[root@iZ2ze2m3z176dpbiaolifiZ ~]# cat --help
Usage: cat [OPTION]... [FILE]...
Concatenate FILE(s), or standard input, to standard output.
-A, --show-all           equivalent to -vET

-b, --number-nonblank    number nonempty output lines, overrides -n

-e                       equivalent to -vE

-E, --show-ends          display $ at end of each line

-n, --number             number all output lines

-s, --squeeze-blank      suppress repeated empty output lines

-t                       equivalent to -vT

-T, --show-tabs          display TAB characters as ^I

-u                       (ignored)

-v, --show-nonprinting   use ^ and M- notation, except for LFD and TAB

--help     display this help and exit

--version  output version information and exit
With no FILE, or when FILE is -, read standard input.
Examples:

cat f - g  Output f's contents, then standard input, then g's contents.

cat        Copy standard input to standard output.
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>

For complete documentation, run: info coreutils 'cat invocation'

[root@iZ2ze2m3z176dpbiaolifiZ ~]# more --help

more: unknown option -help

Usage: more [options] file...
Options:

-d        display help instead of ring bell

-f        count logical, rather than screen lines

-l        suppress pause after form feed

-p        do not scroll, clean screen and display text

-c        do not scroll, display text and clean line ends

-u        suppress underlining

-s        squeeze multiple blank lines into one

-NUM      specify the number of lines per screenful

+NUM      display file beginning from line number NUM

+/STRING  display file beginning from search string match

-V        output version information and exit

[root@iZ2ze2m3z176dpbiaolifiZ ~]# 

BASH_BUILTINS(1)                                                                                                        General Commands Manual                                                                                                        BASH_BUILTINS(1)
NAME

bash,  :, ., [, alias, bg, bind, break, builtin, caller, cd, command, compgen, complete, compopt, continue, 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, unalias, unset, wait - bash built-in commands, see bash(1)
BASH BUILTIN COMMANDS

Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options.  The :, true, false, and test builtins do not accept options and do not treat -- specially.  The  exit,

logout,  break,  continue,  let, and shift builtins accept and process arguments beginning with - without requiring --.  Other builtins that accept arguments but are not specified as accepting options interpret arguments beginning with - as invalid options

and require -- to prevent this interpretation.

: [arguments]

No effect; the command does nothing beyond expanding arguments and performing any specified redirections.  A zero exit code is returned.

[root@iZ2ze2m3z176dpbiaolifiZ ~]# help cd
cd: cd [-L|[-P [-e]]] [dir]
    Change the shell working directory.
Change the current directory to DIR.  The default DIR </span><span style="color: #0000ff;">is</span><span style="color: #000000;"> the value of the
HOME shell variable.

The variable CDPATH defines the search path </span><span style="color: #0000ff;">for</span><span style="color: #000000;"> the directory containing
DIR.  Alternative directory names </span><span style="color: #0000ff;">in</span><span style="color: #000000;"> CDPATH are separated by a colon (:).
A null directory name </span><span style="color: #0000ff;">is</span><span style="color: #000000;"> the same as the current directory.  If DIR begins
with a slash (</span>/), then CDPATH <span style="color: #0000ff;">is</span> <span style="color: #0000ff;">not</span><span style="color: #000000;"> used.

If the directory </span><span style="color: #0000ff;">is</span> <span style="color: #0000ff;">not</span> found, <span style="color: #0000ff;">and</span> the shell option `cdable_vars<span style="color: #800000;">'</span><span style="color: #800000;"> is set,</span>
the word <span style="color: #0000ff;">is</span><span style="color: #000000;"> assumed to be  a variable name.  If that variable has a value,
its value </span><span style="color: #0000ff;">is</span> used <span style="color: #0000ff;">for</span><span style="color: #000000;"> DIR.

