1# curl tutorial 2 3## Simple Usage 4 5Get the main page from Netscape's web-server: 6 7 curl http://www.netscape.com/ 8 9Get the README file the user's home directory at funet's ftp-server: 10 11 curl ftp://ftp.funet.fi/README 12 13Get a web page from a server using port 8000: 14 15 curl http://www.weirdserver.com:8000/ 16 17Get a directory listing of an FTP site: 18 19 curl ftp://cool.haxx.se/ 20 21Get the definition of curl from a dictionary: 22 23 curl dict://dict.org/m:curl 24 25Fetch two documents at once: 26 27 curl ftp://cool.haxx.se/ http://www.weirdserver.com:8000/ 28 29Get a file off an FTPS server: 30 31 curl ftps://files.are.secure.com/secrets.txt 32 33or use the more appropriate FTPS way to get the same file: 34 35 curl --ftp-ssl ftp://files.are.secure.com/secrets.txt 36 37Get a file from an SSH server using SFTP: 38 39 curl -u username sftp://example.com/etc/issue 40 41Get a file from an SSH server using SCP using a private key (not 42password-protected) to authenticate: 43 44 curl -u username: --key ~/.ssh/id_rsa scp://example.com/~/file.txt 45 46Get a file from an SSH server using SCP using a private key 47(password-protected) to authenticate: 48 49 curl -u username: --key ~/.ssh/id_rsa --pass private_key_password 50 scp://example.com/~/file.txt 51 52Get the main page from an IPv6 web server: 53 54 curl "http://[2001:1890:1112:1::20]/" 55 56Get a file from an SMB server: 57 58 curl -u "domain\username:passwd" smb://server.example.com/share/file.txt 59 60## Download to a File 61 62Get a web page and store in a local file with a specific name: 63 64 curl -o thatpage.html http://www.netscape.com/ 65 66Get a web page and store in a local file, make the local file get the name of 67the remote document (if no file name part is specified in the URL, this will 68fail): 69 70 curl -O http://www.netscape.com/index.html 71 72Fetch two files and store them with their remote names: 73 74 curl -O www.haxx.se/index.html -O curl.haxx.se/download.html 75 76## Using Passwords 77 78### FTP 79 80To ftp files using name+passwd, include them in the URL like: 81 82 curl ftp://name:passwd@machine.domain:port/full/path/to/file 83 84or specify them with the -u flag like 85 86 curl -u name:passwd ftp://machine.domain:port/full/path/to/file 87 88### FTPS 89 90It is just like for FTP, but you may also want to specify and use SSL-specific 91options for certificates etc. 92 93Note that using `FTPS://` as prefix is the "implicit" way as described in the 94standards while the recommended "explicit" way is done by using FTP:// and the 95`--ftp-ssl` option. 96 97### SFTP / SCP 98 99This is similar to FTP, but you can use the `--key` option to specify a 100private key to use instead of a password. Note that the private key may itself 101be protected by a password that is unrelated to the login password of the 102remote system; this password is specified using the `--pass` option. 103Typically, curl will automatically extract the public key from the private key 104file, but in cases where curl does not have the proper library support, a 105matching public key file must be specified using the `--pubkey` option. 106 107### HTTP 108 109Curl also supports user and password in HTTP URLs, thus you can pick a file 110like: 111 112 curl http://name:passwd@machine.domain/full/path/to/file 113 114or specify user and password separately like in 115 116 curl -u name:passwd http://machine.domain/full/path/to/file 117 118HTTP offers many different methods of authentication and curl supports 119several: Basic, Digest, NTLM and Negotiate (SPNEGO). Without telling which 120method to use, curl defaults to Basic. You can also ask curl to pick the most 121secure ones out of the ones that the server accepts for the given URL, by 122using `--anyauth`. 123 124**Note**! According to the URL specification, HTTP URLs can not contain a user 125and password, so that style will not work when using curl via a proxy, even 126though curl allows it at other times. When using a proxy, you _must_ use the 127`-u` style for user and password. 128 129### HTTPS 130 131Probably most commonly used with private certificates, as explained below. 132 133## Proxy 134 135curl supports both HTTP and SOCKS proxy servers, with optional authentication. 136It does not have special support for FTP proxy servers since there are no 137standards for those, but it can still be made to work with many of them. You 138can also use both HTTP and SOCKS proxies to transfer files to and from FTP 139servers. 140 141Get an ftp file using an HTTP proxy named my-proxy that uses port 888: 142 143 curl -x my-proxy:888 ftp://ftp.leachsite.com/README 144 145Get a file from an HTTP server that requires user and password, using the 146same proxy as above: 147 148 curl -u user:passwd -x my-proxy:888 http://www.get.this/ 149 150Some proxies require special authentication. Specify by using -U as above: 151 152 curl -U user:passwd -x my-proxy:888 http://www.get.this/ 153 154A comma-separated list of hosts and domains which do not use the proxy can be 155specified as: 156 157 curl --noproxy localhost,get.this -x my-proxy:888 http://www.get.this/ 158 159If the proxy is specified with `--proxy1.0` instead of `--proxy` or `-x`, then 160curl will use HTTP/1.0 instead of HTTP/1.1 for any `CONNECT` attempts. 