CURL command Tutorial in Linux with Example Usage

<p>Transferring data from one place to another is one of the main task done using computers connected to a network. There are so many GUI tools out there to send and receive data, but when you are working on a console, only equipped with command line functionality, using curl is inevitable. A less known fact is that curl can work with a wide range of protocols and can solve most of your scripting tasks with ease. Before getting into details of curl use cases and examples, let’s see who is behind its development.</p> <p> </p> <p>Haxx is a team of developer consultants offering solutions to programming problems. They offer solutions in the field of Embedded programming, Unix/Linux, Network, Device Drivers, Perl scripts etc. One of the co-founder of Haxx gifted the open-source community with a tool called CURL. The man behind its development is none other than Daniel Stenberg(who is currently a Senior Network Engineer @ Mozilla.)</p> <p> </p> <p> </p> <p><strong>Reference:</strong> <a target="_blank" href="http://bit.ly/280Yz7n">Author of CURL and Libcurl</a></p> <p><strong>Reference:</strong> <a target="_blank" href="http://www.haxx.se/">Haxx Community</a></p> <p> </p> <p>CURL comes by default installed in most of the distributions. If you do not have curl tool installed, then its a single apt-get(apt-get install curl) or yum(yum install curl) command away. Installing curl will install the curl command line tool as well as libcurl library. On an Ubuntu system the package names are as follows.</p> <p> </p> <ol> <li>curl_7.22.0-3ubuntu4.7_amd64.deb</li> <li>libcurl3_7.22.0-3ubuntu4.7_amd64.deb</li> </ol> <p> </p> <h2>What is curl and what makes it a superb command line tool?</h2> <p>CURL is simply awesome because of the following reasons…</p> <ol> <li>CURL is an easy to use command line tool to send and receive files, and it supports almost all major protocols(DICT, FILE, FTP, FTPS, GOPHER, HTTP, HTTPS,  IMAP, IMAPS,  LDAP,  LDAPS,  POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP) in use.</li> <li>Can be used inside your shell scripts with ease</li> <li>Supports features like pause and resume of downloads</li> <li>It has around 120 command line options for various tasks</li> <li>It runs on all major operating systems(More than 40+ Operating systems)</li> <li>Supports cookies, forms and SSL</li> <li>Both curl command line tool and libcurl library are open source, so they can be used in any of your programs</li> <li>It supports configuration files</li> <li>Multiple upload with a single command</li> <li>Progress bar, rate limiting, and download time details</li> <li>ipv6 support</li> </ol> <p>And much more. Refer: <a target="_blank" href="http://bit.ly/1r0Pud9">http://bit.ly/1r0Pud9</a> For more feature sets and other details….</p> <h2>Basic CURL command Usage</h2> <p>Let’s get started by looking at some very basic examples of using curl in Linux. By default curl will show you the entire output on your console. A nice feature of curl is to guess the protocol based on the URL host name you use. For example if you give a URL named <em>ftp.example.com</em> (CURL will use FTP protocol to fetch data). But in case curl cannot guess the Protocol, then it will default to HTTP.</p> <p> </p> <div> <div id="highlighter_615920" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>The above command will show the entire HTTP content on that example.com URL. Here also curl tried to guess the protocol. But as it didn’t find any, it defaulted to HTTP.</p> <p> </p> <blockquote> <p>Under normal cases, you will have to specify the URI which includes the protocol information, so that curl will use your desired protocol to fetch data. For example, <em>protocol://prefix</em></p> </blockquote> <p>The previously shown example command will not save the html output(It will show you the output in the console itself.). If you want to save the output to a file, you can either use redirection method in <a href="http://bit.ly/1T1LpPV" target="_bank" itemprop="url" title="linux"><strong>linux</strong></a>, or use -o option in curl.</p> <p> </p> <div> <div id="highlighter_981170" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl example.com > example.html</code></div> <div class="line number2 index1 alt1"><code class="as3 spaces">  </code><code class="as3 plain">% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current</code></div> <div class="line number3 index2 alt2"><code class="as3 spaces">                                 </code><code class="as3 plain">Dload  Upload   Total   Spent    Left  Speed</code></div> <div class="line number4 index3 alt1"><code class="as3 value">100</code>  <code class="as3 value">1270</code>  <code class="as3 value">100</code>  <code class="as3 value">1270</code>    <code class="as3 value">0</code>     <code class="as3 value">0</code>   <code class="as3 value">2645</code>      <code class="as3 value">0</code> <code class="as3 plain">--:--:-- --:--:-- --:--:-- </code> <code class="as3 value">5852</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>The above command will save the output to example.html file. You can alternatively use -o option in curl as shown below.</p> <p> </p> <div> <div id="highlighter_353" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -o example.html example.com</code></div> <div class="line number2 index1 alt1"><code class="as3 spaces">  </code><code class="as3 plain">% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current</code></div> <div class="line number3 index2 alt2"><code class="as3 spaces">                                 </code><code class="as3 plain">Dload  Upload   Total   Spent    Left  Speed</code></div> <div class="line number4 index3 alt1"><code class="as3 value">100</code>  <code class="as3 value">1270</code>  <code class="as3 value">100</code>  <code class="as3 value">1270</code>    <code class="as3 value">0</code>     <code class="as3 value">0</code>   <code class="as3 value">2617</code>      <code class="as3 value">0</code> <code class="as3 plain">--:--:-- --:--:-- --:--:-- </code> <code class="as3 value">5799</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>Both of these methods will show you the download details like transfer rate, time, bytes etc.</p> <h3>Downloading Multiple Files using single CURL command</h3> <p> </p> <p>CURL command can be used to download multiple files at the same time, using -O option. An important fact to note here is that, curl will use the same TCP connection to download multiple files. This is done to improve the download speed. Establishing TCP connection to a target server requires multiple processes. Its called as three way handshake. To reduce the time involved in doing a three way handshake, curl will try to use the same connection for all downloads from the same server issued by the single command.</p> <p> </p> <p><strong>Related:</strong> <a target="_blank" href="http://bit.ly/280YqRB">What is TCP three-way Handshake</a></p> <p> </p> <div> <div id="highlighter_667429" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -O libiconv-</code><code class="as3 value">1.14</code><code class="as3 plain">.tar.gz http:</code><code class="as3 comments">//ftp.gnu.org/pub/gnu/libiconv/libiconv-1.10.tar.gz -O <a target="_blank" href="http://bit.ly/1r0Q3U6">http://bit.ly/1r0Q3U6</a> -O <a target="_blank" href="http://bit.ly/280YDUI">http://bit.ly/280YDUI</a></code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>The above command will download three different version of the package libiconv from <a href="http://bit.ly/1r0P5aH" target="_bank" itemprop="url" title="vsftpd-FTP Server"><strong>ftp</strong></a>.gnu.org(Please note the fact that all the three URL’s are different.). Another advantage of using <strong>-O</strong> option is that it will save the output to a file with the exact same name as the URL file name. In our example, it will save all the three files with file name as libiconv-1.10.tar.gz, libiconv-1.12.tar.gz,libiconv-1.13.tar.gz.</p> <p> </p> <h3>Following HTTP redirection Using CURL</h3> <p>Both 302 and 301 are widely accepted status codes used for HTTP redirection. 302 is normally used for temporary redirection and 301 is moved permanently. Its quite normal to encounter such URLs while using CURL. HTTP is designed to reply with a new URL, from where the client can fetch the data from.</p> <p> </p> <p>Google does this kind of redirection, if you try to do a CURL to google.com (instead of www.google.com.). The HTTP response will contain two things. It will contain the status code 301 or 302, and an alternative URL which the client can use. Web browsers will <a href="http://bit.ly/26nCuzb" target="_bank" itemprop="url" title="How to automatically water your plants with the Raspberry Pi"><strong>automatically</strong></a> redirect you to the alternative URL, when they encounter 301, or 302. But in case of curl, it will show you the exact message returned by the server. Let me show you this..