curl，简单认为是可以在命令行下访问url的一个工具。即增删改查。
curl是利用URL语法在命令行方式下工作的开源文件传输工具，使用curl可以简单实现常见的get/post请求。
查看curl的help文档
[hadoop@djt002 elasticsearch-2.4.3]$ curl -help
Usage: curl [options...] <url>
Options: (H) means HTTP/HTTPS only, (F) means FTP only
--anyauth Pick "any" authentication method (H)
-a/--append Append to target file when uploading (F/SFTP)
--basic Use HTTP Basic Authentication (H)
--cacert <file> CA certificate to verify peer against (SSL)
--capath <directory> CA directory to verify peer against (SSL)
-E/--cert <cert[:passwd]> Client certificate file and password (SSL)
--cert-type <type> Certificate file type (DER/PEM/ENG) (SSL)
--ciphers <list> SSL ciphers to use (SSL)
--compressed Request compressed response (using deflate or gzip)
-K/--config <file> Specify which config file to read
--connect-timeout <seconds> Maximum time allowed for connection
-C/--continue-at <offset> Resumed transfer offset
-b/--cookie <name=string/file> Cookie string or file to read cookies from (H)
-c/--cookie-jar <file> Write cookies to this file after operation (H)
--create-dirs Create necessary local directory hierarchy
--crlf Convert LF to CRLF in upload
--crlfile <file> Get a CRL list in PEM format from the given file
-d/--data <data> HTTP POST data (H)
--data-ascii <data> HTTP POST ASCII data (H)
--data-binary <data> HTTP POST binary data (H)
--data-urlencode <name=data/name@filename> HTTP POST data url encoded (H)
--delegation STRING GSS-API delegation permission
--digest Use HTTP Digest Authentication (H)
--disable-eprt Inhibit using EPRT or LPRT (F)
--disable-epsv Inhibit using EPSV (F)
-D/--dump-header <file> Write the headers to this file
--egd-file <file> EGD socket path for random data (SSL)
--engine <eng> Crypto engine to use (SSL). "--engine list" for list
-f/--fail Fail silently (no output at all) on HTTP errors (H)
-F/--form <name=content> Specify HTTP multipart POST data (H)
--form-string <name=string> Specify HTTP multipart POST data (H)
--ftp-account <data> Account data to send when requested by server (F)
--ftp-alternative-to-user <cmd> String to replace "USER [name]" (F)
--ftp-create-dirs Create the remote dirs if not present (F)
--ftp-method [multicwd/nocwd/singlecwd] Control CWD usage (F)
--ftp-pasv Use PASV/EPSV instead of PORT (F)
-P/--ftp-port <address> Use PORT with address instead of PASV (F)
--ftp-skip-pasv-ip Skip the IP address for PASV (F)
--ftp-ssl Try SSL/TLS for ftp transfer (F)
--ftp-ssl-ccc Send CCC after authenticating (F)
--ftp-ssl-ccc-mode [active/passive] Set CCC mode (F)
--ftp-ssl-control Require SSL/TLS for ftp login, clear for transfer (F)
--ftp-ssl-reqd Require SSL/TLS for ftp transfer (F)
-G/--get Send the -d data with a HTTP GET (H)
-g/--globoff Disable URL sequences and ranges using {} and []
-H/--header <line> Custom header to pass to server (H)
-I/--head Show document info only
-h/--help This help text
--hostpubmd5 <md5> Hex encoded MD5 string of the host public key. (SSH)
-0/--http1.0 Use HTTP 1.0 (H)
--ignore-content-length Ignore the HTTP Content-Length header
-i/--include Include protocol headers in the output (H/F)
-k/--insecure Allow connections to SSL sites without certs (H)
--interface <interface> Specify network interface/address to use
-4/--ipv4 Resolve name to IPv4 address
-6/--ipv6 Resolve name to IPv6 address
-j/--junk-session-cookies Ignore session cookies read from file (H)
--keepalive-time <seconds> Interval between keepalive probes
--key <key> Private key file name (SSL/SSH)
--key-type <type> Private key file type (DER/PEM/ENG) (SSL)
--krb <level> Enable Kerberos with specified security level (F)
--libcurl <file> Dump libcurl equivalent code of this command line
--limit-rate <rate> Limit transfer speed to this rate
-l/--list-only List only names of an FTP directory (F)
--local-port <num>[-num] Force use of these local port numbers
-L/--location Follow Location: hints (H)
--location-trusted Follow Location: and send auth to other hosts (H)