161 162curl also supports SOCKS4 and SOCKS5 proxies with `--socks4` and `--socks5`. 163 164See also the environment variables Curl supports that offer further proxy 165control. 166 167Most FTP proxy servers are set up to appear as a normal FTP server from the 168client's perspective, with special commands to select the remote FTP server. 169curl supports the `-u`, `-Q` and `--ftp-account` options that can be used to 170set up transfers through many FTP proxies. For example, a file can be uploaded 171to a remote FTP server using a Blue Coat FTP proxy with the options: 172 173 curl -u "username@ftp.server Proxy-Username:Remote-Pass" 174 --ftp-account Proxy-Password --upload-file local-file 175 ftp://my-ftp.proxy.server:21/remote/upload/path/ 176 177See the manual for your FTP proxy to determine the form it expects to set up 178transfers, and curl's `-v` option to see exactly what curl is sending. 179 180## Ranges 181 182HTTP 1.1 introduced byte-ranges. Using this, a client can request to get only 183one or more subparts of a specified document. Curl supports this with the `-r` 184flag. 185 186Get the first 100 bytes of a document: 187 188 curl -r 0-99 http://www.get.this/ 189 190Get the last 500 bytes of a document: 191 192 curl -r -500 http://www.get.this/ 193 194Curl also supports simple ranges for FTP files as well. Then you can only 195specify start and stop position. 196 197Get the first 100 bytes of a document using FTP: 198 199 curl -r 0-99 ftp://www.get.this/README 200 201## Uploading 202 203### FTP / FTPS / SFTP / SCP 204 205Upload all data on stdin to a specified server: 206 207 curl -T - ftp://ftp.upload.com/myfile 208 209Upload data from a specified file, login with user and password: 210 211 curl -T uploadfile -u user:passwd ftp://ftp.upload.com/myfile 212 213Upload a local file to the remote site, and use the local file name at the 214remote site too: 215 216 curl -T uploadfile -u user:passwd ftp://ftp.upload.com/ 217 218Upload a local file to get appended to the remote file: 219 220 curl -T localfile -a ftp://ftp.upload.com/remotefile 221 222Curl also supports ftp upload through a proxy, but only if the proxy is 223configured to allow that kind of tunneling. If it does, you can run curl in a 224fashion similar to: 225 226 curl --proxytunnel -x proxy:port -T localfile ftp.upload.com 227 228### SMB / SMBS 229 230 curl -T file.txt -u "domain\username:passwd" 231 smb://server.example.com/share/ 232 233### HTTP 234 235Upload all data on stdin to a specified HTTP site: 236 237 curl -T - http://www.upload.com/myfile 238 239Note that the HTTP server must have been configured to accept PUT before this 240can be done successfully. 241 242For other ways to do HTTP data upload, see the POST section below. 243 244## Verbose / Debug 245 246If curl fails where it isn't supposed to, if the servers don't let you in, if 247you can't understand the responses: use the `-v` flag to get verbose 248fetching. Curl will output lots of info and what it sends and receives in 249order to let the user see all client-server interaction (but it won't show you 250the actual data). 251 252 curl -v ftp://ftp.upload.com/ 253 254To get even more details and information on what curl does, try using the 255`--trace` or `--trace-ascii` options with a given file name to log to, like 256this: 257 258 curl --trace trace.txt www.haxx.se 259 260 261## Detailed Information 262 263Different protocols provide different ways of getting detailed information 264about specific files/documents. To get curl to show detailed information about 265a single file, you should use `-I`/`--head` option. It displays all available 266info on a single file for HTTP and FTP. The HTTP information is a lot more 267extensive. 268 269For HTTP, you can get the header information (the same as `-I` would show) 270shown before the data by using `-i`/`--include`. Curl understands the 271`-D`/`--dump-header` option when getting files from both FTP and HTTP, and it 272will then store the headers in the specified file. 273 274Store the HTTP headers in a separate file (headers.txt in the example): 275 276 curl --dump-header headers.txt curl.haxx.se 277 278Note that headers stored in a separate file can be very useful at a later time 279if you want curl to use cookies sent by the server. More about that in the 280cookies section. 281 282## POST (HTTP) 283 284It's easy to post data using curl. This is done using the `-d <data>` option. 285The post data must be urlencoded. 286 287Post a simple "name" and "phone" guestbook. 