1.9.1.man
English: manual
Get help with a command or configuration file
View help information for the ls command
man ls
Command usage similar to the combination of more and less
Space: turn page
q : quit
Enter: scroll down line by line
Enter / and search content, press Enter to search
When viewing the configuration file help, you cannot use an absolute path, just enter the configuration file name directly.
View the help information of the configuration file yum.conf
man yum.conf
View help for passwd configuration file
[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 shows that passwd is a command and a configuration file with the same name. At this time, using man passwd shows the help of the command, not the help of the configuration file.
passwd.1.gz stands for command help, 1 means command help, 5 means configuration file help , for example: passwd.5.gz
What if I want to view the configuration file help at this point? The following command
man 5 passwd
1.9.2.whatis
whatis View a brief description of a command and what it does.
[root@localhost ~]# whatis ls
ls (1) - list directory contents
1.9.3.apropos
View a brief description of the configuration file, what does it do
[root@localhost ~]# apropos yum.conf
yum.conf (5) - Configuration file for yum(8).
1.9.4.–help
command --help
Almost all commands have this option
[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
It is also help information, similar to man, but in a different way.
1.9.6.help
How can I tell if it's a built-in command?
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)
View help information for the umask built-in command
[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.