Linux help instructions

man command:

Get help information

man [要查询的指令]

The effect after executing man ls:

help command:

Display the help information inside the shell

[要查询的指令] --help

help [要查询的指令]
但是这种有的不行耶(例如help ls就不行),不知道怎么回事

The effect after executing ls --help:

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