cURL

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For the library organisation CURL, see Research Libraries UK. For other uses, see Curl (disambiguation).
Not to be confused with Curl (programming language).
cURL
Curl-logo.svg
CURL downloading CURL screenshot.png
Example output from curl -O
Original author(s)Daniel Stenberg[1]
Developer(s)Contributors to the cURL project
Initial release1996; 26 years ago (1996)[2]
Stable release
7.84.0[3] Edit this on Wikidata / 27 June 2022
Repository
Written inC
Operating system
PlatformCross-platform
TypeFTP client / HTTP client
Licensecurl[4][5]
Websitecurl.se Edit this at Wikidata

cURL (pronounced like "curl"[6], UK: /kəːl/, US: /kɝl/) is a computer software project providing a library (libcurl) and command-line tool (curl) for transferring data using various network protocols. The name stands for "Client URL".[7]

History[edit]

cURL was first released in 1996.[8] It was originally named httpget and then became urlget before adopting the current name of cURL.[9][10] The original author and lead developer is the Swedish developer Daniel Stenberg, who created cURL because he wanted to automate the fetching of currency exchange rates for IRC users.[2]

libcurl[edit]

libcurl is a free client-side URL transfer library,[11] supporting cookies, DICT, FTP, FTPS, Gopher, HTTP/1[12] (with HTTP/2 and HTTP/3 support), HTTP POST, HTTP PUT, HTTP proxy tunneling, HTTPS, IMAP, Kerberos, LDAP, MQTT, POP3, RTSP, RTMP, SCP, SMTP, and SMB. The library supports the file URI scheme, SFTP, Telnet, TFTP, file transfer resume, FTP uploading, HTTP form-based upload, HTTPS certificates, LDAPS, proxies, and user-plus-password authentication.[13]

The libcurl library is portable. It builds and works identically on many platforms, including AIX, AmigaOS, Android,[citation needed] BeOS, BlackBerry Tablet OS and BlackBerry 10,[14] OpenVMS, Darwin, DOS, FreeBSD, HP-UX, HURD, iOS, IRIX, Linux, macOS, NetBSD, NetWare, OpenBSD, OS/2, QNX Neutrino, RISC OS, Solaris, Symbian, Tru64, Ultrix, UnixWare, and Microsoft Windows.[15]

The libcurl library is free, thread-safe and IPv6 compatible. Bindings are available for more than 50 languages, including C/C++, Java, PHP and Python.[16]

The libcurl library supports GnuTLS, mbed TLS, NSS, gskit on IBM i, SChannel on Windows, Secure Transport on macOS and iOS, SSL/TLS through OpenSSL, Boringssl, libressl, AmiSSL, wolfSSL, BearSSL and rustls.[17]

cURL[edit]

cURL is a command-line tool for getting or sending data including files using URL syntax. Since cURL uses libcurl, it supports every protocol libcurl supports.[13]

cURL supports HTTPS and performs SSL certificate verification by default when a secure protocol is specified such as HTTPS. When cURL connects to a remote server via HTTPS, it will obtain the remote server certificate, then check against its CA certificate store the validity of the remote server to ensure the remote server is the one it claims to be. Some cURL packages are bundled with CA certificate store file. There are several options to specify a CA certificate such as --cacert and --capath. The --cacert option can be used to specify the location of the CA certificate store file. In the Windows platform, if a CA certificate file is not specified, cURL will look for a CA certificate file name “curl-ca-bundle.crt” in the following order:

  1. Directory where the cURL program is located.
  2. Current working directory.
  3. Windows system directory.
  4. Windows directory.
  5. Directories specified in the %PATH% environment variables.[18]

cURL will return an error message if the remote server is using a self-signed certificate, or if the remote server certificate is not signed by a CA listed in the CA cert file. -k or --insecure option can be used to skip certificate verification. Alternatively, if the remote server is trusted, the remote server CA certificate can be added to the CA certificate store file.

