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Title : Curl Command: Definition and Usage
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Curl Command: Definition and Usage
[ad_1]Curl command is a type of command that is commonly used on Unix-based systems. Actually, the term is an abbreviation of "Client URL".
The usefulness of this command includes checking connectivity to URLs and transferring data. Additionally, this type of command can be used in a variety of protocols, including:
- HTTP and HTTPS
- FTP and FTPS
- IMAP and IMAPS
- POP3 and POP3S
- SMB and SMBS
- SFTP
- SCP
- TELNET
- GOPHER
- LDAP and LDAPS
- SMTP and SMTPS
In addition to extensive protocol support, the Curl command also comes with libcurl, a library URL transfer that works on the client side.
Now, let's learn how to use the Curl command.
How to Check the Curl Version
To get started, log in to your VPS hosting account through SSH. Then check the version of Curl that you are using with the following command:
curl --version
The output that you will get shows the version of Curl and what protocols are supported.
Basic Curl Syntax Command
In this section, you will learn about using the Curl command. Following is the basic syntax used in Curl:
curl [OPTIONS] [URL]
The most basic purpose of Curl is to display the contents of a page. For example, the command below will show the main page of the website mysiteku.com:
curl websiteku.com
Curl works specifically. If you don't specify the protocol used for the above command, Curl will consider it as HTTP.
Curl Command to Download File
You can use this command to download files remotely. However, keep in mind that there are two commands that give different results:
- Command -O will retain the name of the file that was downloaded and save it in the current directory
- Command -o lets you specify the name of the downloaded file and the storage directory
Consider the following example in order to understand the above explanation:
curl -O http://websiteku.com/testfile.tar.gz
With this command, the file downloaded will be named testfile.tar.gz. Now check the following command:
curl -o newtestfile.tar.gz http://websiteku.com/testfile.tar.gz
As a result, the name of the file downloaded will change to newtestfile.tar.gz.
The curl command can also be used to continue the downloading process that was interrupted. The following commands are required:
curl -C - -o http://websiteku.com/testfile.tar.gz
In addition, this command also functions to download several files at once, as in the example below:
curl -o http://websiteku.com/testfile.tar.gz -o http://domainku.com/myfile.tar.gz
If you want to download more than one file from multiple URLs, you must specify all of them in one file. Curl commands can be combined by xargs to do the task.
For example, suppose you have written all the URLs that you want to download in the allurls.txt file. The command below will download all files from the URL mentioned:
xargs -n 1 curl -o < allurls.txt
Curl Command for HTTP
Curl can be used on a proxy server. If you are on a proxy server and use port 8090 on sampleproxy.com, you can download the files using the command below:
curl -x sampleproxy.com:8090 -U username:password -O http://websiteku.com/testfile .tar.gz
You can override -U username: password in the above case if the proxy does not require the authentication method.
In general, HTTP requests have a header. The header sends information about the remote web server that you are accessing along with the actual request. With this command, you can check information from the header. Here's how:
curl -I www.websiteku.com
In addition, this command also allows you to make GET and POST requests. Following is an example of a GET request:
curl http://mydomain.com
Whereas the example commands for making POST requests are like this:
curl -data “text=Hello” https://mydomain.com/firstpage.jsp
text = Hello is the POST request parameter, which is similar to the HTML form.
In addition, you can specify various HTTP methods at the same time in one Curl command. You do this by using -next as in the following example:
curl -data “text=Hello” https://mydomain.com/firstpage.jsp --next https://mydomain.com/displayresult.jsp
The above command contains a POST request and is followed by a GET request.
Each HTTP request has a user agent that shows the user's internet browser information. On the other hand, the Curl request contains the Curl and the version number indicated by the user agent. To make a Curl request, enter the following command:
“GET / HTTP/1.1” 200 “_” “curl/7/29/0”
However, you can replace the information in the user agent with this command:
curl -I http://mydomain.com --user-agent “My new Browser”
Now the output from the previous command will be:
“GET / HTTP/1.1” 200 “_” “My new Browser”
Also Read: 50+ Basic Linux Commands You Must Know
Curl Command for Cookies
The curl command can also be used to check what cookies are downloaded at a URL. If you access https://www.websiteku.com, you can save the cookies and access them with paint or VM editor.
The following are examples of commands that are used for these needs:
curl --cookie-jar Mycookies.txt https://www.contohsitus.com /index.html -O
If you save several cookies in a file, you can also send them to a website. The command is as follows:
curl --cookie Mycookies.txt https://www.contohsitus.com
Curl Command for FTP
As mentioned at the beginning of the article, the Curl command can be used on an FTP connection to manage files remotely. Below is a sample command to download the file:
curl -u username:password -O ftp://sampleftpserver/testfile.tar.gz
In that command, ftp: // sampleftpserver is an FTP server that accepts connections. If you want an anonymous connection, you don't need to enter a username: password.
In addition, you can use the Curl command to upload files with an FTP connection. Here is the command:
curl -u username:password -T testfile.tar.gz ftp://sampleftpserver
Limiting Output Curl
There is no way to find out how much bandwidth is consumed by the Curl output. Therefore, you can limit its use. The command below will limit your bandwidth to 100K:
curl --limit-rate 100K http://websiteku.com/samplefile.tar.gz -O
Closing
Curl is a type of command that is widely used because of its usefulness. Especially if you often use SSH to access the server. In addition, Curl supports various protocols.
This article only discusses basic Curl commands. If you want to learn more about various other commands, open the guide available with this command:
man curl
Hopefully this article is useful for you. If you have questions about the topics that have been discussed, do not hesitate to leave comments in the column provided.
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