都说Emacs是万能的，但从没想到emacs居然可以作为脚本语言来编写linux系统shell script。对于熟悉linux shell编程的同学来说。这也许是开始eLisp世界的一个更好的入口。。。
下面的例子示范了shell script中最常用的几个任务：
1. 读取命令行参数
2. 遍历命令行参数
3. 输出到stdout
4. 输出到stderr
5. 执行外部命令
6. 获取外部命令输出
hello.el
#!/usr/local/bin/emacs --script
;; find your emacs with : "which emacs" and set to the first line
(princ "This is message to stdout\n")
(message "This is err message to stderr")
(setq args command-line-args)
(princ (format "\nread command line with variable : %s\n" args))
(princ "\nenum arguments with car\n")
(setq i 0)
(while (setq arg (car args))
(princ (format "arg[%d] = %s\n" i arg))
(setq args (cdr args))
(setq i (1+ i)))
(princ "\nenum arguments with nth\n")
(setq args command-line-args)
(setq i 0)
(while (setq arg (nth i args))
(princ (format "arg[%d] = %s\n" i arg))
(setq i (1+ i)))
(princ "\nrun shell command with shell-command-to-string\n")
(setq ret (shell-command-to-string "date"))
(princ (format "shell execute result = %s" ret))
(princ "\nstart speed test\n")
(setq num 0)
(setq total 0)
(setq start (current-time))
(while (<= num 10000000)
(setq total (+ total num))
(setq num (+ num 1))
)
(setq end (current-time))
(princ (shell-command-to-string "date"))
(setq cost (- (nth 1 end) (nth 1 start)))
(princ (format "loop for %d times cost %d s\n" num cost))
(princ (format "speed = %d loops/s\n" (/ num cost)))
运行结果：
xxx@ubuntu:~/src/emacs$ ./hello.el 1 2 3 "4 5 6 7 8"
This is message to stdout
This is err message to stderr
read command line with variable : (/usr/local/bin/emacs -scriptload ./hello.el 1 2 3 4 5 6 7 8)
enum arguments with car
arg[0] = /usr/local/bin/emacs
arg[1] = -scriptload
arg[2] = ./hello.el
arg[3] = 1
arg[4] = 2
arg[5] = 3
arg[6] = 4 5 6 7 8
enum arguments with nth
arg[0] = /usr/local/bin/emacs
arg[1] = -scriptload
arg[2] = ./hello.el
arg[3] = 1
arg[4] = 2
arg[5] = 3
arg[6] = 4 5 6 7 8
run shell command with shell-command-to-string
shell execute result = Mon Aug 17 21:09:36 HKT 2015
start speed test
Mon Aug 17 21:09:38 HKT 2015
loop for 10000001 times cost 2 s
speed = 5000000 loops/s