Examples[edit]

Basic use of cURL involves simply typing curl at the command line, followed by the URL of the output to retrieve: 

$ curl www.example.com

cURL defaults to displaying the output it retrieves to the standard output specified on the system (usually the terminal window). So running the command above would, on most systems, display the www.example.com source-code in the terminal window. The -o flag can be used to store the output in a file instead: 

$ curl -o example.html www.example.com

More options that change the tool's behavior are available.

See also[edit]

  • curl-loader – an open-source testing tool based on cURL
  • libwww – an early library that comes with a command line interface
  • PowerShell – the iwr (Invoke-WebRequest) Windows PowerShell had functionality akin to curl; class Web-client too.[19]
  • Web crawler – an internet bot that can crawl the web
  • Wget – similar command-line tool with no associated library but capable of recursive downloading.

References[edit]

  1. ^ Stenberg, Daniel (20 March 2015). "curl, 17 years old today". daniel.haxx.se. Retrieved 20 March 2015.
  2. ^ a b "History of curl - How curl Became Like This". curl. Archived from the original on September 30, 2017. Retrieved November 17, 2016. Daniel simply adopted an existing command-line open-source tool, httpget, that Brazilian Rafael Sagula had written and recently release version 0.1 of. After a few minor adjustments, it did just what he needed. […] HttpGet 1.0 was released on April 8th 1997 with brand new HTTP proxy support. […] Stenberg was spending time writing an IRC bot for an Amiga related channel on EFnet. He then came up with the idea to make currency-exchange calculations available to Internet Relay Chat (IRC) users.
  3. ^ Daniel Stenberg (27 June 2022). "curl 7.84.0". Retrieved 27 June 2022.
  4. ^ "curl License". spdx.org.
  5. ^ "curl - copyright". curl.se.
  6. ^ "curl - Frequently Asked Questions". curl.se.
  7. ^ Stenberg, Daniel. "Origin of the name". curl.se. Retrieved 2021-03-27.
  8. ^ "History of curl". fossies.org. Archived from the original on September 29, 2021.
  9. ^ "Changelog". 4 January 2020. Retrieved 4 January 2020. The first curl release. The tool was named urlget before this. And httpget before that.
  10. ^ Stenberg, Daniel (4 January 2020). "Restored complete curl changelog" (html). Haxx Se. Retrieved 2 January 2020.
  11. ^ Jones, M. Tim (8 September 2009). "Conversing through the Internet with cURL and libcurl - Using libcurl with C and Python". IBM Developerworks. Archived from the original on 14 April 2015. Retrieved 12 September 2018.
  12. ^ Stenberg, Daniel (5 August 2019). "http09: disable HTTP/0.9 by default in both tool and library". GitHub. Archived from the original (html) on 5 August 2019. Retrieved 5 August 2019. As the plan has been laid out in Deprecated. Update docs accordingly and verify in test 1174.
  13. ^ a b "curl - How To Use". curl.se.
  14. ^ "Open Source Components for the Native SDK for BlackBerry Tablet OS". Archived from the original on 2013-01-27. Retrieved 2017-09-19.
  15. ^ "Tar and Curl Come to Windows!". techcommunity.microsoft.com. March 22, 2019.
  16. ^ "libcurl bindings". curl.se.
  17. ^ "curl supports rustls | daniel.haxx.se". Retrieved 2022-01-01.
  18. ^ "curl - SSL CA Certificates". curl.se.
  19. ^ Del, Ryan (2 March 2018). "Comandi equivalenti a cURL e Wget per Windows command-line con Powershell" [cURL and Wget equivalent commands for Windows command-line with Powershell] (html). Ryadel (in Italian). Retrieved 4 January 2020. Per emulare il comportamento del comando Linux cURL, è sufficiente creare un file cURL.ps1 contenente la seguente riga di codice

External links[edit]

Wikibooks has a book on the topic of: Guide to Windows Commands
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