288 289 curl -d "name=Rafael%20Sagula&phone=3320780" http://www.where.com/guest.cgi 290 291How to post a form with curl, lesson #1: 292 293Dig out all the `<input>` tags in the form that you want to fill in. 294 295If there's a "normal" post, you use `-d` to post. `-d` takes a full "post 296string", which is in the format 297 298 <variable1>=<data1>&<variable2>=<data2>&... 299 300The 'variable' names are the names set with `"name="` in the `<input>` tags, 301and the data is the contents you want to fill in for the inputs. The data 302*must* be properly URL encoded. That means you replace space with + and that 303you replace weird letters with %XX where XX is the hexadecimal representation 304of the letter's ASCII code. 305 306Example: 307 308(page located at `http://www.formpost.com/getthis/`) 309 310 <form action="post.cgi" method="post"> 311 <input name=user size=10> 312 <input name=pass type=password size=10> 313 <input name=id type=hidden value="blablabla"> 314 <input name=ding value="submit"> 315 </form> 316 317We want to enter user 'foobar' with password '12345'. 318 319To post to this, you enter a curl command line like: 320 321 curl -d "user=foobar&pass=12345&id=blablabla&ding=submit" 322 http://www.formpost.com/getthis/post.cgi 323 324While `-d` uses the application/x-www-form-urlencoded mime-type, generally 325understood by CGI's and similar, curl also supports the more capable 326multipart/form-data type. This latter type supports things like file upload. 327 328`-F` accepts parameters like `-F "name=contents"`. If you want the contents to 329be read from a file, use `@filename` as contents. When specifying a file, you 330can also specify the file content type by appending `;type=<mime type>` to the 331file name. You can also post the contents of several files in one field. For 332example, the field name 'coolfiles' is used to send three files, with 333different content types using the following syntax: 334 335 curl -F "coolfiles=@fil1.gif;type=image/gif,fil2.txt,fil3.html" 336 http://www.post.com/postit.cgi 337 338If the content-type is not specified, curl will try to guess from the file 339extension (it only knows a few), or use the previously specified type (from an 340earlier file if several files are specified in a list) or else it will use the 341default type 'application/octet-stream'. 342 343Emulate a fill-in form with `-F`. Let's say you fill in three fields in a 344form. One field is a file name which to post, one field is your name and one 345field is a file description. We want to post the file we have written named 346"cooltext.txt". To let curl do the posting of this data instead of your 347favourite browser, you have to read the HTML source of the form page and find 348the names of the input fields. In our example, the input field names are 349'file', 'yourname' and 'filedescription'. 350 351 curl -F "file=@cooltext.txt" -F "yourname=Daniel" 352 -F "filedescription=Cool text file with cool text inside" 353 http://www.post.com/postit.cgi 354 355To send two files in one post you can do it in two ways: 356 357Send multiple files in a single "field" with a single field name: 358 359 curl -F "pictures=@dog.gif,cat.gif" $URL 360 361Send two fields with two field names 362 363 curl -F "docpicture=@dog.gif" -F "catpicture=@cat.gif" $URL 364 365To send a field value literally without interpreting a leading `@` or `<`, or 366an embedded `;type=`, use `--form-string` instead of `-F`. This is recommended 367when the value is obtained from a user or some other unpredictable 368source. Under these circumstances, using `-F` instead of `--form-string` could 369allow a user to trick curl into uploading a file. 370 371## Referrer 372 373An HTTP request has the option to include information about which address 374referred it to the actual page. Curl allows you to specify the referrer to be 375used on the command line. It is especially useful to fool or trick stupid 376servers or CGI scripts that rely on that information being available or 377contain certain data. 378 379 curl -e www.coolsite.com http://www.showme.com/ 380 381## User Agent 382 383An HTTP request has the option to include information about the browser that 384generated the request. Curl allows it to be specified on the command line. It 385is especially useful to fool or trick stupid servers or CGI scripts that only 386accept certain browsers. 