"cURL" - Client for URL

Linux Tutorials - Herong's Tutorial Examples

∟"cURL" - Client for URL

This section provides a tutorial example on how to use 'cURL' command to send requests to a remote server in different protocols in URL format.

What Is "cURL"? - "cURL" is a client tool for Internet protocols represented in URL format.

Main features of "cURL":

Supports multiple Internet protocols, including DICT, FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET and TFTP.
Supports multiple file download with URL patterns.
Supports request data to be sent to the server.

Here are some examples of installing and using "wget" command.

1. Install "wget" on a CentOS computer.

herong$ sudo dnf install curl

...
Installed:
  curl-7.61.1-22.el8.x86_64

2. Download the home page on the local Web server. Received data is displayed to the console.

herong$ curl http://localhost

<html>
<body>
<p>Hello world!</p>
</body>
</html>

3. Download the home page on the local Web server, including both header and body parts.

herong$ curl --include http://localhost

HTTP/1.1 200 OK
Server: Apache/2.4.37 (centos) OpenSSL/1.1.1g
ETag: "73-5cbe9c0a43a66"
Accept-Ranges: bytes
Content-Length: 115
Content-Type: text/html; charset=UTF-8

<html>
...
</html>

4. Send a POST request with data to a Web site.

herong$ curl --data 'login=emma&password=123' --request POST \
  https://google.com/login

...

5. Display debugging information on an HTTPS request.

herong$ curl --verbose https://www.oracle.com/index.html
* Connected to www.oracle.com (23.63.32.30) port 443 (#0)
* ALPN, offering http/1.1
* successfully set certificate verify locations:
*   CAfile: /usr/local/ssl/cacert.pem
  CApath: none
} [5 bytes data]
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
} [512 bytes data]
* TLSv1.3 (IN), TLS handshake, Server hello (2):
{ [122 bytes data]
* TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
{ [35 bytes data]
* TLSv1.3 (IN), TLS handshake, Certificate (11):
{ [4369 bytes data]
* TLSv1.3 (IN), TLS handshake, CERT verify (15):
{ [79 bytes data]
* TLSv1.3 (IN), TLS handshake, Finished (20):
{ [52 bytes data]
* TLSv1.3 (OUT), TLS change cipher, Change cipher spec (1):
} [1 bytes data]
* TLSv1.3 (OUT), TLS handshake, Finished (20):
} [52 bytes data]
* SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384
* ALPN, server accepted to use http/1.1
* Server certificate:
*  subject: C=US; ST=California; L=Redwood City; O=Oracle Corporation; ...
*  start date: May 24 00:00:00 2022 GMT
*  expire date: Sep 17 23:59:59 2022 GMT
*  subjectAltName: host "www.oracle.com" matched cert's "www.oracle.com"
*  issuer: C=US; O=DigiCert Inc; CN=DigiCert TLS Hybrid ECC ...
*  SSL certificate verify ok.
} [5 bytes data]
> GET /index.html HTTP/1.1
> Host: www.oracle.com
> User-Agent: curl/7.71.1
> Accept: */*

...