</p> <p> </p> <div> <div id="highlighter_394804" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> <div class="line number5 index4 alt2">5</div> <div class="line number6 index5 alt1">6</div> <div class="line number7 index6 alt2">7</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl google.com</code></div> <div class="line number2 index1 alt1"><code class="as3 plain"><HTML><HEAD><meta http-equiv=</code><code class="as3 string">"content-type"</code> <code class="as3 plain">content=</code><code class="as3 string">"text/html;charset=utf-8"</code><code class="as3 plain">></code></div> <div class="line number3 index2 alt2"><code class="as3 plain"><TITLE></code><code class="as3 value">301</code> <code class="as3 plain">Moved</TITLE></HEAD><BODY></code></div> <div class="line number4 index3 alt1"><code class="as3 plain"><H1></code><code class="as3 value">301</code> <code class="as3 plain">Moved</H1></code></div> <div class="line number5 index4 alt2"><code class="as3 plain">The document has moved</code></div> <div class="line number6 index5 alt1"><code class="as3 plain"><A HREF=</code><code class="as3 string">"<a target="_blank" href="http://bit.ly/1r0PJox">http://bit.ly/1r0PJox</a>"</code><code class="as3 plain">>here</A>.</code></div> <div class="line number7 index6 alt2"><code class="as3 plain"></BODY></HTML></code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>If you want CURL to redirect <a href="http://bit.ly/1VNpRtY" target="_bank" itemprop="url" title="Automatically watering your plants with sensors, a Pi and webhooks"><strong>automatically</strong></a> to the new URL then you need to use the <strong>-L </strong> option as shown below.</p> <div> <div id="highlighter_366575" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -L google.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <h3>Pause/Resume Downloads using Curl Command</h3> <p> </p> <p>Similar to any GUI download manager, you can pause and resume downloads using CURL. This can be achieved using <strong>-C</strong> option as shown below. Let’s first start a download and then cancel it(with CTRL + C).</p> <p> </p> <div> <div id="highlighter_221234" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -O http:</code><code class="as3 comments">//ftp.gnu.org/pub/gnu/libiconv/libiconv-1.14.tar.gz</code></div> <div class="line number2 index1 alt1"><code class="as3 spaces">  </code><code class="as3 plain">% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current</code></div> <div class="line number3 index2 alt2"><code class="as3 spaces">                                 </code><code class="as3 plain">Dload  Upload   Total   Spent    Left  Speed</code></div> <div class="line number4 index3 alt1"><code class="as3 spaces">  </code><code class="as3 value">0</code> <code class="as3 plain">4867k   </code> <code class="as3 value">0</code>  <code class="as3 value">1196</code>    <code class="as3 value">0</code>     <code class="as3 value">0</code>   <code class="as3 value">1631</code>      <code class="as3 value">0</code>  <code class="as3 value">0</code><code class="as3 plain">:</code><code class="as3 value">50</code><code class="as3 plain">:</code><code class="as3 value">56</code> <code class="as3 plain">--:--:-- </code> <code class="as3 value">0</code><code class="as3 plain">:</code><code class="as3 value">50</code><code class="as3 plain">:</code><code class="as3 value">56</code>  <code class="as3 value">5363</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>Now let’s resume the download…</p> <p> </p> <div> <div id="highlighter_358271" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> <div class="line number5 index4 alt2">5</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -C - -O http:</code><code class="as3 comments">//ftp.gnu.org/pub/gnu/libiconv/libiconv-1.14.tar.gz</code></div> <div class="line number2 index1 alt1"><code class="as3 plain">** Resuming transfer from byte position</code> <code class="as3 value">28672</code></div> <div class="line number3 index2 alt2"><code class="as3 spaces">  </code><code class="as3 plain">% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current</code></div> <div class="line number4 index3 alt1"><code class="as3 spaces">                                 </code><code class="as3 plain">Dload  Upload   Total   Spent    Left  Speed</code></div> <div class="line number5 index4 alt2"><code class="as3 spaces">  </code><code class="as3 value">0</code> <code class="as3 plain">4839k   </code> <code class="as3 value">0</code> <code class="as3 value">30339</code>    <code class="as3 value">0</code>     <code class="as3 value">0</code>  <code class="as3 value">21558</code>      <code class="as3 value">0</code>  <code class="as3 value">0</code><code class="as3 plain">:</code><code class="as3 value">03</code><code class="as3 plain">:</code><code class="as3 value">49</code>  <code class="as3 value">0</code><code class="as3 plain">:</code><code class="as3 value">00</code><code class="as3 plain">:</code><code class="as3 value">01</code>  <code class="as3 value">0</code><code class="as3 plain">:</code><code class="as3 value">03</code><code class="as3 plain">:</code><code class="as3 value">48</code> <code class="as3 value">27185</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <blockquote> <p>On resuming the transfer, it clearly says that its resuming from byte 28672. This is because curl tried to fetch the bytes previously downloaded from the partially saved file libiconv-1.14.tar.gz, in the current directory. And on finding the partially downloaded file, it resumed from where it left last time.</p> </blockquote> <p> </p> <h3>See Complete Request And Response Headers with CURL</h3> <p> </p> <p>Commands in Linux usually comes with an option called as verbose. In verbose output, it shows you the complete information encountered by the command. Using verbose output in curl can help you see all headers (both request and response). Using Verbose is done by simply passing <strong>-v</strong></p> <p> </p> <div> <div id="highlighter_9325" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -v example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>This will show you the complete headers that curl encounters while fulfilling the request. Headers include request headers sent, Response headers received etc.</p> <p> </p> <p><strong>Related:</strong> <a target="_blank" href="http://bit.ly/1r0Pvhc">HTTP Request and Response Tutorial</a></p> <p> </p> <h3>Show only Response Headers in CURL</h3> <p> </p> <p>Sometimes you only want to see the response headers returned by the server, without seeing the actual response content. This can be used in scripts to verify the response status, response bytes, or response server type etc.</p> <p> </p> <div> <div id="highlighter_801054" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> <div class="line number5 index4 alt2">5</div> <div class="line number6 index5 alt1">6</div> <div class="line number7 index6 alt2">7</div> <div class="line number8 index7 alt1">8</div> <div class="line number9 index8 alt2">9</div> <div class="line number10 index9 alt1">10</div> <div class="line number11 index10 alt2">11</div> <div class="line number12 index11 alt1">12</div> <div class="line number13 index12 alt2">13</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -I example.com</code></div> <div class="line number2 index1 alt1"><code class="as3 plain">HTTP/</code><code class="as3 value">1.1</code> <code class="as3 value">200</code> <code class="as3 plain">OK</code></div> <div class="line number3 index2 alt2"><code class="as3 plain">Accept-Ranges: bytes</code></div> <div class="line number4 index3 alt1"><code class="as3 plain">Cache-Control: max-age=</code><code class="as3 value">604800</code></div> <div class="line number5 index4 alt2"><code class="as3 plain">Content-Type: text/html</code></div> <div class="line number6 index5 alt1"><code class="as3 keyword">Date</code><code class="as3 plain">: Mon,</code> <code class="as3 value">17</code> <code class="as3 plain">Mar</code> <code class="as3 value">2014</code> <code class="as3 value">12</code><code class="as3 plain">:</code><code class="as3 value">42</code><code class="as3 plain">:</code><code class="as3 value">14</code> <code class="as3 plain">GMT</code></div> <div class="line number7 index6 alt2"><code class="as3 plain">Etag:</code> <code class="as3 string">"359670651"</code></div> <div class="line number8 index7 alt1"><code class="as3 plain">Expires: Mon,</code> <code class="as3 value">24</code> <code class="as3 plain">Mar</code> <code class="as3 value">2014</code> <code class="as3 value">12</code><code class="as3 plain">:</code><code class="as3 value">42</code><code class="as3 plain">:</code><code class="as3 value">14</code> <code class="as3 plain">GMT</code></div> <div class="line number9 index8 alt2"><code class="as3 plain">Last-Modified: Fri,</code> <code class="as3 value">09</code> <code class="as3 plain">Aug</code> <code class="as3 value">2013</code> <code class="as3 value">23</code><code class="as3 plain">:</code><code class="as3 value">54</code><code class="as3 plain">:</code><code class="as3 value">35</code> <code class="as3 plain">GMT</code></div> <div class="line number10 index9 alt1"><code class="as3 plain">Server: ECS (iad/19AB)</code></div> <div class="line number11 index10 alt2"><code class="as3 plain">X-Cache: HIT</code></div> <div class="line number12 index11 alt1"><code class="as3 plain">x-ec-custom-error:</code> <code class="as3 value">1</code></div> <div class="line number13 index12 alt2"><code class="as3 plain">Content-Length:</code> <code class="as3 value">1270</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <h3>Use Proxy <a href="http://bit.ly/1WqNqJl" target="_bank" itemprop="url" title="Server"><strong>Server</strong></a> with CURL</h3> <p> </p> <p>If you want to send your request through a proxy server, then you can do that with <strong>-x</strong> option as shown below. Somtimes these proxy servers require authentication first. Let’s see how to perform a curl request with proxy authentication.