-M/--manual Display the full manual
--max-filesize <bytes> Maximum file size to download (H/F)
--max-redirs <num> Maximum number of redirects allowed (H)
-m/--max-time <seconds> Maximum time allowed for the transfer
--negotiate Use HTTP Negotiate Authentication (H)
-n/--netrc Must read .netrc for user name and password
--netrc-optional Use either .netrc or URL; overrides -n
-N/--no-buffer Disable buffering of the output stream
--no-keepalive Disable keepalive use on the connection
--no-sessionid Disable SSL session-ID reusing (SSL)
--noproxy Comma-separated list of hosts which do not use proxy
--ntlm Use HTTP NTLM authentication (H)
-o/--output <file> Write output to <file> instead of stdout
--pass <pass> Pass phrase for the private key (SSL/SSH)
--post301 Do not switch to GET after following a 301 redirect (H)
--post302 Do not switch to GET after following a 302 redirect (H)
-#/--progress-bar Display transfer progress as a progress bar
-x/--proxy <host[:port]> Use HTTP proxy on given port
--proxy-anyauth Pick "any" proxy authentication method (H)
--proxy-basic Use Basic authentication on the proxy (H)
--proxy-digest Use Digest authentication on the proxy (H)
--proxy-negotiate Use Negotiate authentication on the proxy (H)
--proxy-ntlm Use NTLM authentication on the proxy (H)
-U/--proxy-user <user[:password]> Set proxy user and password
--proxy1.0 <host[:port]> Use HTTP/1.0 proxy on given port
-p/--proxytunnel Operate through a HTTP proxy tunnel (using CONNECT)
--pubkey <key> Public key file name (SSH)
-Q/--quote <cmd> Send command(s) to server before file transfer (F/SFTP)
--random-file <file> File for reading random data from (SSL)
-r/--range <range> Retrieve only the bytes within a range
--raw Pass HTTP "raw", without any transfer decoding (H)
-e/--referer Referer URL (H)
-O/--remote-name Write output to a file named as the remote file
--remote-name-all Use the remote file name for all URLs
-R/--remote-time Set the remote file's time on the local output
-X/--request <command> Specify request command to use
--retry <num> Retry request <num> times if transient problems occur
--retry-delay <seconds> When retrying, wait this many seconds between each
--retry-max-time <seconds> Retry only within this period
-S/--show-error Show error. With -s, make curl show errors when they occur
-s/--silent Silent mode. Don't output anything
--socks4 <host[:port]> SOCKS4 proxy on given host + port
--socks4a <host[:port]> SOCKS4a proxy on given host + port
--socks5 <host[:port]> SOCKS5 proxy on given host + port
--socks5-hostname <host[:port]> SOCKS5 proxy, pass host name to proxy
--socks5-gssapi-service <name> SOCKS5 proxy service name for gssapi
--socks5-gssapi-nec Compatibility with NEC SOCKS5 server
-Y/--speed-limit Stop transfer if below speed-limit for 'speed-time' secs
-y/--speed-time Time needed to trig speed-limit abort. Defaults to 30
-2/--sslv2 Use SSLv2 (SSL)
-3/--sslv3 Use SSLv3 (SSL)
--stderr <file> Where to redirect stderr. - means stdout
--tcp-nodelay Use the TCP_NODELAY option
-t/--telnet-option <OPT=val> Set telnet option
-z/--time-cond <time> Transfer based on a time condition
-1/--tlsv1 Use TLSv1 (SSL)
--trace <file> Write a debug trace to the given file
--trace-ascii <file> Like --trace but without the hex output
--trace-time Add time stamps to trace/verbose output
-T/--upload-file <file> Transfer <file> to remote site
--url <URL> Set URL to work with
-B/--use-ascii Use ASCII/text transfer
-u/--user <user[:password]> Set server user and password
-A/--user-agent <string> User-Agent to send to server (H)
-v/--verbose Make the operation more talkative
-V/--version Show version number and quit
-w/--write-out <format> What to output after completion
-q If used as the first parameter disables .curlrc
[hadoop@djt002 elasticsearch-2.4.3]$
比如，
curl
-x 指定http请求的方法
GET POST PUT DELETE
-d 指定要传递的参数
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