man bash:

  Special Parameters
       The shell treats several parameters specially.   These  parameters  may
       only be referenced; assignment to them is not allowed.
       *      Expands  to  the positional parameters, starting from one.  When
              the expansion occurs within double quotes, it expands to a  sin‐
              gle word with the value of each parameter separated by the first
              character of the IFS special variable.  That is, "$*" is equiva‐
              lent to "$1c$2c...", where c is the first character of the value
              of the IFS variable.  If IFS is unset, the parameters are  sepa‐
              rated  by  spaces.   If  IFS  is null, the parameters are joined
              without intervening separators.
       @      Expands to the positional parameters, starting from  one.   When
              the  expansion  occurs  within  double  quotes,  each  parameter
              expands to a separate word.  That is, "$@" is equivalent to "$1"
              "$2"  ...   If the double-quoted expansion occurs within a word,
              the expansion of the first parameter is joined with  the  begin‐
              ning  part  of  the original word, and the expansion of the last
              parameter is joined with the last part  of  the  original  word.
              When  there  are no positional parameters, "$@" and $@ expand to
              nothing (i.e., they are removed).
       #      Expands to the number of positional parameters in decimal.
       ?      Expands to the exit status of the most recently  executed  fore‐
              ground pipeline.
       -      Expands  to  the  current option flags as specified upon invoca‐
              tion, by the set builtin command, or  those  set  by  the  shell
              itself (such as the -i option).
       $      Expands  to  the  process ID of the shell.  In a () subshell, it
              expands to the process ID of the current  shell,  not  the  sub‐
              shell.
       !      Expands  to  the  process ID of the most recently executed back‐
              ground (asynchronous) command.
       0      Expands to the name of the shell or shell script.  This  is  set
              at shell initialization.  If bash is invoked with a file of com‐
              mands, $0 is set to the name of that file.  If bash  is  started
              with  the  -c option, then $0 is set to the first argument after
              the string to be executed, if one is present.  Otherwise, it  is
              set  to  the file name used to invoke bash, as given by argument
              zero.
       _      At shell startup, set to the absolute pathname  used  to  invoke
              the  shell or shell script being executed as passed in the envi‐
              ronment or argument list.  Subsequently,  expands  to  the  last
              argument  to the previous command, after expansion.  Also set to
              the full pathname used  to  invoke  each  command  executed  and
              placed in the environment exported to that command.  When check‐
              ing mail, this parameter holds the name of the  mail  file  cur‐
              rently being checked.

http://blog.sina.com.cn/s/blog_6739945f0100sosu.html

特殊的shell变量:

$0  获取当前执行的shell脚本的文件名

$n  获取当前执行的shell脚本的第n个参数值，n=1..9

$*  获取当前shell的所有参数 “$1 $2 $3 …，受IFS控制

$#  获取当前shell命令行中参数的总个数

$$  获取当前shell的进程号（PID）

$!  执行上一个指令的PID

$?  获取执行的上一个指令的返回值(0 为成功， 非零为失败)

$@  这个程序的所有参数 “$1″ “$2″ “$3″ “…”，不受IFS控制

注：

IFS:IFS(Internal Field Seperator)在Linux的shell中预设的分隔符，用来把command line分解成word（字段）。IFS可以是White Space（空白键）、Tab（ 表格键）、Enter（ 回车键）中的一个或几个。

对于$@与$*的区别如下：
    这两个参数的不同点主要在于它们扩展参数的方式不同。当使用$*时，只是简单地在不保留引用的情况下扩展每个参数，这样会存在问题：当参数中存在空格时，该参数将被识别为多个参数使用，如：mytar-t "my tarfile.tar"，使用$*时将被识别成my、tar、file.tar坧个文件，而使用$@时则识别成一个文件。