Options:
    </span>-<span style="color: #000000;">L    force symbolic links to be followed
    </span>-<span style="color: #000000;">P    use the physical directory structure without following symbolic
    links
    </span>-e    <span style="color: #0000ff;">if</span> the -P option <span style="color: #0000ff;">is</span> supplied, <span style="color: #0000ff;">and</span><span style="color: #000000;"> the current working directory
    cannot be determined successfully, exit with a non</span>-<span style="color: #000000;">zero status

The default </span><span style="color: #0000ff;">is</span> to follow symbolic links, as <span style="color: #0000ff;">if</span> `-L<span style="color: #800000;">'</span><span style="color: #800000;"> were specified.</span>

    
    Exit Status:
    Returns 0 if the directory is changed, and if $PWD is set successfully when
    -P is used; non-zero otherwise.
[root@iZ2ze2m3z176dpbiaolifiZ ~]# help history
history: history [-c] [-d offset] [n] or history -anrw [filename] or history -ps arg [arg...]
    Display or manipulate the history list.
Display the history list with line numbers, prefixing each modified
entry with a `</span>*<span style="color: #800000;">'</span><span style="color: #800000;">.  An argument of N lists only the last N entries.</span>

    
    Options:
      -c    clear the history list by deleting all of the entries
      -d offset    delete the history entry at offset OFFSET.
  </span>-a    append history lines <span style="color: #0000ff;">from</span><span style="color: #000000;"> this session to the history file
  </span>-n    read all history lines <span style="color: #0000ff;">not</span> already read <span style="color: #0000ff;">from</span><span style="color: #000000;"> the history file
  </span>-r    read the history file <span style="color: #0000ff;">and</span><span style="color: #000000;"> append the contents to the history
    list
  </span>-<span style="color: #000000;">w    write the current history to the history file
    </span><span style="color: #0000ff;">and</span><span style="color: #000000;"> append them to the history list

  </span>-p    perform history expansion on each ARG <span style="color: #0000ff;">and</span><span style="color: #000000;"> display the result
    without storing it </span><span style="color: #0000ff;">in</span><span style="color: #000000;"> the history list
  </span>-<span style="color: #000000;">s    append the ARGs to the history list as a single entry

If FILENAME </span><span style="color: #0000ff;">is</span> given, it <span style="color: #0000ff;">is</span><span style="color: #000000;"> used as the history file.  Otherwise,
</span><span style="color: #0000ff;">if</span> $HISTFILE has a value, that <span style="color: #0000ff;">is</span> used, <span style="color: #0000ff;">else</span> ~/<span style="color: #000000;">.bash_history.

If the $HISTTIMEFORMAT variable </span><span style="color: #0000ff;">is</span> set <span style="color: #0000ff;">and</span> <span style="color: #0000ff;">not</span> null, its value <span style="color: #0000ff;">is</span><span style="color: #000000;"> used
as a format string </span><span style="color: #0000ff;">for</span> strftime(3) to <span style="color: #0000ff;">print</span><span style="color: #000000;"> the time stamp associated
with each displayed history entry.  No time stamps are printed otherwise.

Exit Status:
Returns success unless an invalid option </span><span style="color: #0000ff;">is</span> given <span style="color: #0000ff;">or</span><span style="color: #000000;"> an error occurs.

[root@iZ2ze2m3z176dpbiaolifiZ ~]# 

SHUTDOWN(8)                                                                                                                     shutdown                                                                                                                    SHUTDOWN(8)
NAME

shutdown - Halt, power-off or reboot the machine
SYNOPSIS

shutdown [OPTIONS...] [TIME] [WALL...]
DESCRIPTION

shutdown may be used to halt, power-off or reboot the machine.
   The first argument may be a time string (which </span><span style="color: #0000ff;">is</span> usually <span style="color: #800000;">"</span><span style="color: #800000;">now</span><span style="color: #800000;">"</span>). Optionally, this may be followed by a wall message to be sent to all logged-<span style="color: #0000ff;">in</span><span style="color: #000000;"> users before going down.

