腳本預設參數

1. Shell 腳本執行時參數的預設變數為 $0, $1, $2,...，對應如下：

   /path/to/scriptname  opt1  opt2  opt3  opt4  ...
          $0             $1    $2    $3    $4   ...
   

2. sh04.sh 列出執行命令名稱、前三個參數：

   [dywang@dywmac zzz]$ cat sh04.sh
   #!/bin/bash
   echo "The script name is ==> $0"
   [ -n "$1" ] && echo "The 1st paramter is ==> $1" || exit 0
   [ -n "$2" ] && echo "The 2nd paramter is ==> $2" || exit 0
   [ -n "$3" ] && echo "The 3th paramter is ==> $3" || exit 0
   

3. 執行 sh04.sh 加三個參數，列出執行命令名稱及三個參數：

   [dywang@dywmac zzz]$ sh sh04.sh abc 123 cde
   The script name is ==> sh04.sh
   The 1st paramter is ==> abc
   The 2nd paramter is ==> 123
   The 3th paramter is ==> cde
   

4. 執行 sh04.sh 加兩個參數，列出執行命令名稱及兩個參數後退出腳本。

   [dywang@dywmac zzz]$ sh sh04.sh abc 123
   The script name is ==> sh04.sh
   The 1st paramter is ==> abc
   The 2nd paramter is ==> 123