</p> <p> </p> <div> <div id="highlighter_743504" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -x http:</code><code class="as3 comments">//proxyserver:proxyport --proxy-user user:password -L <a target="_blank" href="http://example.com/">http://example.com</a></code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>In the above command, <strong>proxyserver</strong> is your proxy server host name or ip address, <strong>proxyport</strong> is your proxy server’s port, and <strong>user:password</strong> is of course your proxy credentials. I have used -L option to follow all redirection that curl encounters(as seen before in Following HTTP redirection using CURL).</p> <p> </p> <h3>Ignore SSL Certificate Error with CURL</h3> <div class="ezAdsense adsense adsense-midtext" style="text-align:center;margin:12px;"><script async="" src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js" type="text/javascript"> </script> <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-2979805726071943" data-ad-slot="7471922310" data-ad-format="auto"></ins> <script type="text/javascript"> //<![CDATA[ (adsbygoogle = window.adsbygoogle || []).push({}); //]]> </script></div> <p> </p> <p>SSL certificates needs to be signed by an authorized certificate authority. Otherwise user agents like browser’s will warn you and requires a user action like pressing a continue button. Normally curl will not continue the connection at all, if it finds an unknown ssl certificate. Although its a nice security feature, we do configure internal self signed certificate for our internal servers. In such cases, you need to accept the unknown certificate warning and continue with the request. This can be done with curl using the <strong>-k</strong> option as shown below.</p> <p> </p> <div> <div id="highlighter_467280" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -k https:</code><code class="as3 comments">//10.1.136.101:4848</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p><strong>Related:</strong> <a target="_blank" href="http://bit.ly/1r0PYjp">How SSL Works?</a></p> <p> </p> <h3>Modify User Agent In HTTP request</h3> <p>When a web browser sends an HTTP request, it includes its own details in the request. This detail allows the server to identify the browser details. The HTTP request header that includes this information is called as <em>User-Agent</em>. Basically server’s can be configured to respond with different page layout for different user agent’s. The user agent information send by the client will be visible in server logs.</p> <p> </p> <p>A normal HTTP request send by a Firefox web browser will have a user agent that looks something like <em>“Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.9.2.3)”</em></p> <p>Using curl you can modify user agent value to your required string, as shown below.</p> <p> </p> <div> <div id="highlighter_57114" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -A</code> <code class="as3 string">"YOUR USER AGENT STRING GOES HEERE"</code> <code class="as3 plain">http:</code><code class="as3 comments">//example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <h3>Download Rate Limit with Curl</h3> <p>You can ask curl to limit download speed to your desired value. This is very helpful, when you do not want your curl command to consume much of the available bandwidth. This can be done using the below method.</p> <p> </p> <div> <div id="highlighter_270529" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl --limit-rate 100k -O http:</code><code class="as3 comments">//ftp.gnu.org/pub/gnu/libiconv/libiconv-1.10.tar.gz</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>In the above command, k stands for kilo bytes. You can also use bytes by using B, megabytes by using m, gigabytes using G.</p> <p> </p> <h3>Using CURL for FTP download and Upload</h3> <p>As discussed in the beginning of this article, CURL can work with different types of protocol. A normal use can be to upload/download files from your ftp server, without actually having any ftp client software. This can be done by passing –user argument in curl. Let’s see how to do this.</p> <h4><strong>Download File from FTP server using CURL</strong></h4> <div> <div id="highlighter_207337" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl ftp:</code><code class="as3 comments">//example.com/mydirectory/myfile.zip --user username:password -o myfile.zip</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>The above shown command will download the file myfile.zip from http://bit.ly/280YfWh, and save it as myfile.zip. But if you want to first see the directory structure of your FTP server, then you can do that by the following method.</p> <p> </p> <div> <div id="highlighter_26212" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl ftp:</code><code class="as3 comments">//example.com --user username:password</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p>Above command, will list the directory and files inside your users doc root.</p> <h4><strong>Uploading files to FTP server using CURL</strong></h4> <p>Uploading can be done using -T option in curl, and is very simple and straight forward. Its shown below.</p> <p> </p> <div> <div id="highlighter_706919" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -T myfile.zip ftp:</code><code class="as3 comments">//example.com/mydirectory/ --user username:password</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <div id="block-block-24--2" class="block block-block even"></div> <div class="block block-block even"> <h4><strong>Deleting files on FTP server</strong></h4> <p>You can also delete files on your FTP server using curl command, as shown below.</p> <div> <div id="highlighter_963548" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl ftp:</code><code class="as3 comments">//example.com/ -X 'DELE myfile.zip' --user username:password</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <h3>Sending EMAIL’s using CURL</h3> <p>If you read the list of protocol’s supported by curl, you will find SMTP as well. So curl command can be used to send email’s as well. An example is shown below.</p> <p> </p> <div> <div id="highlighter_969896" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl --url</code> <code class="as3 string">"<a href="smtps://smtp.example.com:465">smtps://smtp.example.com:465</a>"</code> <code class="as3 plain">--ssl-reqd   --mail-from</code> <code class="as3 string">"user@example.com"</code> <code class="as3 plain">--mail-rcpt</code> <code class="as3 string">"friend@example.com"</code>   <code class="as3 plain">--upload-file mailcontent.txt --user</code> <code class="as3 string">"user@example.com:password"</code> <code class="as3 plain">--insecure</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>In the above command, replace <em>smtps://smpt.example.com:465</em> with your SMTP server and port.</p> <p>–mail-from: This field contains the from address that the receiver should see.</p> <p>–mail-rcpt: This field contains TO address</p> <p>–upload-file: The file provided here should contain your message as a content</p> <p>–user: SMTP user@domain:password</p> <p>–insecure option used is exactly same as using -k option we saw earlier, to ignore unknown SSL certificates.</p> <p> </p> <h3>Using CURL to send HTTP POST, PUT, DELETE requests</h3> <p>Apart from the above seen examples, curl can be used to send different types of HTTP request methods to your server. This becomes very much handy if you want to configure an application using REST API. I will show you some example’s of sending REST API requests using CURL.