Linux curl Command Explained with Examples
Introduction
Transferring data to and from a server requires tools that support the necessary network protocols. Linux has multiple tools created for this purpose, the most popular being curl and wget.
This tutorial will show you how to use the curl command and provide you with an exhaustive list of the available options.
What Is the curl Command?
curl (short for “Client URL”) is a command line tool that enables data transfer over various network protocols. It communicates with a web or application server by specifying a relevant URL and the data that need to be sent or received.
curl is powered by libcurl, a portable client-side URL transfer library. You can use it directly on the command line or include it in a script. The most common use cases for curl are:
1、Downloading files from the internet
2、Endpoint testing
3、Debugging
4、Error logging
curl Syntax
The basic curl syntax is as follows:
1 | curl [options/URLs] |
For example:
1 | curl https://www.gnu.org/gnu/gnu.html |
If you specify a URL that leads to a file, you can use curl to download the file to your local system:
1 | curl [url] > [local-file] |
The syntax of URLs that are part of the command depends on the protocol. Multiple URLs that differ in one part are written together using braces:
1 | http://example.{first,second,third}.com |
Alphanumeric series are written with brackets:
1 | ftp://ftp.url.com/file[1-100].txt |
While nested sequences are not supported, multiple sequences are allowed:
1 | http://url.com/archive[2010-2020]/vol[1-4]/part{a,b,c}.html |
curl Protocols
curl supports numerous protocols for data transfer. Find the complete list below.
| Protocol | Description |
|---|---|
| DICT | A dictionary network protocol for querying dictionary servers about the meanings of words. |
| FILE | A URL scheme for obtaining a file from the local file system using curl. |
| FTP, FTPS | File Transfer Protocol, used for file transfers between clients and servers. FTPS is the version of the same protocol with an added SSL/TLS security layer. |
| GOPHER, GOPHERS | An old protocol for searching, retrieving, and distributing internet documents, a precursor of HTTP. GOPHERS is the version of the same protocol with an added SSL/TLS security layer. |
| HTTP, HTTPS | Hypertext Transfer Protocol, used for web and internet data transfer. HTTPS is the version of the same protocol with an added SSL/TLS security layer. |
| IMAP, IMAPS | Internet Message Access Protocol, used for email access and management. IMAPS is the version of the same protocol with an added SSL/TLS security layer. |
| LDAP, LDAPS | Lightweight Directory Access Protocol, used for distributed directory information access and management. LDAPS is the version of the same protocol with an added SSL/TLS security layer. |
| MQTT | Message Queuing Telemetry Transport - a protocol for data exchange between small devices, usually IoT systems. |
| POP3, POP3S | Post Office Protocol version 3 - a protocol for email retrieval from a server. POP3S is the version of the same protocol with an added SSL/TLS security layer. |
| RTMP | Real-Time Messaging Protocol - a streaming protocol for audio, video, and other data. |
| RTSP | Real Time Streaming Protocol, used for streaming media servers management. |
| SCP | Secure Copy - a protocol for copying files to and from an SSH server. |
| SFTP | SSH File Transfer Protocol - a version of the File Transfer Protocol using the SSH connection. |
| SMB, SMBS | Server Message Block - a protocol for managing shared access to files and computer peripherals. SMBS is the version of the same protocol with an added SSL/TLS security layer. |
| SMTP, SMPTS | Simple Mail Transfer Protocol - an email protocol for easy transmission of email. SMTPS is the version of the same protocol with an added SSL/TLS security layer. |
| TELNET | An application layer protocol for bidirectional interactive text-oriented communication. |
| TFTP | Trivial File Transfer Protocol, used for uploading or downloading files to or from a remote host. |
curl Command Options
curl accepts a wide array of options, which makes it an extremely versatile command. Options start with one or two dashes. If they do not require additional values, the single-dash options can be written together. For example, the command that utilizes the -O, -L, and -v options can be written as:
1 | curl -OLv [url] |
The list of all the available options is given below.
| Option | Description |
|---|---|
| –abstract-unix-socket |
Connect through abstract Unix socket instead through a network. Example: curl –abstract-unix-socket socketpath https://example.com |
| –alt-svc |
Enable alt-svc parser Example: curl –alt-svc svc.txt https://example.com |
man curl or curl –manual
use man curl or curl –manual for see many command and options