参数置换变量

Posted 2020-08-21 胖头猫

格式	var1为空	var1不为空
var2=${var1:-string}	var2=string var1不变	var2=$var1 var1不变
var2=${var1:=string}	var2=string var1=string	var2=$var1 var1不变
var2=${var1:+string}	var2为空 var1不变(也就是说var1也是空)	var2=string var1不变
var2=${var1:?string}	输出格式： shell脚本名：var1=string 并退出shell var2不变	var2=$var1 var1不变

1.var2=${var1:-string}

echo -n "input var1:"
read var1
var2=${var1:-"this is default value"}
echo "var2=$var2"
echo "var1=$var1"

 

2.var2=${var1:=string}

echo -n "input var1:"
read var1
var2=${var1:="this is default value"}
echo "var2=$var2"
echo "var1=$var1"

 

3.var2=${var1:+string}

echo -n "input var1:"
read var1
var2=${var1:+"this is default value"}
echo "var2=$var2"
echo "var1=$var1"

 

 4.var2=${var1:?string}

echo -n "input var1:"
read var1
var2=${var1:?"this is default value"}
echo "var2=$var2"
echo "var1=$var1"