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curl – A file transfer tool that works on the command line using URL rules

Curl is a command-line tool that is used to transfer data to and from a server using various protocols such as HTTP, HTTPS, FTP, FTPS, SCP, SFTP, TFTP, Telnet, DICT, LDAP, LDAPS, IMAP, SMTP, POP3, RTSP, and others. It is a versatile tool that can be used to download or upload files, test APIs, and perform other network-related tasks.

Overview

The basic syntax of curl is as follows:

curl [options] [URL]

This command will fetch the contents of the URL and display them on the terminal. If no options are specified, curl will use the GET method to retrieve the data. Here are some examples of how to use curl:

# Download a file
curl -O https://example.com/file.zip

# Upload a file
curl -F 'file=@/path/to/local/file' https://example.com/upload.php

# Send a POST request with JSON data
curl -X POST -H 'Content-Type: application/json' -d '{"key": "value"}' https://example.com/api

# Download a file with authentication
curl -u username:password https://example.com/file.zip

In the first example, the -O option is used to save the downloaded file with the same name as the remote file. The second example shows how to upload a file using the -F option. The third example demonstrates how to send a POST request with JSON data using the -X, -H, and -d options. Finally, the last example shows how to download a file that requires authentication using the -u option.

Options

Here is a table of some of the most commonly used options for curl:

Option Description
-X <method> Sets the HTTP method to use (GET, POST, PUT, DELETE, etc.)
-H <header> Adds a custom header to the request
-d <data> Sends data in the request body
-F <name=@file> Uploads a file
-o <file> Saves output to a file
-O Saves output to a file with the same name as the remote file
-u <user:password> Sets the username and password for authentication
-L Follows redirects
-s Silent mode (suppresses progress meter and error messages)

There are many other options available for curl, which can be found in the manual page (man curl) or by running curl --help.

Troubleshooting tips

If you encounter issues while using curl, here are some common troubleshooting tips:

  • Check the URL to make sure it is correct and accessible.
  • Check your network connection to make sure you are connected to the internet.
  • Check your firewall settings to make sure curl is not being blocked.
  • Use the -v option to enable verbose output and see more details about the request and response.
  • If you are uploading a file, make sure the file exists and is readable.
  • If you are downloading a file, make sure you have write permission in the directory where you are saving the file.

Notes

  • Curl can be used in scripts to automate tasks that involve transferring data over the network.
  • Curl is often used to test APIs and web services.
  • Curl is not installed by default on some Linux distributions, so you may need to install it manually.

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