Why do I get problems when I use & 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"
4.6 Can you tell me what error code 142 means?
5. license issues 5. libcurl Issues
5.1 I have a GPL program, can I use the libcurl library? 5.1 Is libcurl thread safe?
5.2 I have a closed-source program, can I use the libcurl library?
5.3 I have a program that uses LGPL libraries, can I use libcurl?
5.4 Can I modify curl/libcurl for my program and keep the changes secret?
5.5 Can you please change the curl/libcurl license to XXXX?
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 program that uses LGPL libraries, can I use libcurl?
6.4 Can I modify curl/libcurl for my program and keep the changes secret?
6.5 Can you please change the curl/libcurl license to XXXX?
==============================================================================
1. Install Related Problems 1. Philosophy
1.1. configure doesn't find OpenSSL even when it is installed 1.1 What is cURL?
cURL (or simply just 'curl') is a command line tool for getting or sending
files using URL syntax. The name is a play on 'Client for URLs', originally
with URL spelled in uppercase to make it obvious it deals with URLs.
Curl supports a range of common internet protocols, currently including
HTTP, HTTPS, FTP, GOPHER, LDAP, DICT and FILE.
1.2 What is libcurl?
libcurl is the engine inside curl that does all the work. curl is more or
less the command line interface that converts the given options into libcurl
function invokes. libcurl is a reliable, higly portable multiprotocol file
transfer library.
Any application is free to use libcurl, even commercial or closed-source
ones. Just make sure changes to the lib itself is made public.
1.3 What is cURL not?
Curl is *not*, I repeat, *not* a wget clone even though that is a very
common misconception. Never, during curl's development, have I 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 wanna 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 behaviour 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
or with PHP.
1.4 When will you make curl do XXXX ?
I love suggestions of what to change in order to make curl and libcurl
better. I do however believe in a few rules when it comes to the future of
curl:
* It is to remain a command line tool. If you want GUIs or fancy scripting
capabilities, you're free to write another tool that uses libcurl and that
offers this. There's no point in having one single tool that does every
imaginable thing. That's also one of the great advantages of having the
core of curl as a library: libcurl.
* I 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.
* I focus on protocol related issues and improvements. If you wanna do more
magic with the supported protocols than curl currently does, changes are
big I will agree. If you wanna add more protocols, I may very well
agree.
* If you want me to make all the work while you wait for me to implement it
for you, that is not a very friendly attitude. I spend a considerable time
already on maintaining and developing curl. In order to get more out of
me, I trust you will offer some of your time and efforts in return.
* If you write the code, chances are bigger that it will get into curl
faster.
2. Install Related Problems
2.1. configure doesn't find OpenSSL even when it is installed
This may be because of several reasons. This may be because of several reasons.
1.1.1. native linker doesn't find openssl 2.1.1. native linker doesn't find openssl
Affected platforms: Affected platforms:
Solaris (native cc compiler) Solaris (native cc compiler)
@ -70,7 +151,7 @@ FAQ
Solution submitted by: Bob Allison <allisonb@users.sourceforge.net> Solution submitted by: Bob Allison <allisonb@users.sourceforge.net>
1.1.2. only the libssl lib is missing 2.1.2. only the libssl lib is missing
If all include files and the libcrypto lib is present, with only the If all include files and the libcrypto lib is present, with only the
libssl being missing according to configure, this is mostly likely because libssl being missing according to configure, this is mostly likely because
@ -83,7 +164,7 @@ FAQ
configure. Make sure that you remove the config.cache file before you configure. Make sure that you remove the config.cache file before you
rerun configure with the new flags. rerun configure with the new flags.
1.2. Does curl work/build with other SSL libraries? 2.2. Does curl work/build with other SSL libraries?
Curl has been written to use OpenSSL, although I doubt there would be much Curl has been written to use OpenSSL, although I doubt there would be much
problems using a different library. I just don't know any other free one and problems using a different library. I just don't know any other free one and
@ -92,7 +173,7 @@ FAQ
If anyone does "port" curl to use a commercial SSL library, I am of course If anyone does "port" curl to use a commercial SSL library, I am of course
very interested in getting the patch! very interested in getting the patch!
