如何查看系统内置的shell命令及帮助信息

1.打开终端，输入help命令可以查看系统默认的shell(通常是bash)的内置的shell命令列表：

[tansheng@localhost ~]$ help
GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)
These shell commands are defined internally.  Type `help' to see this list.
Type `help name' to find out more about the function `name'.
Use `info bash' to find out more about the shell in general.
Use `man -k' or `info' to find out more about commands not in this list.

A star (*) next to a name means that the command is disabled.

job_spec [&]                            history [-c] [-d offset]
or hist>
(( expression ))                        if COMMANDS; then COMMANDS; [ elif C>
. filename [arguments]                  jobs [-lnprs] [jobspec ...] or jobs >
:                                       kill [-s sigspec | -n signum | -sigs>
[ arg... ]                              let arg [arg ...]
[[ expression ]]                        local [option] name[=value] ...
alias [-p] [name[=value] ... ]          logout

bg [job_spec ...]                       mapfile [-n count] [-O origin] [-s c>
bind [-lpvsPVS] [-m keymap] [-f filen>  popd [-n] [+N | -N]
break
printf [-v var] format [arguments]
builtin [shell-builtin [arg ...]]       pushd [-n] [+N | -N | dir]
caller [expr]                           pwd [-LP]
case WORD in [PATTERN [| PATTERN]...)>  read [-ers] [-a array] [-d delim] [->
cd [-L|-P] [dir]                        readarray [-n count] [-O origin] [-s>
command [-pVv] command [arg ...]        readonly [-af] [name[=value] ...] or>

2.我们如果对某一个shell命令感兴趣，也可以用help command 来查看具体的命令详情：

[tansheng@localhost ~]$ help fg
fg: fg [job_spec]
Move job to the foreground.

Place the job identified by JOB_SPEC in the foreground, making it the
current job.  If JOB_SPEC is not present, the shell's notion of the
current job is used.

Exit Status:
Status of command placed in foreground, or failure if an error occurs.
[tansheng@localhost ~]$

3.我们想了解alias命令的用法，可以使用 help alias查看：

[tansheng@localhost ~]$ help alias
alias: alias [-p] [name[=value] ... ]
Define or display aliases.

Without arguments, `alias' prints the list of aliases in the reusable
form `alias NAME=VALUE' on standard output.

Otherwise, an alias is defined for each NAME whose VALUE is given.
A trailing space in VALUE causes the next word to be checked for
alias substitution when the alias is expanded.

Options:
-p    Print all defined aliases in a reusable format

Exit Status:
alias returns true unless a NAME is supplied for which no alias has been
defined.
[tansheng@localhost ~]$