Linux帮助命令

帮助命令：man

man 命令

获取命令的帮助

如下：

[root@localhost ~]# man ls

LS(1)    User Commands    LS(1)

NAME
       ls - list directory contents

SYNOPSIS
       ls [OPTION]... [FILE]...

DESCRIPTION
       ...

其中LS(1)中的1表示级别。

man的级别

• 1：查看命令的帮助
• 2：查看可被内核调用的函数的帮助
• 3：查看函数和函数库的帮助
• 4：查看特殊文件的帮助（主要是/dev目录下的文件）
• 5：查看配置文件的帮助
• 6：查看游戏的帮助
• 7：查看其它杂项的帮助
• 8：查看系统管理员可用命令的帮助
• 9：查看和内核相关文件的帮助

查看命令拥有的级别

man -f 命令
whatis 命令

[root@localhost ~]# man -f ls
ls (1)               - list directory contents
ls (1p)              - list directory contents
[root@localhost ~]# man -f passwd
sslpasswd (1ssl)     - compute password hashes
passwd (1)           - update user's authentication tokens
passwd (5)           - password file
[root@localhost ~]# whatis passwd
sslpasswd (1ssl)     - compute password hashes
passwd (1)           - update user's authentication tokens
passwd (5)           - password file
[root@localhost ~]# 

查看和命令有关的所有帮助

man -k 命令
apropos 命令

[root@localhost ~]# man -k passwd
chpasswd (8)         - 批量更新密码
gpasswd (1)          - 管理员 /etc/group 和 /etc/gshadow
fgetpwent_r (3)      - get passwd file entry reentrantly
getpwent_r (3)       - get passwd file entry reentrantly
grub2-mkpasswd-pbkdf2 (1) - Generate a PBKDF2 password hash.
kpasswd (1)          - change a user's Kerberos password
lpasswd (1)          - Change group or user password
lppasswd (1)         - add, change, or delete digest passwords.
pam_localuser (8)    - require users to be listed in /etc/passwd
passwd (1)           - update user's authentication tokens
sslpasswd (1ssl)     - compute password hashes
passwd (5)           - password file
passwd2des (3)       - RFS password encryption
pwhistory_helper (8) - Helper binary that transfers password hashes from passwd or shadow to opasswd
saslpasswd2 (8)      - set a user's sasl password
smbpasswd (5)        - The Samba encrypted password file
smbpasswd (8)        - change a user's SMB password

[root@localhost ~]# apropos passwd
chpasswd (8)         - 批量更新密码
gpasswd (1)          - 管理员 /etc/group 和 /etc/gshadow
fgetpwent_r (3)      - get passwd file entry reentrantly
getpwent_r (3)       - get passwd file entry reentrantly
grub2-mkpasswd-pbkdf2 (1) - Generate a PBKDF2 password hash.
kpasswd (1)          - change a user's Kerberos password
lpasswd (1)          - Change group or user password
lppasswd (1)         - add, change, or delete digest passwords.
pam_localuser (8)    - require users to be listed in /etc/passwd
passwd (1)           - update user's authentication tokens
sslpasswd (1ssl)     - compute password hashes
passwd (5)           - password file
passwd2des (3)       - RFS password encryption
pwhistory_helper (8) - Helper binary that transfers password hashes from passwd or shadow to opasswd
saslpasswd2 (8)      - set a user's sasl password
smbpasswd (5)        - The Samba encrypted password file
smbpasswd (8)        - change a user's SMB password

选项帮助：--help

命令 --help

获取命令选项的帮助

[root@localhost ~]# ls --help

shell内部命令的帮助：help

help 命令

[root@localhost ~]# help ls
-bash: help: 没有与 `ls' 匹配的帮助主题。尝试 `help help' 或者 `man -k ls' 或者 `info ls'。
[root@localhost ~]# help cd
cd: cd [-L|[-P [-e]]] [dir]
    Change the shell working directory.
    
    Change the current directory to DIR.  The default DIR is the value of the
    HOME shell variable.
    
    ...
    
    Options:
        -L  force symbolic links to be followed
        -P  use the physical directory structure without following symbolic
      links
        -e  if the -P option is supplied, and the current working directory
      cannot be determined successfully, exit with a non-zero status
    
    The default is to follow symbolic links, as if `-L' were specified.
    
    Exit Status:
    Returns 0 if the directory is changed, and if $PWD is set successfully when
    -P is used; non-zero otherwise.
[root@localhost ~]# 

因为 ls 不是shell内部命令，所以无法用help，cd是shell内部命令，可以查看该命令的帮助。

可以用 whereis 确定是否是shell内部命令，如果不是，那么它会在/bin目录下，否者将不存在命令的路径。

查看详细命令帮助：info

info 命令

-回车：进入子帮助页面（带有*号标记）
-u：进入上层页面
-n：进入下一个帮助小节
-p：进入上一个帮助小节
-q：退出