1.9.1.man
英文：manual
获得命令或者配置文件的帮助信息
查看ls命令的帮助信息
man ls
类似于more和less合在一起的命令使用方式
空格：翻页
q：退出
回车：一行一行向下翻
输入/ 和搜索内容，按回车可以搜索
查看配置文件帮助时，不能使用绝对路径，直接输入配置文件名称就可以了。
查看配置文件yum.conf的帮助信息
man yum.conf
查看passwd配置文件的帮助
[root@localhost ~]# which passwd
/usr/bin/passwd
[root@localhost ~]# whereis passwd
passwd: /usr/bin/passwd /etc/passwd /usr/share/man/man1/passwd.1.gz
whereis 显示了passwd是一个命令，同时还一个同名的配置文件，此时使用man passwd显示的是命令的帮助，而不是配置文件的帮助。
passwd.1.gz代表的是命令的帮助，1表示命令帮助，5表示配置文件的帮助，例如：passwd.5.gz
此时要查看配置文件帮助怎么办？如下命令
man 5 passwd
1.9.2.whatis
whatis 查看一个命令的简述，是干什么的。
[root@localhost ~]# whatis ls
ls (1) - list directory contents
1.9.3.apropos
查看配置文件的简述，是做什么的
[root@localhost ~]# apropos yum.conf
yum.conf (5) - Configuration file for yum(8).
1.9.4.–help
命令 –help
所有的命令几乎都有这个选项
[root@localhost ~]# whatis --help
Usage: whatis [OPTION...] KEYWORD...
-d, --debug emit debugging messages
-v, --verbose print verbose warning messages
-r, --regex interpret each keyword as a regex
-w, --wildcard the keyword(s) contain wildcards
-l, --long do not trim output to terminal width
-C, --config-file=FILE use this user configuration file
-L, --locale=LOCALE define the locale for this search
-m, --systems=SYSTEM use manual pages from other systems
-M, --manpath=PATH set search path for manual pages to PATH
-s, --sections=LIST, --section=LIST
search only these sections (colon-separated)
-?, --help give this help list
--usage give a short usage message
-V, --version print program version
Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.
Report bugs to [email protected].
[root@localhost ~]#
1.9.5.info
也是帮助信息，和man差不多，只是方式不一样。
1.9.6.help
怎么判断是不是内置命令？
man cd
BASH_BUILTINS(1) General Commands Manual BASH_BUILTINS(1)
NAME
bash, :, ., [, alias, bg, bind, break, builtin, caller, cd, command, compgen, complete, compopt, con‐
tinue, declare, dirs, disown, echo, enable, eval, exec, exit, export, false, fc, fg, getopts, hash,
help, history, jobs, kill, let, local, logout, mapfile, popd, printf, pushd, pwd, read, readonly,
return, set, shift, shopt, source, suspend, test, times, trap, true, type, typeset, ulimit, umask, una‐
lias, unset, wait - bash built-in commands, see bash(1)
查看umask内置命令的帮助信息
[root@localhost ~]# help umask
umask: umask [-p] [-S] [mode]
Display or set file mode mask.
Sets the user file-creation mask to MODE. If MODE is omitted, prints
the current value of the mask.
If MODE begins with a digit, it is interpreted as an octal number;
otherwise it is a symbolic mode string like that accepted by chmod(1).
Options:
-p if MODE is omitted, output in a form that may be reused as input
-S makes the output symbolic; otherwise an octal number is output
Exit Status:
Returns success unless MODE is invalid or an invalid option is given.