</p> <p> </p> <h4><strong>Sending POST request using CURL</strong></h4> <p>If you use CURL to send request to a server without any request method option in the argument, it will by default use HTTP GET request. Which is a nice behavior. But using <strong>-X</strong> option in curl, you can send your required HTTP method to the server. Let’s see POST request.</p> <p> </p> <div> <div id="highlighter_49310" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">$curl -X POST -u  admin:admin http:</code><code class="as3 comments">//example.com/myconfigs/status -Hcontent-type:application/xml -d @/home/user/file.xml</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>In the above example, PUT is the request method, <strong>-u</strong> is used to mention credentials to access that specific resource on the server, -H <strong>content-type</strong> is the type of content format that we will be sending to the server (can be xml, normal text etc). <strong>-d</strong> with @/home/user/file.xml indicates to send the content of file.xml to the server. This file will contain the configuration options with correct syntax that the URL <strong>http://bit.ly/1r0Pr0Q</strong> will accept.</p> <p> </p> <p>Sending PUT request is exactly same as the above shown example of POST. Simply replace POST with PUT in the above example. If your web server does not accept these methods, you will get a 405 error as reply. HTTP 405 means that the server does not accept the HTTP method on that specific URL.</p> <p> </p> <p>You can also get <em>HTTP unsupported Media Type</em> error as reply, if the server does not accept application/xml format. The HTTP status code for unsupported media type is 415.</p> <p> </p> <h3>Sending Cookies to Server using CURL</h3> <p> </p> <p>CURL can be used to send requests to the server using a previously got cookie. You can either use VALUE=DATA format or give a file name as parameter, so that curl can use cookie data from the file as input. You can also save the cookies you get from the server to a file using <strong>-c</strong> option as shown below.</p> <p> </p> <div> <div id="highlighter_688462" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -b mycookies.txt http:</code><code class="as3 comments">//example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>Using the above command, you can send cookies saved in the file (<em>mycookies.txt</em> in our case) as input to the server. Alternatively you can also use the below method to send cookies.</p> <p> </p> <div> <div id="highlighter_745070" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -b</code> <code class="as3 string">"name=value"</code> <code class="as3 plain">http:</code><code class="as3 comments">//example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>If there is no = sign in the parameter passed to <strong>-b</strong> switch, then it is considered as a file, from where cookies should be read as input(basically the previous method we saw)</p> <p> </p> <h3>Sending Your own HTTP headers using CURL</h3> <p>HTTP headers contain details so that that the server and the client can understand each other in a much better way. Headers contain too many information. Some of them are mentioned below. Please note that we already did see one header modfication with curl, while we modified <strong>user-agent</strong>.</p> <p> </p> <div> <div id="highlighter_748813" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> <div class="line number5 index4 alt2">5</div> <div class="line number6 index5 alt1">6</div> <div class="line number7 index6 alt2">7</div> <div class="line number8 index7 alt1">8</div> <div class="line number9 index8 alt2">9</div> <div class="line number10 index9 alt1">10</div> <div class="line number11 index10 alt2">11</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">Accept-Ranges: bytes</code></div> <div class="line number2 index1 alt1"><code class="as3 plain">Cache-Control: max-age=</code><code class="as3 value">604800</code></div> <div class="line number3 index2 alt2"><code class="as3 plain">Content-Type: text/html</code></div> <div class="line number4 index3 alt1"><code class="as3 keyword">Date</code><code class="as3 plain">: Tue,</code> <code class="as3 value">18</code> <code class="as3 plain">Mar</code> <code class="as3 value">2014</code> <code class="as3 value">15</code><code class="as3 plain">:</code><code class="as3 value">42</code><code class="as3 plain">:</code><code class="as3 value">32</code> <code class="as3 plain">GMT</code></div> <div class="line number5 index4 alt2"><code class="as3 plain">Etag:</code> <code class="as3 string">"359670651"</code></div> <div class="line number6 index5 alt1"><code class="as3 plain">Expires: Tue,</code> <code class="as3 value">25</code> <code class="as3 plain">Mar</code> <code class="as3 value">2014</code> <code class="as3 value">15</code><code class="as3 plain">:</code><code class="as3 value">42</code><code class="as3 plain">:</code><code class="as3 value">32</code> <code class="as3 plain">GMT</code></div> <div class="line number7 index6 alt2"><code class="as3 plain">Last-Modified: Fri,</code> <code class="as3 value">09</code> <code class="as3 plain">Aug</code> <code class="as3 value">2013</code> <code class="as3 value">23</code><code class="as3 plain">:</code><code class="as3 value">54</code><code class="as3 plain">:</code><code class="as3 value">35</code> <code class="as3 plain">GMT</code></div> <div class="line number8 index7 alt1"><code class="as3 plain">Server: ECS (iad/19AB)</code></div> <div class="line number9 index8 alt2"><code class="as3 plain">X-Cache: HIT</code></div> <div class="line number10 index9 alt1"><code class="as3 plain">x-ec-custom-error:</code> <code class="as3 value">1</code></div> <div class="line number11 index10 alt2"><code class="as3 plain">Content-Length:</code> <code class="as3 value">1270</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>All of the above shown stuff returned by a server are part of HTTP headers. You can modify the HTTP request headers using CURL. Although whether its a good feature of bad requires a serious debate, coz modifying headers can fool a web server receiving the request. Due to this the data found in headers can never be trusted. Let’s see how to modify headers while sending request.</p> <p> </p> <p><strong>-H</strong> option in curl can be used to modify headers. You can modify any header of your wish. For example, let’s modify our Accept and Content-type headers in the request.</p> <p> </p> <div> <div id="highlighter_121929" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -H</code> <code class="as3 string">"Accept: application/xml"</code> <code class="as3 plain">-H</code> <code class="as3 string">"Content-Type: application/xml"</code> <code class="as3 plain">http:</code><code class="as3 comments">//example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <h3>Verifying SSL certificates using CURL</h3> <p> </p> <p>We saw the method to ignore the SSL certificate verification with <strong>-k</strong> option. But what if you want to verify the certificate the server is replying with. In that case, you need to provide the CA (Certificate Authority Certificate) to curl. This can be done by a simple command line option called <strong>–cacert</strong>.</p> <p> </p> <div> <div id="highlighter_919462" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl --cacert my-ca.crt https:</code><code class="as3 comments">//example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <h3>Download a file depending upon file modification time</h3> <p> </p> <p>At times, you only want to download a document from a URL if it is modified after your specified time. This is very handy option in curl. Its done by <strong>-z</strong> option in curl as shown below.</p> <p> </p> <div> <div id="highlighter_72147" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -z</code> <code class="as3 value">3</code><code class="as3 plain">-Jan-</code><code class="as3 value">14</code> <code class="as3 plain">http:</code><code class="as3 comments">//example.com/myfile.gz</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>The above command will download the file myfile.gz, if its modified after 3rd jan 2014. 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CURL command Tutorial in Linux with Example Usage

Transferring data from one place to another is one of the main task done using computers connected to a network. There are so many GUI tools out there to send and receive data, but when you are workin…

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CURL command Tutorial in Linux with Example Usage