387 388Example: 389 390 curl -A 'Mozilla/3.0 (Win95; I)' http://www.nationsbank.com/ 391 392Other common strings: 393 394- `Mozilla/3.0 (Win95; I)` - Netscape Version 3 for Windows 95 395- `Mozilla/3.04 (Win95; U)` - Netscape Version 3 for Windows 95 396- `Mozilla/2.02 (OS/2; U)` - Netscape Version 2 for OS/2 397- `Mozilla/4.04 [en] (X11; U; AIX 4.2; Nav)` - Netscape for AIX 398- `Mozilla/4.05 [en] (X11; U; Linux 2.0.32 i586)` - Netscape for Linux 399 400Note that Internet Explorer tries hard to be compatible in every way: 401 402- `Mozilla/4.0 (compatible; MSIE 4.01; Windows 95)` - MSIE for W95 403 404Mozilla is not the only possible User-Agent name: 405 406- `Konqueror/1.0` - KDE File Manager desktop client 407- `Lynx/2.7.1 libwww-FM/2.14` - Lynx command line browser 408 409## Cookies 410 411Cookies are generally used by web servers to keep state information at the 412client's side. The server sets cookies by sending a response line in the 413headers that looks like `Set-Cookie: <data>` where the data part then 414typically contains a set of `NAME=VALUE` pairs (separated by semicolons `;` 415like `NAME1=VALUE1; NAME2=VALUE2;`). The server can also specify for what path 416the "cookie" should be used for (by specifying `path=value`), when the cookie 417should expire (`expire=DATE`), for what domain to use it (`domain=NAME`) and 418if it should be used on secure connections only (`secure`). 419 420If you've received a page from a server that contains a header like: 421 422 Set-Cookie: sessionid=boo123; path="/foo"; 423 424it means the server wants that first pair passed on when we get anything in a 425path beginning with "/foo". 426 427Example, get a page that wants my name passed in a cookie: 428 429 curl -b "name=Daniel" www.sillypage.com 430 431Curl also has the ability to use previously received cookies in following 432sessions. If you get cookies from a server and store them in a file in a 433manner similar to: 434 435 curl --dump-header headers www.example.com 436 437... you can then in a second connect to that (or another) site, use the 438cookies from the 'headers' file like: 439 440 curl -b headers www.example.com 441 442While saving headers to a file is a working way to store cookies, it is 443however error-prone and not the preferred way to do this. Instead, make curl 444save the incoming cookies using the well-known netscape cookie format like 445this: 446 447 curl -c cookies.txt www.example.com 448 449Note that by specifying `-b` you enable the "cookie awareness" and with `-L` 450you can make curl follow a location: (which often is used in combination with 451cookies). So that if a site sends cookies and a location, you can use a 452non-existing file to trigger the cookie awareness like: 453 454 curl -L -b empty.txt www.example.com 455 456The file to read cookies from must be formatted using plain HTTP headers OR as 457netscape's cookie file. Curl will determine what kind it is based on the file 458contents. In the above command, curl will parse the header and store the 459cookies received from www.example.com. curl will send to the server the 460stored cookies which match the request as it follows the location. The file 461"empty.txt" may be a nonexistent file. 462 463To read and write cookies from a netscape cookie file, you can set both `-b` 464and `-c` to use the same file: 465 466 curl -b cookies.txt -c cookies.txt www.example.com 467 468## Progress Meter 469 470The progress meter exists to show a user that something actually is 471happening. The different fields in the output have the following meaning: 472 473 % Total % Received % Xferd Average Speed Time Curr. 474 Dload Upload Total Current Left Speed 475 0 151M 0 38608 0 0 9406 0 4:41:43 0:00:04 4:41:39 9287 476 477From left-to-right: 478 479 - % - percentage completed of the whole transfer 480 - Total - total size of the whole expected transfer 481 - % - percentage completed of the download 482 - Received - currently downloaded amount of bytes 483 - % - percentage completed of the upload 484 - Xferd - currently uploaded amount of bytes 485 - Average Speed Dload - the average transfer speed of the download 486 - Average Speed Upload - the average transfer speed of the upload 487 - Time Total - expected time to complete the operation 488 - Time Current - time passed since the invoke 489 - Time Left - expected time left to completion 490 - Curr.Speed - the average transfer speed the last 5 seconds (the first 491 5 seconds of a transfer is based on less time of course.) 492 493The `-#` option will display a totally different progress bar that doesn't 494need much explanation! 495 496## Speed Limit 497 498Curl allows the user to set the transfer speed conditions that must be met to 499let the transfer keep going. By using the switch `-y` and `-Y` you can make 500curl abort transfers if the transfer speed is below the specified lowest limit 501for a specified time. 502 503To have curl abort the download if the speed is slower than 3000 bytes per 504second for 1 minute, run: 505 506 curl -Y 3000 -y 60 www.far-away-site.com 507 508This can very well be used in combination with the overall time limit, so 509that the above operation must be completed in whole within 30 minutes: 510 511 curl -m 1800 -Y 3000 -y 60 www.far-away-site.com 512 513Forcing curl not to transfer data faster than a given rate is also possible, 514which might be useful if you're using a limited bandwidth connection and you 515don't want your transfer to use all of it (sometimes referred to as 516"bandwidth throttle"). 