curl是一个非常实用的、用来与服务器之间传输数据的工具；支持的协议包括 (DICT, FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP)，curl设计为无用户交互下完成工作；curl提供了一大堆非常有用的功能，包括代理访问、用户认证、ftp上传下载、HTTP POST、SSL连接、cookie支持、断点续传。

curl  is  a  tool  to transfer data from or to a server, using one of the sup-
       ported protocols (DICT, FILE, FTP, FTPS, GOPHER,  HTTP,  HTTPS,  IMAP,  IMAPS,
       LDAP,  LDAPS, POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TEL-
       NET and TFTP). The command is designed to work without user interaction.
curl offers a busload of useful tricks like proxy  support,  user  authentica-
       tion,  FTP  upload, HTTP post, SSL connections, cookies, file transfer resume,
       Metalink, and more. As you will see below, the number of  features  will  make
       your head spin!

       curl  is  powered by libcurl for all transfer-related features. See libcurl(3)
       for details.