Docs Overview

Features -- what curl can do

curl tool

• config file support
• multiple URLs in a single command line
• range "globbing" support: [0-13], {one,two,three}
• multiple file upload on a single command line
• redirect stderr
• parallel transfers

libcurl

• URL RFC 3986 syntax
• custom maximum download time
• custom lowest download speed acceptable
• custom output result after completion
• guesses protocol from hostname unless specified
• supports .netrc
• progress bar with time statistics while downloading
• standard proxy environment variables support
• have run on 101 operating systems and 28 CPU architectures
• selectable network interface for outgoing traffic
• IPv6 support on Unix and Windows
• happy eyeballs dual-stack IPv4 + IPv6 connects
• persistent connections
• SOCKS 4 + 5 support, with or without local name resolving
• pre-proxy support, for proxy chaining
• supports username and password in proxy environment variables
• operations through HTTP proxy "tunnel" (using CONNECT)
• replaceable memory functions (malloc, free, realloc, etc)
• asynchronous name resolving
• both a push and a pull style interface
• international domain names (IDN)
• transfer rate limiting
• stable API and ABI
• TCP keep alive
• TCP Fast Open
• DNS cache (that can be shared between transfers)
• non-blocking single-threaded parallel transfers
• Unix domain sockets to server or proxy
• DNS-over-HTTPS
• uses non-blocking name resolves
• selectable name resolver backend

URL API

• parses RFC 3986 URLs
• generates URLs from individual components
• manages "redirects"

Header API

• easy access to HTTP response headers, from all contexts
• named headers
• iterate over headers

TLS

• selectable TLS backend(s)
• TLS False Start
• TLS version control
• TLS session resumption
• key pinning
• mutual authentication
• Use dedicated CA cert bundle
• Use OS-provided CA store
• separate TLS options for HTTPS proxy

HTTP

• HTTP/0.9 responses are optionally accepted
• HTTP/1.0
• HTTP/1.1
• HTTP/2, including multiplexing and server push
• GET
• PUT
• HEAD
• POST
• multipart formpost (RFC 1867-style)
• authentication: Basic, Digest, NTLM (9) and Negotiate (SPNEGO) to server and proxy
• resume transfers
• follow redirects
• maximum amount of redirects to follow
• custom HTTP request
• cookie get/send fully parsed
• reads/writes the Netscape cookie file format
• custom headers (replace/remove internally generated headers)
• custom user-agent string
• custom referrer string
• range
• proxy authentication
• time conditions
• via HTTP proxy, HTTPS proxy or SOCKS proxy
• HTTP/2 or HTTP/1.1 to HTTPS proxy
• retrieve file modification date
• Content-Encoding support for deflate, gzip, brotli and zstd
• "Transfer-Encoding: chunked" support in uploads
• HSTS
• alt-svc
• ETags
• HTTP/1.1 trailers, both sending and getting

HTTPS

• HTTP/3
• using client certificates
• verify server certificate
• via HTTP proxy, HTTPS proxy or SOCKS proxy
• select desired encryption
• select usage of a specific TLS version
• ECH

FTP

• download
• authentication
• Kerberos 5
• active/passive using PORT, EPRT, PASV or EPSV
• single file size information (compare to HTTP HEAD)
• 'type=' URL support
• directory listing
• directory listing names-only
• upload
• upload append
• upload via http-proxy as HTTP PUT
• download resume
• upload resume
• custom ftp commands (before and/or after the transfer)
• simple "range" support
• via HTTP proxy, HTTPS proxy or SOCKS proxy
• all operations can be tunneled through proxy
• customizable to retrieve file modification date
• no directory depth limit

FTPS

• implicit ftps:// support that use SSL on both connections
• explicit "AUTH TLS" and "AUTH SSL" usage to "upgrade" plain ftp:// connection to use SSL for both or one of the connections

SSH (both SCP and SFTP)

• selectable SSH backend
• known hosts support
• public key fingerprinting
• both password and public key auth

SFTP

• both password and public key auth
• with custom commands sent before/after the transfer
• directory listing

TFTP

• download
• upload

TELNET

• connection negotiation
• custom telnet options
• stdin/stdout I/O

LDAP

• full LDAP URL support

DICT

• extended DICT URL support

FILE

• URL support
• upload
• resume

SMB

• SMBv1 over TCP and SSL
• download
• upload
• authentication with NTLMv1

SMTP

• authentication: Plain, Login, CRAM-MD5, Digest-MD5, NTLM, Kerberos 5 and External
• send emails
• mail from support
• mail size support
• mail auth support for trusted server-to-server relaying
• multiple recipients
• via http-proxy

SMTPS

• implicit smtps:// support
• explicit "STARTTLS" usage to "upgrade" plain smtp:// connections to use SSL
• via http-proxy

POP3

• authentication: Clear Text, APOP and SASL
• SASL based authentication: Plain, Login, CRAM-MD5, Digest-MD5, NTLM, Kerberos 5 and External
• list emails
• retrieve emails
• enhanced command support for: CAPA, DELE, TOP, STAT, UIDL and NOOP via custom requests
• via http-proxy

POP3S

• implicit pop3s:// support
• explicit STLS usage to "upgrade" plain pop3:// connections to use SSL
• via http-proxy

IMAP

• authentication: Clear Text and SASL
• SASL based authentication: Plain, Login, CRAM-MD5, Digest-MD5, NTLM, Kerberos 5 and External
• list the folders of a mailbox
• select a mailbox with support for verifying the UIDVALIDITY
• fetch emails with support for specifying the UID and SECTION
• upload emails via the append command
• enhanced command support for: EXAMINE, CREATE, DELETE, RENAME, STATUS, STORE, COPY and UID via custom requests
• via http-proxy

IMAPS

• implicit imaps:// support
• explicit "STARTTLS" usage to "upgrade" plain imap:// connections to use SSL
• via http-proxy

MQTT

• Subscribe to and publish topics using URL scheme mqtt://broker/topic