517 518Make curl transfer data no faster than 10 kilobytes per second: 519 520 curl --limit-rate 10K www.far-away-site.com 521 522or 523 524 curl --limit-rate 10240 www.far-away-site.com 525 526Or prevent curl from uploading data faster than 1 megabyte per second: 527 528 curl -T upload --limit-rate 1M ftp://uploadshereplease.com 529 530When using the `--limit-rate` option, the transfer rate is regulated on a 531per-second basis, which will cause the total transfer speed to become lower 532than the given number. Sometimes of course substantially lower, if your 533transfer stalls during periods. 534 535## Config File 536 537Curl automatically tries to read the `.curlrc` file (or `_curlrc` file on 538Microsoft Windows systems) from the user's home dir on startup. 539 540The config file could be made up with normal command line switches, but you 541can also specify the long options without the dashes to make it more 542readable. You can separate the options and the parameter with spaces, or with 543`=` or `:`. Comments can be used within the file. If the first letter on a 544line is a `#`-symbol the rest of the line is treated as a comment. 545 546If you want the parameter to contain spaces, you must enclose the entire 547parameter within double quotes (`"`). Within those quotes, you specify a quote 548as `\"`. 549 550NOTE: You must specify options and their arguments on the same line. 551 552Example, set default time out and proxy in a config file: 553 554 # We want a 30 minute timeout: 555 -m 1800 556 # ... and we use a proxy for all accesses: 557 proxy = proxy.our.domain.com:8080 558 559White spaces ARE significant at the end of lines, but all white spaces leading 560up to the first characters of each line are ignored. 561 562Prevent curl from reading the default file by using -q as the first command 563line parameter, like: 564 565 curl -q www.thatsite.com 566 567Force curl to get and display a local help page in case it is invoked without 568URL by making a config file similar to: 569 570 # default url to get 571 url = "http://help.with.curl.com/curlhelp.html" 572 573You can specify another config file to be read by using the `-K`/`--config` 574flag. If you set config file name to `-` it'll read the config from stdin, 575which can be handy if you want to hide options from being visible in process 576tables etc: 577 578 echo "user = user:passwd" | curl -K - http://that.secret.site.com 579 580## Extra Headers 581 582When using curl in your own very special programs, you may end up needing 583to pass on your own custom headers when getting a web page. You can do 584this by using the `-H` flag. 585 586Example, send the header `X-you-and-me: yes` to the server when getting a 587page: 588 589 curl -H "X-you-and-me: yes" www.love.com 590 591This can also be useful in case you want curl to send a different text in a 592header than it normally does. The `-H` header you specify then replaces the 593header curl would normally send. If you replace an internal header with an 594empty one, you prevent that header from being sent. To prevent the `Host:` 595header from being used: 596 597 curl -H "Host:" www.server.com 598 599## FTP and Path Names 600 601Do note that when getting files with a `ftp://` URL, the given path is 602relative the directory you enter. To get the file `README` from your home 603directory at your ftp site, do: 604 605 curl ftp://user:passwd@my.site.com/README 606 607But if you want the README file from the root directory of that very same 608site, you need to specify the absolute file name: 609 610 curl ftp://user:passwd@my.site.com//README 611 612(I.e with an extra slash in front of the file name.) 613 614## SFTP and SCP and Path Names 615 616With sftp: and scp: URLs, the path name given is the absolute name on the 617server. To access a file relative to the remote user's home directory, prefix 618the file with `/~/` , such as: 619 620 curl -u $USER sftp://home.example.com/~/.bashrc 621 622## FTP and Firewalls 623 624The FTP protocol requires one of the involved parties to open a second 625connection as soon as data is about to get transferred. There are two ways to 626do this. 627 628The default way for curl is to issue the PASV command which causes the server 629to open another port and await another connection performed by the 630client. This is good if the client is behind a firewall that doesn't allow 631incoming connections. 632 633 curl ftp.download.com 634 635If the server, for example, is behind a firewall that doesn't allow 636connections on ports other than 21 (or if it just doesn't support the `PASV` 637command), the other way to do it is to use the `PORT` command and instruct the 638server to connect to the client on the given IP number and port (as parameters 639to the PORT command). 