   The time string may either be </span><span style="color: #0000ff;">in</span> the format <span style="color: #800000;">"</span><span style="color: #800000;">hh:mm</span><span style="color: #800000;">"</span> <span style="color: #0000ff;">for</span> hour/minutes specifying the time to execute the shutdown at, specified <span style="color: #0000ff;">in</span> 24h clock format. Alternatively it may be <span style="color: #0000ff;">in</span> the syntax <span style="color: #800000;">"</span><span style="color: #800000;">+m</span><span style="color: #800000;">"</span> referring to the specified number of minutes m <span style="color: #0000ff;">from</span> now.  <span style="color: #800000;">"</span><span style="color: #800000;">now</span><span style="color: #800000;">"</span>
   <span style="color: #0000ff;">is</span> an alias <span style="color: #0000ff;">for</span> <span style="color: #800000;">"</span><span style="color: #800000;">+0</span><span style="color: #800000;">"</span>, i.e. <span style="color: #0000ff;">for</span> triggering an immediate shutdown. If no time argument <span style="color: #0000ff;">is</span> specified, <span style="color: #800000;">"</span><span style="color: #800000;">+1</span><span style="color: #800000;">"</span> <span style="color: #0000ff;">is</span><span style="color: #000000;"> implied.

   Note that to specify a wall message you must specify a time argument, too.

   If the time argument </span><span style="color: #0000ff;">is</span> used, 5 minutes before the system goes down the /run/nologin file <span style="color: #0000ff;">is</span> created to ensure that further logins shall <span style="color: #0000ff;">not</span><span style="color: #000000;"> be allowed.

OPTIONS

The following options are understood:
   </span>--<span style="color: #000000;">help
       Print a short help text </span><span style="color: #0000ff;">and</span><span style="color: #000000;"> exit.

   </span>-H, --<span style="color: #000000;">halt
       Halt the machine.

   </span>-P, --<span style="color: #000000;">poweroff
       Power</span>-<span style="color: #000000;">off the machine (the default).

   </span>-r, --<span style="color: #000000;">reboot
       Reboot the machine.

   </span>-<span style="color: #000000;">h
       Equivalent to </span>--poweroff, unless --halt <span style="color: #0000ff;">is</span><span style="color: #000000;"> specified.

   </span>-<span style="color: #000000;">k
       Do </span><span style="color: #0000ff;">not</span> halt, power-<span style="color: #000000;">off, reboot, just write wall message.

   </span>--no-<span style="color: #000000;">wall
       Do </span><span style="color: #0000ff;">not</span> send wall message before halt, power-<span style="color: #000000;">off, reboot.

   </span>-<span style="color: #000000;">c
       Cancel a pending shutdown. This may be used cancel the effect of an invocation of shutdown with a time argument that </span><span style="color: #0000ff;">is</span> <span style="color: #0000ff;">not</span> <span style="color: #800000;">"</span><span style="color: #800000;">+0</span><span style="color: #800000;">"</span> <span style="color: #0000ff;">or</span> <span style="color: #800000;">"</span><span style="color: #800000;">now</span><span style="color: #800000;">"</span><span style="color: #000000;">.

EXIT STATUS

On success, 0 is returned, a non-zero failure code otherwise.
SEE ALSO

systemd(1), systemctl(1), halt(8), wall(1)
Manual page shutdown(8) line 1 (press h for help or q to quit)

[root@iZ2ze2m3z176dpbiaolifiZ ~]# ls /sbin/poweroff 
/sbin/poweroff
[root@iZ2ze2m3z176dpbiaolifiZ ~]# ls /sbin/halt 
/sbin/halt
[root@iZ2ze2m3z176dpbiaolifiZ ~]# ls /sbin/reboot 
/sbin/reboot
[root@iZ2ze2m3z176dpbiaolifiZ ~]# ls -l /sbin/poweroff 
lrwxrwxrwx 1 root root 16 Oct 15  2017 /sbin/poweroff -> ../bin/systemctl
[root@iZ2ze2m3z176dpbiaolifiZ ~]# ls -l /sbin/halt 
lrwxrwxrwx 1 root root 16 Oct 15  2017 /sbin/halt -> ../bin/systemctl
[root@iZ2ze2m3z176dpbiaolifiZ ~]# ls -l /sbin/reboot 
lrwxrwxrwx 1 root root 16 Oct 15  2017 /sbin/reboot -> ../bin/systemctl
[root@iZ2ze2m3z176dpbiaolifiZ ~]#