举例：ip route help如下：
Usage: ip route { list | flush } SELECTOR
ip route save SELECTOR
ip route restore
ip route showdump
ip route get [ ROUTE_GET_FLAGS ] ADDRESS
[ from ADDRESS iif STRING ]
[ oif STRING ] [ tos TOS ]
[ mark NUMBER ] [ vrf NAME ]
[ uid NUMBER ]
ip route { add | del | change | append | replace } ROUTE
SELECTOR := [ root PREFIX ] [ match PREFIX ] [ exact PREFIX ]
[ table TABLE_ID ] [ vrf NAME ] [ proto RTPROTO ]
[ type TYPE ] [ scope SCOPE ]
ROUTE := NODE_SPEC [ INFO_SPEC ]
NODE_SPEC := [ TYPE ] PREFIX [ tos TOS ]
[ table TABLE_ID ] [ proto RTPROTO ]
[ scope SCOPE ] [ metric METRIC ]
[ ttl-propagate { enabled | disabled } ]
INFO_SPEC := NH OPTIONS FLAGS [ nexthop NH ]...
NH := [ encap ENCAPTYPE ENCAPHDR ] [ via [ FAMILY ] ADDRESS ]
[ dev STRING ] [ weight NUMBER ] NHFLAGS
FAMILY := [ inet | inet6 | ipx | dnet | mpls | bridge | link ]
OPTIONS := FLAGS [ mtu NUMBER ] [ advmss NUMBER ] [ as [ to ] ADDRESS ]
[ rtt TIME ] [ rttvar TIME ] [ reordering NUMBER ]
[ window NUMBER ] [ cwnd NUMBER ] [ initcwnd NUMBER ]
[ ssthresh NUMBER ] [ realms REALM ] [ src ADDRESS ]
[ rto_min TIME ] [ hoplimit NUMBER ] [ initrwnd NUMBER ]
[ features FEATURES ] [ quickack BOOL ] [ congctl NAME ]
[ pref PREF ] [ expires TIME ] [ fastopen_no_cookie BOOL ]
TYPE := { unicast | local | broadcast | multicast | throw |
unreachable | prohibit | blackhole | nat }
TABLE_ID := [ local | main | default | all | NUMBER ]
SCOPE := [ host | link | global | NUMBER ]
NHFLAGS := [ onlink | pervasive ]
RTPROTO := [ kernel | boot | static | NUMBER ]
PREF := [ low | medium | high ]
TIME := NUMBER[s|ms]
BOOL := [1|0]
FEATURES := ecn
ENCAPTYPE := [ mpls | ip | ip6 | seg6 | seg6local ]
ENCAPHDR := [ MPLSLABEL | SEG6HDR ]
SEG6HDR := [ mode SEGMODE ] segs ADDR1,ADDRi,ADDRn [hmac HMACKEYID] [cleanup]
SEGMODE := [ encap | inline ]
ROUTE_GET_FLAGS := [ fibmatch ]
<> 表示 一定要有这个参数
[] 表示可选
{a|b|c} {}好像和 | 符号联合使用 表示一定要从a、b或c之间挑选1个
这里面还有粗体和细体字 、斜体字和正常字体 的区别 ，限于cnblogs格式以上的help格式无法正常显示出来
黑色粗体字 是 原样不动 斜体非加粗字 是需要变为实际的参数值