640 641The `-P` flag to curl supports a few different options. Your machine may have 642several IP-addresses and/or network interfaces and curl allows you to select 643which of them to use. Default address can also be used: 644 645 curl -P - ftp.download.com 646 647Download with `PORT` but use the IP address of our `le0` interface (this does 648not work on windows): 649 650 curl -P le0 ftp.download.com 651 652Download with `PORT` but use 192.168.0.10 as our IP address to use: 653 654 curl -P 192.168.0.10 ftp.download.com 655 656## Network Interface 657 658Get a web page from a server using a specified port for the interface: 659 660 curl --interface eth0:1 http://www.netscape.com/ 661 662or 663 664 curl --interface 192.168.1.10 http://www.netscape.com/ 665 666## HTTPS 667 668Secure HTTP requires a TLS library to be installed and used when curl is 669built. If that is done, curl is capable of retrieving and posting documents 670using the HTTPS protocol. 671 672Example: 673 674 curl https://www.secure-site.com 675 676curl is also capable of using client certificates to get/post files from sites 677that require valid certificates. The only drawback is that the certificate 678needs to be in PEM-format. PEM is a standard and open format to store 679certificates with, but it is not used by the most commonly used browsers. If 680you want curl to use the certificates you use with your (favourite) browser, 681you may need to download/compile a converter that can convert your browser's 682formatted certificates to PEM formatted ones. 683 684Example on how to automatically retrieve a document using a certificate with a 685personal password: 686 687 curl -E /path/to/cert.pem:password https://secure.site.com/ 688 689If you neglect to specify the password on the command line, you will be 690prompted for the correct password before any data can be received. 691 692Many older HTTPS servers have problems with specific SSL or TLS versions, 693which newer versions of OpenSSL etc use, therefore it is sometimes useful to 694specify what SSL-version curl should use. Use -3, -2 or -1 to specify that 695exact SSL version to use (for SSLv3, SSLv2 or TLSv1 respectively): 696 697 curl -2 https://secure.site.com/ 698 699Otherwise, curl will attempt to use a sensible TLS default version. 700 701## Resuming File Transfers 702 703To continue a file transfer where it was previously aborted, curl supports 704esume on HTTP(S) downloads as well as FTP uploads and downloads. 705 706Continue downloading a document: 707 708 curl -C - -o file ftp://ftp.server.com/path/file 709 710Continue uploading a document: 711 712 curl -C - -T file ftp://ftp.server.com/path/file 713 714Continue downloading a document from a web server 715 716 curl -C - -o file http://www.server.com/ 717 718## Time Conditions 719 720HTTP allows a client to specify a time condition for the document it requests. 721It is `If-Modified-Since` or `If-Unmodified-Since`. curl allows you to specify 722them with the `-z`/`--time-cond` flag. 723 724For example, you can easily make a download that only gets performed if the 725remote file is newer than a local copy. It would be made like: 726 727 curl -z local.html http://remote.server.com/remote.html 728 729Or you can download a file only if the local file is newer than the remote 730one. Do this by prepending the date string with a `-`, as in: 731 732 curl -z -local.html http://remote.server.com/remote.html 733 734You can specify a "free text" date as condition. Tell curl to only download 735the file if it was updated since January 12, 2012: 736 737 curl -z "Jan 12 2012" http://remote.server.com/remote.html 738 739Curl will then accept a wide range of date formats. You always make the date 740check the other way around by prepending it with a dash (`-`). 741 742## DICT 743 744For fun try 745 746 curl dict://dict.org/m:curl 747 curl dict://dict.org/d:heisenbug:jargon 748 curl dict://dict.org/d:daniel:web1913 749 750Aliases for 'm' are 'match' and 'find', and aliases for 'd' are 'define' and 751'lookup'. For example, 752 753 curl dict://dict.org/find:curl 754 755Commands that break the URL description of the RFC (but not the DICT 756protocol) are 757 758 curl dict://dict.org/show:db 759 curl dict://dict.org/show:strat 760 761Authentication support is still missing 762 763## LDAP 764 765If you have installed the OpenLDAP library, curl can take advantage of it and 766offer `ldap://` support. On Windows, curl will use WinLDAP from Platform SDK 767by default. 768 769Default protocol version used by curl is LDAPv3. LDAPv2 will be used as 770fallback mechanism in case if LDAPv3 will fail to connect. 