许多初学者安装完一个Linux操作系统后不知从哪里入手学习Linux，特别是感觉到没有帮助信息。Linux发行版本对用户通过的技术支持时间比较短。其实当你安装了一个完整的Linux系统后，其中已经包含了一个强大的帮助，只是可能你还没有发现和使用它们的技巧。下面以RHEL 5.0为例，帮助你深入挖掘隐藏在Linux系统中的帮助信息。
B.1 命令行下帮助信息
Linux发展到今天，很多功能已经可以在可视化的界面中来完成。不过在很多情况下，命令还是非常有用的，它可以提高效率，并且可以加深对Linux系统的了解。Linux默认的Shell是Bourne Again Shell，它是Bourne Shell的扩展，简称bash，与Bourne Shell完全向后兼容，并且在Bourne Shell的基础上增加了很多特性。bash是标准的命令行"shell"，也就是在Linux里等同于DOS的命令行处理器"COMMAND.COM"。bash放在/bin/bash中，可以提供如命令补全、命令编辑和命令历史表A－等功能。它有灵活和强大的编程接口，同时又有很友好的用户界面。
B.1.1 help
bash的内部命令有40个，主要包括exit、less、lp、kill、cd、pwd、fc、fg等。bash内置的命令列表A－可以通过在命令行敲入help即可获得。这些内部命令没有独立的命令程序（即你无法搜索到这些命令）和帮助文件，help命令提供这些命令的在线帮助，有趣的是help命令本身也是内部命令。下面使用help命令获取它提供帮助命令的列表：
＃help
GNU bash, version 3.00.15(1)-release (i386-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.
%[DIGITS | WORD] [&] (( expression ))
. filename [arguments] :
[ arg... ] [[ expression ]]
alias [-p] [name[=value] ... ] bg [job_spec]
bind [-lpvsPVS] [-m keymap] [-f fi break [n]
builtin [shell-builtin [arg ...]] caller [EXPR]
case WORD in [PATTERN [| PATTERN]. cd [-L|-P] [dir]
command [-pVv] command [arg ...] compgen [-abcdefgjksuv] [-o option
complete [-abcdefgjksuv] [-pr] [-o continue [n]
declare [-afFirtx] [-p] [name[=val dirs [-clpv] [+N] [-N]
disown [-h] [-ar] [jobspec ...] echo [-neE] [arg ...]
enable [-pnds] [-a] [-f filename] eval [arg ...]
exec [-cl] [-a name] file [redirec exit [n]
export [-nf] [name[=value] ...] or false
fc [-e ename] [-nlr] [first] [last fg [job_spec]
for NAME [in WORDS ... ;] do COMMA for (( exp1; exp2; exp3 )); do COM
function NAME { COMMANDS ; } or NA getopts optstring name [arg]
hash [-lr] [-p pathname] [-dt] [na help [-s] [pattern ...]
history [-c] [-d offset] [n] or hi if COMMANDS; then COMMANDS; [ elif
jobs [-lnprs] [jobspec ...] or job kill [-s sigspec | -n signum | -si
let arg [arg ...] local name[=value] ...
logout popd [+N | -N] [-n]
printf format [arguments] pushd [dir | +N | -N] [-n]
pwd [-PL] read [-ers] [-u fd] [-t timeout] [
readonly [-af] [name[=value] ...] return [n]
select NAME [in WORDS ... ;] do CO set [--abefhkmnptuvxBCHP] [-o opti
shift [n] shopt [-pqsu] [-o long-option] opt
source filename [arguments] suspend [-f]
test [expr] time [-p] PIPELINE
times trap [-lp] [arg signal_spec ...]
true type [-afptP] name [name ...]
typeset [-afFirtx] [-p] name[=valu ulimit [-SHacdflmnpstuv] [limit]
umask [-p] [-S] [mode] unalias [-a] name [name ...]
unset [-f] [-v] [name ...] until COMMANDS; do COMMANDS; done
variables - Some variable names an wait [n]
while COMMANDS; do COMMANDS; done { COMMANDS ; }
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上面以help命令把自己作为参数来获得自己的帮助。使用help命令提供某命令的帮助方法非常简单，在help命令后空格输入命令名称即可。
help命令提供的kill命令参数很详细，如果你对Linux有一定了解，往往只需要主要的语法，那么可以使用"－s"参数：
＃help －s kill
kill: kill [-s sigspec | -n signum |
-sigspec] [pid | job]... or kill -l [sigspec] |
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