Programming in Shell -- I

最新推荐文章于 2024-11-21 13:56:10 发布

Graveworm

最新推荐文章于 2024-11-21 13:56:10 发布

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分类专栏： Linux 文章标签： shell file

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本文介绍了Shell脚本的基础知识，包括数值运算、条件判断、文件属性测试等实用技巧，并通过具体示例展示了如何使用if语句进行逻辑控制。

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1. 数值运算

var=$((expression))
   total=$(($firstnu*secnu))
   echo $total;
2. test 命令可用于判断某文件是否存在或其属性(如是否是文件或目录)
   fredchen@fredchen:~$ test -e dd || echo "this file does not exsist"
   this file does not exsist
   fredchen@fredchen:/dev$ test -b ttyze
   fredchen@fredchen:/dev$ test -b ttyze || echo "not a block dev"
   not a block dev
   fredchen@fredchen:/dev$ test -b sda && echo "it is a block dev"
   it is a block dev

   test ! x file //! 用于条件求反，当file不具x属性时，返回true
3. [] 同样可以用于条件判断
   read -p "please make your choice: " choice

   [ "$choice" == "y" ] && echo "you accept it!" && exit 0
   [ "$choice" == "n" ] && echo "you reject it!" && exit 0
   echo "we can not determine your choice!" && exit 0

4. shell script的默认变量 $0 $1 $2 $3 ...

$0 = script name
   $1 = para1
   $2 = para2

5. if判断
   if [ expression1 ] || [ expression2 ]; then   //semicolon and then
      statement1   //no semiconlon
      statement2   //no semiconlon
   fi

   if [ expression1 ] && [ expression2 ]; then //semicolon and then
      statement1   //no semiconlon
      statement2   //no semiconlon
   else [ expression1 ] || [ expression2 ]; then //semicolon and then
      statement3   //no semiconlon
      statement4   //no semiconlon
   fi

   if [ expression1 ] && [ expression2 ]; then //semicolon and then
      statement1   //no semiconlon
      statement2   //no semiconlon
   elif [ expression1 ] || [ expression2 ]; then //semicolon and then
      statement3   //no semiconlon
      statement4   //no semiconlon
   else
      statement3   //no semiconlon
      statement4   //no semiconlon
   fi