771 772LDAP is a complex thing and writing an LDAP query is not an easy task. I do 773advise you to dig up the syntax description for that elsewhere. One such place 774might be: [RFC 2255, The LDAP URL 775Format](https://curl.haxx.se/rfc/rfc2255.txt) 776 777To show you an example, this is how I can get all people from my local LDAP 778server that has a certain sub-domain in their email address: 779 780 curl -B "ldap://ldap.frontec.se/o=frontec??sub?mail=*sth.frontec.se" 781 782If I want the same info in HTML format, I can get it by not using the `-B` 783(enforce ASCII) flag. 784 785You also can use authentication when accessing LDAP catalog: 786 787 curl -u user:passwd "ldap://ldap.frontec.se/o=frontec??sub?mail=*" 788 curl "ldap://user:passwd@ldap.frontec.se/o=frontec??sub?mail=*" 789 790By default, if user and password provided, OpenLDAP/WinLDAP will use basic 791authentication. On Windows you can control this behavior by providing one of 792`--basic`, `--ntlm` or `--digest` option in curl command line 793 794 curl --ntlm "ldap://user:passwd@ldap.frontec.se/o=frontec??sub?mail=*" 795 796On Windows, if no user/password specified, auto-negotiation mechanism will be 797used with current logon credentials (SSPI/SPNEGO). 798 799## Environment Variables 800 801Curl reads and understands the following environment variables: 802 803 http_proxy, HTTPS_PROXY, FTP_PROXY 804 805They should be set for protocol-specific proxies. General proxy should be set 806with 807 808 ALL_PROXY 809 810A comma-separated list of host names that shouldn't go through any proxy is 811set in (only an asterisk, `*` matches all hosts) 812 813 NO_PROXY 814 815If the host name matches one of these strings, or the host is within the 816domain of one of these strings, transactions with that node will not be 817proxied. When a domain is used, it needs to start with a period. A user can 818specify that both www.example.com and foo.example.com should not use a proxy 819by setting `NO_PROXY` to `.example.com`. By including the full name you can 820exclude specific host names, so to make `www.example.com` not use a proxy but 821still have `foo.example.com` do it, set `NO_PROXY` to `www.example.com`. 822 823The usage of the `-x`/`--proxy` flag overrides the environment variables. 824 825## Netrc 826 827Unix introduced the `.netrc` concept a long time ago. It is a way for a user 828to specify name and password for commonly visited FTP sites in a file so that 829you don't have to type them in each time you visit those sites. You realize 830this is a big security risk if someone else gets hold of your passwords, so 831therefore most unix programs won't read this file unless it is only readable 832by yourself (curl doesn't care though). 833 834Curl supports `.netrc` files if told to (using the `-n`/`--netrc` and 835`--netrc-optional` options). This is not restricted to just FTP, so curl can 836use it for all protocols where authentication is used. 837 838A very simple `.netrc` file could look something like: 839 840 machine curl.haxx.se login iamdaniel password mysecret 841 842## Custom Output 843 844To better allow script programmers to get to know about the progress of curl, 845the `-w`/`--write-out` option was introduced. Using this, you can specify what 846information from the previous transfer you want to extract. 847 848To display the amount of bytes downloaded together with some text and an 849ending newline: 850 851 curl -w 'We downloaded %{size_download} bytes\n' www.download.com 852 853## Kerberos FTP Transfer 854 855Curl supports kerberos4 and kerberos5/GSSAPI for FTP transfers. You need the 856kerberos package installed and used at curl build time for it to be available. 857 858First, get the krb-ticket the normal way, like with the kinit/kauth tool. 859Then use curl in way similar to: 860 861 curl --krb private ftp://krb4site.com -u username:fakepwd 862 863There's no use for a password on the `-u` switch, but a blank one will make 864curl ask for one and you already entered the real password to kinit/kauth. 865 866## TELNET 867 868The curl telnet support is basic and very easy to use. Curl passes all data 869passed to it on stdin to the remote server. Connect to a remote telnet server 870using a command line similar to: 871 872 curl telnet://remote.server.com 873 874And enter the data to pass to the server on stdin. The result will be sent to 875stdout or to the file you specify with `-o`. 876 877You might want the `-N`/`--no-buffer` option to switch off the buffered output 878for slow connections or similar. 879 880Pass options to the telnet protocol negotiation, by using the `-t` option. To 881tell the server we use a vt100 terminal, try something like: 882 883 curl -tTTYPE=vt100 telnet://remote.server.com 884 885Other interesting options for it `-t` include: 886 887 - `XDISPLOC=<X display>` Sets the X display location. 888 - `NEW_ENV=<var,val>` Sets an environment variable. 889 890NOTE: The telnet protocol does not specify any way to login with a specified 891user and password so curl can't do that automatically. To do that, you need to 892track when the login prompt is received and send the username and password 893accordingly. 