<p>Transferring data from one place to another is one of the main task done using computers connected to a network. There are so many GUI tools out there to send and receive data, but when you are working on a console, only equipped with command line functionality, using curl is inevitable. A less known fact is that curl can work with a wide range of protocols and can solve most of your scripting tasks with ease. Before getting into details of curl use cases and examples, let’s see who is behind its development.</p> <p> </p> <p>Haxx is a team of developer consultants offering solutions to programming problems. They offer solutions in the field of Embedded programming, Unix/Linux, Network, Device Drivers, Perl scripts etc. One of the co-founder of Haxx gifted the open-source community with a tool called CURL. The man behind its development is none other than Daniel Stenberg(who is currently a Senior Network Engineer @ Mozilla.)</p> <p> </p> <p> </p> <p><strong>Reference:</strong> <a target="_blank" href="http://bit.ly/280Yz7n">Author of CURL and Libcurl</a></p> <p><strong>Reference:</strong> <a target="_blank" href="http://www.haxx.se/">Haxx Community</a></p> <p> </p> <p>CURL comes by default installed in most of the distributions. If you do not have curl tool installed, then its a single apt-get(apt-get install curl) or yum(yum install curl) command away. Installing curl will install the curl command line tool as well as libcurl library. On an Ubuntu system the package names are as follows.</p> <p> </p> <ol> <li>curl_7.22.0-3ubuntu4.7_amd64.deb</li> <li>libcurl3_7.22.0-3ubuntu4.7_amd64.deb</li> </ol> <p> </p> <h2>What is curl and what makes it a superb command line tool?</h2> <p>CURL is simply awesome because of the following reasons…</p> <ol> <li>CURL is an easy to use command line tool to send and receive files, and it supports almost all major protocols(DICT, FILE, FTP, FTPS, GOPHER, HTTP, HTTPS,  IMAP, IMAPS,  LDAP,  LDAPS,  POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP) in use.</li> <li>Can be used inside your shell scripts with ease</li> <li>Supports features like pause and resume of downloads</li> <li>It has around 120 command line options for various tasks</li> <li>It runs on all major operating systems(More than 40+ Operating systems)</li> <li>Supports cookies, forms and SSL</li> <li>Both curl command line tool and libcurl library are open source, so they can be used in any of your programs</li> <li>It supports configuration files</li> <li>Multiple upload with a single command</li> <li>Progress bar, rate limiting, and download time details</li> <li>ipv6 support</li> </ol> <p>And much more. Refer: <a target="_blank" href="http://bit.ly/1r0Pud9">http://bit.ly/1r0Pud9</a> For more feature sets and other details….</p> <h2>Basic CURL command Usage</h2> <p>Let’s get started by looking at some very basic examples of using curl in Linux. By default curl will show you the entire output on your console. A nice feature of curl is to guess the protocol based on the URL host name you use. For example if you give a URL named <em>ftp.example.com</em> (CURL will use FTP protocol to fetch data). But in case curl cannot guess the Protocol, then it will default to HTTP.</p> <p> </p> <div> <div id="highlighter_615920" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>The above command will show the entire HTTP content on that example.com URL. Here also curl tried to guess the protocol. But as it didn’t find any, it defaulted to HTTP.</p> <p> </p> <blockquote> <p>Under normal cases, you will have to specify the URI which includes the protocol information, so that curl will use your desired protocol to fetch data. For example, <em>protocol://prefix</em></p> </blockquote> <p>The previously shown example command will not save the html output(It will show you the output in the console itself.). If you want to save the output to a file, you can either use redirection method in <a href="http://bit.ly/1T1LpPV" target="_bank" itemprop="url" title="linux"><strong>linux</strong></a>, or use -o option in curl.</p> <p> </p> <div> <div id="highlighter_981170" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl example.com > example.html</code></div> <div class="line number2 index1 alt1"><code class="as3 spaces">  </code><code class="as3 plain">% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current</code></div> <div class="line number3 index2 alt2"><code class="as3 spaces">                                 </code><code class="as3 plain">Dload  Upload   Total   Spent    Left  Speed</code></div> <div class="line number4 index3 alt1"><code class="as3 value">100</code>  <code class="as3 value">1270</code>  <code class="as3 value">100</code>  <code class="as3 value">1270</code>    <code class="as3 value">0</code>     <code class="as3 value">0</code>   <code class="as3 value">2645</code>      <code class="as3 value">0</code> <code class="as3 plain">--:--:-- --:--:-- --:--:-- </code> <code class="as3 value">5852</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>The above command will save the output to example.html file. You can alternatively use -o option in curl as shown below.</p> <p> </p> <div> <div id="highlighter_353" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -o example.html example.com</code></div> <div class="line number2 index1 alt1"><code class="as3 spaces">  </code><code class="as3 plain">% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current</code></div> <div class="line number3 index2 alt2"><code class="as3 spaces">                                 </code><code class="as3 plain">Dload  Upload   Total   Spent    Left  Speed</code></div> <div class="line number4 index3 alt1"><code class="as3 value">100</code>  <code class="as3 value">1270</code>  <code class="as3 value">100</code>  <code class="as3 value">1270</code>    <code class="as3 value">0</code>     <code class="as3 value">0</code>   <code class="as3 value">2617</code>      <code class="as3 value">0</code> <code class="as3 plain">--:--:-- --:--:-- --:--:-- </code> <code class="as3 value">5799</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>Both of these methods will show you the download details like transfer rate, time, bytes etc.</p> <h3>Downloading Multiple Files using single CURL command</h3> <p> </p> <p>CURL command can be used to download multiple files at the same time, using -O option. An important fact to note here is that, curl will use the same TCP connection to download multiple files. This is done to improve the download speed. Establishing TCP connection to a target server requires multiple processes. Its called as three way handshake. To reduce the time involved in doing a three way handshake, curl will try to use the same connection for all downloads from the same server issued by the single command.</p> <p> </p> <p><strong>Related:</strong> <a target="_blank" href="http://bit.ly/280YqRB">What is TCP three-way Handshake</a></p> <p> </p> <div> <div id="highlighter_667429" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -O libiconv-</code><code class="as3 value">1.14</code><code class="as3 plain">.tar.gz http:</code><code class="as3 comments">//ftp.gnu.org/pub/gnu/libiconv/libiconv-1.10.tar.gz -O <a target="_blank" href="http://bit.ly/1r0Q3U6">http://bit.ly/1r0Q3U6</a> -O <a target="_blank" href="http://bit.ly/280YDUI">http://bit.ly/280YDUI</a></code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>The above command will download three different version of the package libiconv from <a href="http://bit.ly/1r0P5aH" target="_bank" itemprop="url" title="vsftpd-FTP Server"><strong>ftp</strong></a>.gnu.org(Please note the fact that all the three URL’s are different.). Another advantage of using <strong>-O</strong> option is that it will save the output to a file with the exact same name as the URL file name. In our example, it will save all the three files with file name as libiconv-1.10.tar.gz, libiconv-1.12.tar.gz,libiconv-1.13.tar.gz.</p> <p> </p> <h3>Following HTTP redirection Using CURL</h3> <p>Both 302 and 301 are widely accepted status codes used for HTTP redirection. 302 is normally used for temporary redirection and 301 is moved permanently. Its quite normal to encounter such URLs while using CURL. HTTP is designed to reply with a new URL, from where the client can fetch the data from.</p> <p> </p> <p>Google does this kind of redirection, if you try to do a CURL to google.com (instead of www.google.com.). The HTTP response will contain two things. It will contain the status code 301 or 302, and an alternative URL which the client can use. Web browsers will <a href="http://bit.ly/26nCuzb" target="_bank" itemprop="url" title="How to automatically water your plants with the Raspberry Pi"><strong>automatically</strong></a> redirect you to the alternative URL, when they encounter 301, or 302. But in case of curl, it will show you the exact message returned by the server. Let me show you this..