1.3. Where can I find a copy of LIBEAY32.DLL? 2.3. Where can I find a copy of LIBEAY32.DLL?
That is an OpenSSL binary built for Windows. That is an OpenSSL binary built for Windows.
@ -101,16 +182,16 @@ FAQ
accurate and up-to-date pointers to recent OpenSSL DDLs and other binary accurate and up-to-date pointers to recent OpenSSL DDLs and other binary
packages. packages.
1.4. Does cURL support Socks (RFC 1928) ? 2.4. Does cURL support Socks (RFC 1928) ?
No. Nobody has wanted it that badly yet. I would appriciate patches that No. Nobody has wanted it that badly yet. I would appriciate patches that
brings this functionality. brings this functionality.
2. Usage problems 3. Usage problems
2.1. curl: (1) SSL is disabled, https: not supported 3.1. curl: (1) SSL is disabled, https: not supported
If you get this output when trying to get anything from a https:// server, If you get this output when trying to get anything from a https:// server,
it means that the configure script couldn't find all libs and include files it means that the configure script couldn't find all libs and include files
@ -125,13 +206,13 @@ FAQ
Also, check out the other paragraph in this FAQ labeled "configure doesn't Also, check out the other paragraph in this FAQ labeled "configure doesn't
find OpenSSL even when it is installed". find OpenSSL even when it is installed".
2.2. How do I tell curl to resume a transfer? 3.2. How do I tell curl to resume a transfer?
Curl supports resume both ways on FTP, download ways on HTTP. Curl supports resume both ways on FTP, download ways on HTTP.
Try the -c and -C options. Try the -c and -C options.
2.3. Why doesn't my posting using -F work? 3.3. Why doesn't my posting using -F work?
You can't simply use -F or -d at your choice. The web server that will You can't simply use -F or -d at your choice. The web server that will
receive your post assumes one of the formats. If the form you're trying to receive your post assumes one of the formats. If the form you're trying to
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about this to the mailing list. I would also suggest that you read through about this to the mailing list. I would also suggest that you read through
the mailing list archives for old postings and questions regarding this. the mailing list archives for old postings and questions regarding this.
2.4. How do I tell curl to run custom FTP commands? 3.4. How do I tell curl to run custom FTP commands?
You can tell curl to perform optional commands both before and/or after a You can tell curl to perform optional commands both before and/or after a
file transfer. Study the -Q/--quote option. file transfer. Study the -Q/--quote option.
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ftp commands without transfering anything. Therefore you must always specify ftp commands without transfering anything. Therefore you must always specify
a URL to transfer to/from even when doing custom FTP commands. a URL to transfer to/from even when doing custom FTP commands.
2.5. How can I disable the Pragma: nocache header? 3.5. How can I disable the Pragma: nocache header?
You can change all internally generated headers by adding a replacement with You can change all internally generated headers by adding a replacement with
the -H/--header option. By adding a header with empty contents you safely the -H/--header option. By adding a header with empty contents you safely
disable that one. Use -H "Pragma:" to disable that specific header. disable that one. Use -H "Pragma:" to disable that specific header.
2.6. Does curl support javascript, ASP, XML, XHTML or HTML version Y? 3.6. Does curl support javascript, ASP, XML, XHTML or HTML version Y?
To curl, all contents are alike. It doesn't matter how the page was To curl, all contents are alike. It doesn't matter how the page was
generated. It may be ASP, PHP, perl, shell-script, SSI or plain generated. It may be ASP, PHP, perl, shell-script, SSI or plain
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that is sent for the client to interpret and curl has no javascript that is sent for the client to interpret and curl has no javascript
interpreter. interpreter.