894 895## Persistent Connections 896 897Specifying multiple files on a single command line will make curl transfer all 898of them, one after the other in the specified order. 899 900libcurl will attempt to use persistent connections for the transfers so that 901the second transfer to the same host can use the same connection that was 902already initiated and was left open in the previous transfer. This greatly 903decreases connection time for all but the first transfer and it makes a far 904better use of the network. 905 906Note that curl cannot use persistent connections for transfers that are used 907in subsequence curl invokes. Try to stuff as many URLs as possible on the same 908command line if they are using the same host, as that'll make the transfers 909faster. If you use an HTTP proxy for file transfers, practically all transfers 910will be persistent. 911 912## Multiple Transfers With A Single Command Line 913 914As is mentioned above, you can download multiple files with one command line 915by simply adding more URLs. If you want those to get saved to a local file 916instead of just printed to stdout, you need to add one save option for each 917URL you specify. Note that this also goes for the `-O` option (but not 918`--remote-name-all`). 919 920For example: get two files and use `-O` for the first and a custom file 921name for the second: 922 923 curl -O http://url.com/file.txt ftp://ftp.com/moo.exe -o moo.jpg 924 925You can also upload multiple files in a similar fashion: 926 927 curl -T local1 ftp://ftp.com/moo.exe -T local2 ftp://ftp.com/moo2.txt 928 929## IPv6 930 931curl will connect to a server with IPv6 when a host lookup returns an IPv6 932address and fall back to IPv4 if the connection fails. The `--ipv4` and 933`--ipv6` options can specify which address to use when both are 934available. IPv6 addresses can also be specified directly in URLs using the 935syntax: 936 937 http://[2001:1890:1112:1::20]/overview.html 938 939When this style is used, the `-g` option must be given to stop curl from 940interpreting the square brackets as special globbing characters. Link local 941and site local addresses including a scope identifier, such as `fe80::1234%1`, 942may also be used, but the scope portion must be numeric or match an existing 943network interface on Linux and the percent character must be URL escaped. The 944previous example in an SFTP URL might look like: 945 946 sftp://[fe80::1234%251]/ 947 948IPv6 addresses provided other than in URLs (e.g. to the `--proxy`, 949`--interface` or `--ftp-port` options) should not be URL encoded. 950 951## Metalink 952 953Curl supports Metalink (both version 3 and 4 (RFC 5854) are supported), a way 954to list multiple URIs and hashes for a file. Curl will make use of the mirrors 955listed within for failover if there are errors (such as the file or server not 956being available). It will also verify the hash of the file after the download 957completes. The Metalink file itself is downloaded and processed in memory and 958not stored in the local file system. 959 960Example to use a remote Metalink file: 961 962 curl --metalink http://www.example.com/example.metalink 963 964To use a Metalink file in the local file system, use FILE protocol 965(`file://`): 966 967 curl --metalink file://example.metalink 968 969Please note that if FILE protocol is disabled, there is no way to use a local 970Metalink file at the time of this writing. Also note that if `--metalink` and 971`--include` are used together, `--include` will be ignored. This is because 972including headers in the response will break Metalink parser and if the 973headers are included in the file described in Metalink file, hash check will 974fail. 975 976## Mailing Lists 977 978For your convenience, we have several open mailing lists to discuss curl, its 979development and things relevant to this. Get all info at 980https://curl.haxx.se/mail/. 981 982Please direct curl questions, feature requests and trouble reports to one of 983these mailing lists instead of mailing any individual. 984 985Available lists include: 986 987### curl-users 988 989Users of the command line tool. How to use it, what doesn't work, new 990features, related tools, questions, news, installations, compilations, 991running, porting etc. 992 993### curl-library 994 995Developers using or developing libcurl. Bugs, extensions, improvements. 996 997### curl-announce 998 999Low-traffic. Only receives announcements of new public versions. At worst, 1000that makes something like one or two mails per month, but usually only one 1001mail every second month. 1002 1003### curl-and-php 1004 1005Using the curl functions in PHP. Everything curl with a PHP angle. Or PHP with 1006a curl angle. 1007 1008### curl-and-python 1009 1010Python hackers using curl with or without the python binding pycurl. 1011 1012