</p> <p> </p> <div> <div id="highlighter_394804" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> <div class="line number5 index4 alt2">5</div> <div class="line number6 index5 alt1">6</div> <div class="line number7 index6 alt2">7</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl google.com</code></div> <div class="line number2 index1 alt1"><code class="as3 plain"><HTML><HEAD><meta http-equiv=</code><code class="as3 string">"content-type"</code> <code class="as3 plain">content=</code><code class="as3 string">"text/html;charset=utf-8"</code><code class="as3 plain">></code></div> <div class="line number3 index2 alt2"><code class="as3 plain"><TITLE></code><code class="as3 value">301</code> <code class="as3 plain">Moved</TITLE></HEAD><BODY></code></div> <div class="line number4 index3 alt1"><code class="as3 plain"><H1></code><code class="as3 value">301</code> <code class="as3 plain">Moved</H1></code></div> <div class="line number5 index4 alt2"><code class="as3 plain">The document has moved</code></div> <div class="line number6 index5 alt1"><code class="as3 plain"><A HREF=</code><code class="as3 string">"<a target="_blank" href="http://bit.ly/1r0PJox">http://bit.ly/1r0PJox</a>"</code><code class="as3 plain">>here</A>.</code></div> <div class="line number7 index6 alt2"><code class="as3 plain"></BODY></HTML></code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>If you want CURL to redirect <a href="http://bit.ly/1VNpRtY" target="_bank" itemprop="url" title="Automatically watering your plants with sensors, a Pi and webhooks"><strong>automatically</strong></a> to the new URL then you need to use the <strong>-L </strong> option as shown below.</p> <div> <div id="highlighter_366575" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -L google.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <h3>Pause/Resume Downloads using Curl Command</h3> <p> </p> <p>Similar to any GUI download manager, you can pause and resume downloads using CURL. This can be achieved using <strong>-C</strong> option as shown below. Let’s first start a download and then cancel it(with CTRL + C).</p> <p> </p> <div> <div id="highlighter_221234" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -O http:</code><code class="as3 comments">//ftp.gnu.org/pub/gnu/libiconv/libiconv-1.14.tar.gz</code></div> <div class="line number2 index1 alt1"><code class="as3 spaces">  </code><code class="as3 plain">% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current</code></div> <div class="line number3 index2 alt2"><code class="as3 spaces">                                 </code><code class="as3 plain">Dload  Upload   Total   Spent    Left  Speed</code></div> <div class="line number4 index3 alt1"><code class="as3 spaces">  </code><code class="as3 value">0</code> <code class="as3 plain">4867k   </code> <code class="as3 value">0</code>  <code class="as3 value">1196</code>    <code class="as3 value">0</code>     <code class="as3 value">0</code>   <code class="as3 value">1631</code>      <code class="as3 value">0</code>  <code class="as3 value">0</code><code class="as3 plain">:</code><code class="as3 value">50</code><code class="as3 plain">:</code><code class="as3 value">56</code> <code class="as3 plain">--:--:-- </code> <code class="as3 value">0</code><code class="as3 plain">:</code><code class="as3 value">50</code><code class="as3 plain">:</code><code class="as3 value">56</code>  <code class="as3 value">5363</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>Now let’s resume the download…</p> <p> </p> <div> <div id="highlighter_358271" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> <div class="line number5 index4 alt2">5</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -C - -O http:</code><code class="as3 comments">//ftp.gnu.org/pub/gnu/libiconv/libiconv-1.14.tar.gz</code></div> <div class="line number2 index1 alt1"><code class="as3 plain">** Resuming transfer from byte position</code> <code class="as3 value">28672</code></div> <div class="line number3 index2 alt2"><code class="as3 spaces">  </code><code class="as3 plain">% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current</code></div> <div class="line number4 index3 alt1"><code class="as3 spaces">                                 </code><code class="as3 plain">Dload  Upload   Total   Spent    Left  Speed</code></div> <div class="line number5 index4 alt2"><code class="as3 spaces">  </code><code class="as3 value">0</code> <code class="as3 plain">4839k   </code> <code class="as3 value">0</code> <code class="as3 value">30339</code>    <code class="as3 value">0</code>     <code class="as3 value">0</code>  <code class="as3 value">21558</code>      <code class="as3 value">0</code>  <code class="as3 value">0</code><code class="as3 plain">:</code><code class="as3 value">03</code><code class="as3 plain">:</code><code class="as3 value">49</code>  <code class="as3 value">0</code><code class="as3 plain">:</code><code class="as3 value">00</code><code class="as3 plain">:</code><code class="as3 value">01</code>  <code class="as3 value">0</code><code class="as3 plain">:</code><code class="as3 value">03</code><code class="as3 plain">:</code><code class="as3 value">48</code> <code class="as3 value">27185</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <blockquote> <p>On resuming the transfer, it clearly says that its resuming from byte 28672. This is because curl tried to fetch the bytes previously downloaded from the partially saved file libiconv-1.14.tar.gz, in the current directory. And on finding the partially downloaded file, it resumed from where it left last time.</p> </blockquote> <p> </p> <h3>See Complete Request And Response Headers with CURL</h3> <p> </p> <p>Commands in Linux usually comes with an option called as verbose. In verbose output, it shows you the complete information encountered by the command. Using verbose output in curl can help you see all headers (both request and response). Using Verbose is done by simply passing <strong>-v</strong></p> <p> </p> <div> <div id="highlighter_9325" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -v example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>This will show you the complete headers that curl encounters while fulfilling the request. Headers include request headers sent, Response headers received etc.</p> <p> </p> <p><strong>Related:</strong> <a target="_blank" href="http://bit.ly/1r0Pvhc">HTTP Request and Response Tutorial</a></p> <p> </p> <h3>Show only Response Headers in CURL</h3> <p> </p> <p>Sometimes you only want to see the response headers returned by the server, without seeing the actual response content. This can be used in scripts to verify the response status, response bytes, or response server type etc.</p> <p> </p> <div> <div id="highlighter_801054" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> <div class="line number5 index4 alt2">5</div> <div class="line number6 index5 alt1">6</div> <div class="line number7 index6 alt2">7</div> <div class="line number8 index7 alt1">8</div> <div class="line number9 index8 alt2">9</div> <div class="line number10 index9 alt1">10</div> <div class="line number11 index10 alt2">11</div> <div class="line number12 index11 alt1">12</div> <div class="line number13 index12 alt2">13</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -I example.com</code></div> <div class="line number2 index1 alt1"><code class="as3 plain">HTTP/</code><code class="as3 value">1.1</code> <code class="as3 value">200</code> <code class="as3 plain">OK</code></div> <div class="line number3 index2 alt2"><code class="as3 plain">Accept-Ranges: bytes</code></div> <div class="line number4 index3 alt1"><code class="as3 plain">Cache-Control: max-age=</code><code class="as3 value">604800</code></div> <div class="line number5 index4 alt2"><code class="as3 plain">Content-Type: text/html</code></div> <div class="line number6 index5 alt1"><code class="as3 keyword">Date</code><code class="as3 plain">: Mon,</code> <code class="as3 value">17</code> <code class="as3 plain">Mar</code> <code class="as3 value">2014</code> <code class="as3 value">12</code><code class="as3 plain">:</code><code class="as3 value">42</code><code class="as3 plain">:</code><code class="as3 value">14</code> <code class="as3 plain">GMT</code></div> <div class="line number7 index6 alt2"><code class="as3 plain">Etag:</code> <code class="as3 string">"359670651"</code></div> <div class="line number8 index7 alt1"><code class="as3 plain">Expires: Mon,</code> <code class="as3 value">24</code> <code class="as3 plain">Mar</code> <code class="as3 value">2014</code> <code class="as3 value">12</code><code class="as3 plain">:</code><code class="as3 value">42</code><code class="as3 plain">:</code><code class="as3 value">14</code> <code class="as3 plain">GMT</code></div> <div class="line number9 index8 alt2"><code class="as3 plain">Last-Modified: Fri,</code> <code class="as3 value">09</code> <code class="as3 plain">Aug</code> <code class="as3 value">2013</code> <code class="as3 value">23</code><code class="as3 plain">:</code><code class="as3 value">54</code><code class="as3 plain">:</code><code class="as3 value">35</code> <code class="as3 plain">GMT</code></div> <div class="line number10 index9 alt1"><code class="as3 plain">Server: ECS (iad/19AB)</code></div> <div class="line number11 index10 alt2"><code class="as3 plain">X-Cache: HIT</code></div> <div class="line number12 index11 alt1"><code class="as3 plain">x-ec-custom-error:</code> <code class="as3 value">1</code></div> <div class="line number13 index12 alt2"><code class="as3 plain">Content-Length:</code> <code class="as3 value">1270</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <h3>Use Proxy <a href="http://bit.ly/1WqNqJl" target="_bank" itemprop="url" title="Server"><strong>Server</strong></a> with CURL</h3> <p> </p> <p>If you want to send your request through a proxy server, then you can do that with <strong>-x</strong> option as shown below. Somtimes these proxy servers require authentication first. Let’s see how to perform a curl request with proxy authentication.