2.7. Can I use curl to delete/rename a file through FTP? 3.7. Can I use curl to delete/rename a file through FTP?
Yes. You specify custom ftp commands with -Q/--quote. Yes. You specify custom ftp commands with -Q/--quote.
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curl -O ftp://download.com/coolfile -Q '-DELE coolfile' curl -O ftp://download.com/coolfile -Q '-DELE coolfile'
3.8 How do I tell curl to follow HTTP redirects?
3. Running Problems Curl does not follow so-called redirects by default. The Location: header
that informs the client about this is only interpreted if you're using the
-L/--location option. As in:
3.1. Problems connecting to SSL servers. curl -L http://redirector.com
4. Running Problems
4.1. Problems connecting to SSL servers.
It took a very long time before I could sort out why curl had problems It took a very long time before I could sort out why curl had problems
to connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. to connect to certain SSL servers when using SSLeay or OpenSSL v0.9+.
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I have also seen examples where the remote server didn't like the SSLv2 I have also seen examples where the remote server didn't like the SSLv2
request and instead you had to force curl to use SSLv3 with -3/--sslv3. request and instead you had to force curl to use SSLv3 with -3/--sslv3.
3.2. Why do I get problems when I use & in the URL? 4.2. Why do I get problems when I use & in the URL?
In general unix shells, the & letter is treated special and when used it In general unix shells, the & letter is treated special and when used it
runs the specified command in the background. To safely send the & as a part runs the specified command in the background. To safely send the & as a part
@ -207,7 +295,7 @@ FAQ
curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl' curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl'
3.3. How can I use {, }, [ or ] to specify multiple URLs? 4.3. How can I use {, }, [ or ] to specify multiple URLs?
Because those letters have a special meaning to the shell, and to be used in Because those letters have a special meaning to the shell, and to be used in
a URL specified to curl you must quote them. a URL specified to curl you must quote them.
@ -216,7 +304,7 @@ FAQ
curl '{curl,www}.haxx.se' curl '{curl,www}.haxx.se'
3.4. Why do I get downloaded data even though the web page doesn't exist? 4.4. Why do I get downloaded data even though the web page doesn't exist?
Curl asks remote servers for the page you specify. If the page doesn't exist Curl asks remote servers for the page you specify. If the page doesn't exist
at the server, the HTTP protocol defines how the server should respond and at the server, the HTTP protocol defines how the server should respond and
@ -226,28 +314,44 @@ FAQ
By using the --fail option you can tell curl explicitly to not get any data By using the --fail option you can tell curl explicitly to not get any data
if the HTTP return code doesn't say success. if the HTTP return code doesn't say success.
3.5. Why do I get "HTTP/1.1 403 Forbidden" from a http server? 4.5 Why do I get return code XXX from a HTTP server?
RFC2616 clearly explains this return code: RFC2616 clearly explains the return codes. I'll make a short transcript
here. Go read the RFC for exact details:
"10.4.4 403 Forbidden" 4.5.1 "400 Bad Request"
The server understood the request, but is refusing to fulfill it. The request could not be understood by the server due to malformed
Authorization will not help and the request SHOULD NOT be repeated. If the syntax. The client SHOULD NOT repeat the request without modifications.
request method was not HEAD and the server wishes to make public why the
request has not been fulfilled, it SHOULD describe the reason for the
refusal in the entity. If the server does not wish to make this information
available to the client, the status code 404 (Not Found) can be used
instead.
3.6. Can you tell me what error code 142 means? 4.5.2 "401 Unauthorized"
The request requires user authentication.
4.5.3 "403 Forbidden"
The server understood the request, but is refusing to fulfill it.
Authorization will not help and the request SHOULD NOT be repeated.
4.5.4 "404 Not Found"
The server has not found anything matching the Request-URI. No indication
is given of whether the condition is temporary or permanent.
4.5.5 "405 Method Not Allowed"
The method specified in the Request-Line is not allowed for the resource
identified by the Request-URI. The response MUST include an Allow header
containing a list of valid methods for the requested resource.
