解开获取 aria2c 帮助信息的误区

本来想获取 aria2c 的 proxy 相关帮助信息

aria2c -h|grep proxy

运行结果什么都不显示，明明是有这个设置功能，为什么不显示呢？经查询，原来是这样才可以

aria2c -h#http|grep proxy

                              connection to HTTP/FTP/proxy server. After the
 --http-proxy=PROXY           Use a proxy server for HTTP. To override a
                              previously defined proxy, use "".
                              See also the --all-proxy option.
 --https-proxy=PROXY          Use a proxy server for HTTPS. To override a
                              previously defined proxy, use "".
                              See also the --all-proxy option.
 --all-proxy=PROXY            Use a proxy server for all protocols. To override
                              a previously defined proxy, use "".
                              proxy server for a particular protocol using the
                              --http-proxy, --https-proxy and --ftp-proxy
 --no-proxy=DOMAINS           Specify comma separated hostnames, domains or
                              proxy should not be used.
 --proxy-method=METHOD        Set the method to use in proxy request.
 --http-proxy-user=USER       Set user for --http-proxy.
 --http-proxy-passwd=PASSWD   Set password for --http-proxy.
 --https-proxy-user=USER      Set user for --https-proxy.
 --https-proxy-passwd=PASSWD  Set password for --https-proxy.
 --all-proxy-user=USER        Set user for --all-proxy.
 --all-proxy-passwd=PASSWD    Set password for --all-proxy.

继续研究发现，想获取所有的帮助信息怎么办呢？

aria2c -h#help

Usage: aria2c [OPTIONS] [URI | MAGNET | TORRENT_FILE | METALINK_FILE]...
Printing options tagged with '#help'.
See 'aria2c -h#help' to know all available tags.
Options:
 -h, --help[=TAG|KEYWORD]     Print usage and exit.
                              The help messages are classified with tags. A tag
                              starts with "#". For example, type "--help=#http"
                              to get the usage for the options tagged with
                              "#http". If non-tag word is given, print the usage
                              for the options whose name includes that word.

                              Possible Values: #basic, #advanced, #http, #https, #ftp, #metalink, #bittorrent, #cookie,
#hook, #file, #rpc, #checksum, #experimental, #deprecated, #help, #all
                              Default: #basic
                              Tags: #basic, #help

Refer to man page for more information.

原来是这样的，哈哈！