Linux curl examples.
Introduction
In this post you will learn about curl command in Linux and then have a look at some common curl examples.
What is curl?
Curl is a command-line utility used for sending and getting data using URLs. curl supports various protocols, including HTTP, HTTPS, FTP, SCP, SFTP, TFTP, LDAP, TELNET, POP3, SMTP and others. It is often used by web developers for crafting various HTTP requests. I will use Ubuntu 18.04 for demo purposes, but you can use any Linux distribution.
How to install curl in Ubuntu?
Before we go through some curl examples we need to install it. The following command installs curl in Ubuntu:
$ sudo apt install curl
Example 1. curl version
You can run the following command to find the exact version of curl and which protocols it supports:
$ curl --version curl 7.58.0 (x86_64-pc-linux-gnu) libcurl/7.58.0 OpenSSL/1.1.0g zlib/1.2.11 libidn2/2.0.4 libpsl/0.19.1 (+libidn2/2.0.4) nghttp2/1.30.0 librtmp/2.3 Release-Date: 2018-01-24 Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtmp rtsp smb smbs smtp smtps telnet tftp Features: AsynchDNS IDN IPv6 Largefile GSS-API Kerberos SPNEGO NTLM NTLM_WB SSL libz TLS-SRP HTTP2 UnixSockets HTTPS-proxy PSL
Example 2. GET request
You can download a file from the http server and print its contents to STDOUT, using a simple GET request:
$ curl http://example.com
You can save the output instead of printing it, by redirecting the output to a file, like that:
$ curl http://example.com > example_com.txt % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 1270 100 1270 0 0 3836 0 --:--:-- --:--:-- --:--:-- 3836
Another way to download a file is to specify a full path to it and use -O option:
$ curl -O http://example.com/index.html % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 1270 100 1270 0 0 3825 0 --:--:-- --:--:-- --:--:-- 3825
Example 3. View HTTP response headers
You can use -I option to view headers of HTTP response:
$ curl -I example.com HTTP/1.1 200 OK Content-Encoding: gzip Accept-Ranges: bytes Cache-Control: max-age=604800 Content-Type: text/html; charset=UTF-8 Date: Wed, 14 Nov 2018 12:59:14 GMT Etag: "1541025663+gzip" Expires: Wed, 21 Nov 2018 12:59:14 GMT Last-Modified: Fri, 09 Aug 2013 23:54:35 GMT Server: ECS (dca/2498) X-Cache: HIT Content-Length: 606
Example 4. POST request
It is also possible to issue POST request with specified parameter “name=Orkhan”, as shown below:
$ curl --data "name=Orkhan" http://example.com
Example 5. Follow redirect link
You can use -L option to follow redirects. For example, if you try to retrieve Google’s homepage without -L option you will only get this:
$ curl http://google.com <HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8"> <TITLE>301 Moved</TITLE></HEAD><BODY> <H1>301 Moved</H1> The document has moved <A HREF="http://www.google.com/">here</A>. </BODY></HTML>
Now, if you specify -L option you will get the desired destination page:
$ curl -L http://google.com
Example 6. Download a file from FTP server
The following command shows the contents of a remote FTP directory:
$ curl -u administrator ftp://192.168.37.79 Enter host password for user 'administrator': drwxr-xr-x 2 1000 1000 4096 May 22 2018 Desktop drwxr-xr-x 2 1000 1000 4096 May 22 2018 Documents drwxr-xr-x 3 1000 1000 4096 Nov 15 13:59 Downloads drwxr-xr-x 2 1000 1000 4096 May 22 2018 Music drwxr-xr-x 2 1000 1000 4096 May 22 2018 Pictures drwxr-xr-x 2 1000 1000 4096 May 22 2018 Public drwxr-xr-x 2 1000 1000 4096 May 22 2018 Templates drwxr-xr-x 2 1000 1000 4096 May 22 2018 Videos -rw-r--r-- 1 1000 1000 8980 May 22 2018 examples.desktop -rw-r--r-- 1 1000 1000 30 Nov 25 16:28 test.txt
You can download a file from the FTP server using the following command:
$ curl -u administrator -O ftp://192.168.37.79/test.txt
Enter host password for user 'administrator':
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 30 100 30 0 0 258 0 --:--:-- --:--:-- --:--:-- 258
-u – used to specify the username for our FTP connection
-O – downloads the specified file to the current working directory
Example 7. Upload a file to FTP server
You can also upload a file to a FTP server, using the options -u and -T:
$ curl -u administrator -T ./backup.txt ftp://192.168.37.79
Enter host password for user 'administrator':
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 12 0 0 100 12 0 70 --:--:-- --:--:-- --:--:-- 70
-u – specifies username which should be used to connect to FTP server
-T – specifies that we want to transfer/upload the file to FTP server
Conclusion.
This post gave you an overview of using curl command in Linux.
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