</p> <p> </p> <div> <div id="highlighter_743504" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -x http:</code><code class="as3 comments">//proxyserver:proxyport --proxy-user user:password -L <a target="_blank" href="http://example.com/">http://example.com</a></code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>In the above command, <strong>proxyserver</strong> is your proxy server host name or ip address, <strong>proxyport</strong> is your proxy server’s port, and <strong>user:password</strong> is of course your proxy credentials. I have used -L option to follow all redirection that curl encounters(as seen before in Following HTTP redirection using CURL).</p> <p> </p> <h3>Ignore SSL Certificate Error with CURL</h3> <div class="ezAdsense adsense adsense-midtext" style="text-align:center;margin:12px;"><script async="" src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js" type="text/javascript"> </script> <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-2979805726071943" data-ad-slot="7471922310" data-ad-format="auto"></ins> <script type="text/javascript"> //<![CDATA[ (adsbygoogle = window.adsbygoogle || []).push({}); //]]> </script></div> <p> </p> <p>SSL certificates needs to be signed by an authorized certificate authority. Otherwise user agents like browser’s will warn you and requires a user action like pressing a continue button. Normally curl will not continue the connection at all, if it finds an unknown ssl certificate. Although its a nice security feature, we do configure internal self signed certificate for our internal servers. In such cases, you need to accept the unknown certificate warning and continue with the request. This can be done with curl using the <strong>-k</strong> option as shown below.</p> <p> </p> <div> <div id="highlighter_467280" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -k https:</code><code class="as3 comments">//10.1.136.101:4848</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p><strong>Related:</strong> <a target="_blank" href="http://bit.ly/1r0PYjp">How SSL Works?</a></p> <p> </p> <h3>Modify User Agent In HTTP request</h3> <p>When a web browser sends an HTTP request, it includes its own details in the request. This detail allows the server to identify the browser details. The HTTP request header that includes this information is called as <em>User-Agent</em>. Basically server’s can be configured to respond with different page layout for different user agent’s. The user agent information send by the client will be visible in server logs.</p> <p> </p> <p>A normal HTTP request send by a Firefox web browser will have a user agent that looks something like <em>“Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.9.2.3)”</em></p> <p>Using curl you can modify user agent value to your required string, as shown below.</p> <p> </p> <div> <div id="highlighter_57114" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -A</code> <code class="as3 string">"YOUR USER AGENT STRING GOES HEERE"</code> <code class="as3 plain">http:</code><code class="as3 comments">//example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <h3>Download Rate Limit with Curl</h3> <p>You can ask curl to limit download speed to your desired value. This is very helpful, when you do not want your curl command to consume much of the available bandwidth. This can be done using the below method.</p> <p> </p> <div> <div id="highlighter_270529" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl --limit-rate 100k -O http:</code><code class="as3 comments">//ftp.gnu.org/pub/gnu/libiconv/libiconv-1.10.tar.gz</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>In the above command, k stands for kilo bytes. You can also use bytes by using B, megabytes by using m, gigabytes using G.</p> <p> </p> <h3>Using CURL for FTP download and Upload</h3> <p>As discussed in the beginning of this article, CURL can work with different types of protocol. A normal use can be to upload/download files from your ftp server, without actually having any ftp client software. This can be done by passing –user argument in curl. Let’s see how to do this.</p> <h4><strong>Download File from FTP server using CURL</strong></h4> <div> <div id="highlighter_207337" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl ftp:</code><code class="as3 comments">//example.com/mydirectory/myfile.zip --user username:password -o myfile.zip</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>The above shown command will download the file myfile.zip from http://bit.ly/280YfWh, and save it as myfile.zip. But if you want to first see the directory structure of your FTP server, then you can do that by the following method.</p> <p> </p> <div> <div id="highlighter_26212" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl ftp:</code><code class="as3 comments">//example.com --user username:password</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p>Above command, will list the directory and files inside your users doc root.</p> <h4><strong>Uploading files to FTP server using CURL</strong></h4> <p>Uploading can be done using -T option in curl, and is very simple and straight forward. Its shown below.</p> <p> </p> <div> <div id="highlighter_706919" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -T myfile.zip ftp:</code><code class="as3 comments">//example.com/mydirectory/ --user username:password</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <div id="block-block-24--2" class="block block-block even"></div> <div class="block block-block even"> <h4><strong>Deleting files on FTP server</strong></h4> <p>You can also delete files on your FTP server using curl command, as shown below.</p> <div> <div id="highlighter_963548" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl ftp:</code><code class="as3 comments">//example.com/ -X 'DELE myfile.zip' --user username:password</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <h3>Sending EMAIL’s using CURL</h3> <p>If you read the list of protocol’s supported by curl, you will find SMTP as well. So curl command can be used to send email’s as well. An example is shown below.</p> <p> </p> <div> <div id="highlighter_969896" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl --url</code> <code class="as3 string">"<a href="smtps://smtp.example.com:465">smtps://smtp.example.com:465</a>"</code> <code class="as3 plain">--ssl-reqd   --mail-from</code> <code class="as3 string">"user@example.com"</code> <code class="as3 plain">--mail-rcpt</code> <code class="as3 string">"friend@example.com"</code>   <code class="as3 plain">--upload-file mailcontent.txt --user</code> <code class="as3 string">"user@example.com:password"</code> <code class="as3 plain">--insecure</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>In the above command, replace <em>smtps://smpt.example.com:465</em> with your SMTP server and port.</p> <p>–mail-from: This field contains the from address that the receiver should see.</p> <p>–mail-rcpt: This field contains TO address</p> <p>–upload-file: The file provided here should contain your message as a content</p> <p>–user: SMTP user@domain:password</p> <p>–insecure option used is exactly same as using -k option we saw earlier, to ignore unknown SSL certificates.</p> <p> </p> <h3>Using CURL to send HTTP POST, PUT, DELETE requests</h3> <p>Apart from the above seen examples, curl can be used to send different types of HTTP request methods to your server. This becomes very much handy if you want to configure an application using REST API. I will show you some example’s of sending REST API requests using CURL.</p> <p> </p> <h4><strong>Sending POST request using CURL</strong></h4> <p>If you use CURL to send request to a server without any request method option in the argument, it will by default use HTTP GET request. Which is a nice behavior. But using <strong>-X</strong> option in curl, you can send your required HTTP method to the server. Let’s see POST request.