4.6. Can you tell me what error code 142 means?
All error codes that are larger than the highest documented error code means All error codes that are larger than the highest documented error code means
that curl has existed due to a timeout. There is currentl no nice way for that curl has existed due to a timeout. There is currentl no nice way for
curl to abort from such a condition and that's why it gets this undocumented curl to abort from such a condition and that's why it gets this undocumented
error. This is planned to change in a future release. error. This is planned to change in a future release.
3.7. How do I keep usernames and passwords secret in Curl command lines? 4.7. How do I keep usernames and passwords secret in Curl command lines?
I see this problem as two parts: I see this problem as two parts:
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anyone would call security. anyone would call security.
4. libcurl issues 5. libcurl Issues
4.1. Is libcurl thread safe? 5.1. Is libcurl thread safe?
As version seven is slowly marching in as the libcurl version to use, we As version seven is slowly marching in as the libcurl version to use, we
have made a serious attempt to address all places in the code where we could have made a serious attempt to address all places in the code where we could
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README file from those who have used libcurl in a threaded environment, README file from those who have used libcurl in a threaded environment,
since I haven't and I get this question more and more frequently! since I haven't and I get this question more and more frequently!
5. license issues 6. License Issues
Curl and libcurl are released under the MPL, the Mozilla Public License. To Curl and libcurl are released under the MPL, the Mozilla Public License. To
get a really good answer to this or other licensing questions, you should get a really good answer to this or other licensing questions, you should
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clashes yourself. This is a brief summary for a few cases for which we get clashes yourself. This is a brief summary for a few cases for which we get
questions: questions:
5.1. I have a GPL program, can I use the libcurl library? 6.1. I have a GPL program, can I use the libcurl library?
No, you can't distribute your program as a binary and you cannot No, you can't distribute your program as a binary and you cannot
distribute the (lib)curl code your code. GPL'd software requires all parts distribute the (lib)curl code with your code. GPL'd software requires all
of the final executable to be licensed under GPL. parts of the final executable to be licensed under GPL or a license that
"does impose further restrictions". (One could argue about which license
that acutally imposes the restrictions, but that'll be left for you to
ponder about.) MPL is not compatible with GPL.
However, nothing prevents you from distributing your program separately However, nothing prevents you from distributing your program separately
from curl and libcurl and require the user to get it separately. from curl and libcurl and request that the user gets it separately.
5.2. I have a closed-source program, can I use the libcurl library? 6.2. I have a closed-source program, can I use the libcurl library?
Yes, libcurl does not put any restrictions on the program that uses the Yes, libcurl does not put any restrictions on the program that uses the
library. If you end up doing changes to the library, only those changes library. If you end up doing changes to the library, only those changes
must be made available, not the ones to your program. must be made available, not the ones to your program.
5.3. I have a program that uses LGPL libraries, can I use libcurl? 6.3. I have a program that uses LGPL libraries, can I use libcurl?
Yes you can. LGPL libraries don't spread to other libraries the same way Yes you can. LGPL libraries don't spread to other libraries the same way
GPL ones do. GPL ones do.
5.4. Can I modify curl/libcurl for my program and keep the changes secret? However, when you read paragraph (3) of the LGPL license, you'll see that
anyone - at will - may at any time convert that LGPL program into GPL. And
GPL programs can't be distributed together, neither with (lib)curl source
code and not as a binary.
6.4. Can I modify curl/libcurl for my program and keep the changes secret?
No, you're not allowed to do that. No, you're not allowed to do that.
5.5. Can you please change the curl/libcurl license to XXXX? 6.5. Can you please change the curl/libcurl license to XXXX?
No. We carefully picked this license years ago and a large amount of No. We carefully picked this license years ago and a large amount of
people have contributed with source code knowing that this is the license people have contributed with source code knowing that this is the license
we use. This license puts the restrictions we want on curl/libcurl and it we use. This license puts the restrictions we want on curl/libcurl and it
does not spread to other programs or libraries. does not spread to other programs or libraries that use it.