shell流程控制

　　流程控制是面向过程的编程思想，是对问题的解决步骤的代码化！

号外：mysql的内连接删除
delete a from table_aaa  as a  inner join table_bb as b set a.djxh=b.djxh;


  跳脱字符，接触特殊字符的含义，原样输出字符 escape 
||  //or if/while
$#  //参数总数量，局部
$*  //完全的参数字符串，整体  $1..$x,不含$0
$@  

#!/bin/bash  //不写默认sh
echo "are you ok? $*"    //依次输出参数

shift n  //向左移动n个字符，默认n是1，左移1
test expression //测试表达式，true/false

//shell流程控制
#if
fi exp1 ; then
    commands
fi

if exp1  //对称行if -->fi
then
    commands
elif exp2
    commands
else exp3
    commands
fi

#case
case var1 in
str1)
    commands;;     //;;终止符跳出判断
str2)
    commands;;
*)
    commands;;
esac

#for
for var1 in list   //对list的每个参数，走一遍操作  
do
    commands
done

for var1    //对着参数操作
do
    commands
done

#while until
while : | true |exp  //条件为真则继续操作
do    
    commands
done

until exp  //条件为假不在继续操作，
do
    commands
done

#break/continue

break //退出当前循环结构
continue //终止继续，执行下一次循环