</p> <p> </p> <div> <div id="highlighter_49310" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">$curl -X POST -u  admin:admin http:</code><code class="as3 comments">//example.com/myconfigs/status -Hcontent-type:application/xml -d @/home/user/file.xml</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>In the above example, PUT is the request method, <strong>-u</strong> is used to mention credentials to access that specific resource on the server, -H <strong>content-type</strong> is the type of content format that we will be sending to the server (can be xml, normal text etc). <strong>-d</strong> with @/home/user/file.xml indicates to send the content of file.xml to the server. This file will contain the configuration options with correct syntax that the URL <strong>http://bit.ly/1r0Pr0Q</strong> will accept.</p> <p> </p> <p>Sending PUT request is exactly same as the above shown example of POST. Simply replace POST with PUT in the above example. If your web server does not accept these methods, you will get a 405 error as reply. HTTP 405 means that the server does not accept the HTTP method on that specific URL.</p> <p> </p> <p>You can also get <em>HTTP unsupported Media Type</em> error as reply, if the server does not accept application/xml format. The HTTP status code for unsupported media type is 415.</p> <p> </p> <h3>Sending Cookies to Server using CURL</h3> <p> </p> <p>CURL can be used to send requests to the server using a previously got cookie. You can either use VALUE=DATA format or give a file name as parameter, so that curl can use cookie data from the file as input. You can also save the cookies you get from the server to a file using <strong>-c</strong> option as shown below.</p> <p> </p> <div> <div id="highlighter_688462" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -b mycookies.txt http:</code><code class="as3 comments">//example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p> </p> <p>Using the above command, you can send cookies saved in the file (<em>mycookies.txt</em> in our case) as input to the server. Alternatively you can also use the below method to send cookies.</p> <p> </p> <div> <div id="highlighter_745070" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -b</code> <code class="as3 string">"name=value"</code> <code class="as3 plain">http:</code><code class="as3 comments">//example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>If there is no = sign in the parameter passed to <strong>-b</strong> switch, then it is considered as a file, from where cookies should be read as input(basically the previous method we saw)</p> <p> </p> <h3>Sending Your own HTTP headers using CURL</h3> <p>HTTP headers contain details so that that the server and the client can understand each other in a much better way. Headers contain too many information. Some of them are mentioned below. Please note that we already did see one header modfication with curl, while we modified <strong>user-agent</strong>.</p> <p> </p> <div> <div id="highlighter_748813" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> <div class="line number2 index1 alt1">2</div> <div class="line number3 index2 alt2">3</div> <div class="line number4 index3 alt1">4</div> <div class="line number5 index4 alt2">5</div> <div class="line number6 index5 alt1">6</div> <div class="line number7 index6 alt2">7</div> <div class="line number8 index7 alt1">8</div> <div class="line number9 index8 alt2">9</div> <div class="line number10 index9 alt1">10</div> <div class="line number11 index10 alt2">11</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">Accept-Ranges: bytes</code></div> <div class="line number2 index1 alt1"><code class="as3 plain">Cache-Control: max-age=</code><code class="as3 value">604800</code></div> <div class="line number3 index2 alt2"><code class="as3 plain">Content-Type: text/html</code></div> <div class="line number4 index3 alt1"><code class="as3 keyword">Date</code><code class="as3 plain">: Tue,</code> <code class="as3 value">18</code> <code class="as3 plain">Mar</code> <code class="as3 value">2014</code> <code class="as3 value">15</code><code class="as3 plain">:</code><code class="as3 value">42</code><code class="as3 plain">:</code><code class="as3 value">32</code> <code class="as3 plain">GMT</code></div> <div class="line number5 index4 alt2"><code class="as3 plain">Etag:</code> <code class="as3 string">"359670651"</code></div> <div class="line number6 index5 alt1"><code class="as3 plain">Expires: Tue,</code> <code class="as3 value">25</code> <code class="as3 plain">Mar</code> <code class="as3 value">2014</code> <code class="as3 value">15</code><code class="as3 plain">:</code><code class="as3 value">42</code><code class="as3 plain">:</code><code class="as3 value">32</code> <code class="as3 plain">GMT</code></div> <div class="line number7 index6 alt2"><code class="as3 plain">Last-Modified: Fri,</code> <code class="as3 value">09</code> <code class="as3 plain">Aug</code> <code class="as3 value">2013</code> <code class="as3 value">23</code><code class="as3 plain">:</code><code class="as3 value">54</code><code class="as3 plain">:</code><code class="as3 value">35</code> <code class="as3 plain">GMT</code></div> <div class="line number8 index7 alt1"><code class="as3 plain">Server: ECS (iad/19AB)</code></div> <div class="line number9 index8 alt2"><code class="as3 plain">X-Cache: HIT</code></div> <div class="line number10 index9 alt1"><code class="as3 plain">x-ec-custom-error:</code> <code class="as3 value">1</code></div> <div class="line number11 index10 alt2"><code class="as3 plain">Content-Length:</code> <code class="as3 value">1270</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>All of the above shown stuff returned by a server are part of HTTP headers. You can modify the HTTP request headers using CURL. Although whether its a good feature of bad requires a serious debate, coz modifying headers can fool a web server receiving the request. Due to this the data found in headers can never be trusted. Let’s see how to modify headers while sending request.</p> <p> </p> <p><strong>-H</strong> option in curl can be used to modify headers. You can modify any header of your wish. For example, let’s modify our Accept and Content-type headers in the request.</p> <p> </p> <div> <div id="highlighter_121929" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -H</code> <code class="as3 string">"Accept: application/xml"</code> <code class="as3 plain">-H</code> <code class="as3 string">"Content-Type: application/xml"</code> <code class="as3 plain">http:</code><code class="as3 comments">//example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <h3>Verifying SSL certificates using CURL</h3> <p> </p> <p>We saw the method to ignore the SSL certificate verification with <strong>-k</strong> option. But what if you want to verify the certificate the server is replying with. In that case, you need to provide the CA (Certificate Authority Certificate) to curl. This can be done by a simple command line option called <strong>–cacert</strong>.</p> <p> </p> <div> <div id="highlighter_919462" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl --cacert my-ca.crt https:</code><code class="as3 comments">//example.com</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <h3>Download a file depending upon file modification time</h3> <p> </p> <p>At times, you only want to download a document from a URL if it is modified after your specified time. This is very handy option in curl. Its done by <strong>-z</strong> option in curl as shown below.</p> <p> </p> <div> <div id="highlighter_72147" class="syntaxhighlighter as3"> <div class="toolbar"><a target="_blank" class="toolbar_item command_help help" href="http://bit.ly/280YsJd">?</a></div> <table border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="gutter"> <div class="line number1 index0 alt2">1</div> </td> <td class="code"> <div class="container"> <div class="line number1 index0 alt2"><code class="as3 plain">root@ubuntu1:~# curl -z</code> <code class="as3 value">3</code><code class="as3 plain">-Jan-</code><code class="as3 value">14</code> <code class="as3 plain">http:</code><code class="as3 comments">//example.com/myfile.gz</code></div> </div> </td> </tr> </tbody> </table> </div> </div> <p> </p> <p>The above command will download the file myfile.gz, if its modified after 3rd jan 2014. 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CURL command Tutorial in Linux with Example Usage

Transferring data from one place to another is one of the main task done using computers connected to a network. There are so many GUI tools out there to send and receive data, but when you are workin…

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