在循环过程中,有时候需要在未达到循环结束条件时强制跳出循环,像大多数编程语言一样,Shell也使用 break 和 continue 来跳出循环
break命令允许跳出所有循环(终止执行后面的所有循环)。
示例1:
脚本进入死循环直至用户输入数字大于5。要跳出这个循环,返回到shell提示符下,就要使用break命令。
#!/bin/bash
while :
do
echo -n "Input a number between 1 to 5:"
read num
case $num in
1|2|3|4|5) echo "Your number is $num!"
;;
*) echo "You do not select a number between 1 to 5,game is over!"
break
;;
esac
done
脚本运行结果示例:
Input a number between 1 to 5:1
Your number is 1!
Input a number between 1 to 5:10
You do not select a number between 1 to 5,game is over!
在嵌套循环中,break 命令后面还可以跟一个整数,表示跳出第几层循环。
break n
示例2:
如果 var1 等于 2,并且 var2 等于 0,就跳出循环。
#!/bin/bash
for var1 in 1 2 3
do
for var2 in 0 5
do
if [ $var1 -eq 2 -a $var2 -eq 0 ]
then
break 2
else
echo "$var1 $var2"
fi
done
done
如上,break 2 表示直接跳出外层循环。脚本运行结果如下:
1 0
1 5
continue命令与break命令类似,只有一点差别,它不会跳出所有循环,仅仅跳出当前循环。
针对上述示例进行改造。
示例1:
#!/bin/bash
while :
do
echo -n "Input a number between 1 to 5:"
read num
case $num in
1|2|3|4|5) echo "Your number is $num!"
;;
*) echo "You do not select a number between 1 to 5,game is over!"
continue
echo "Game is over!"
;;
esac
done
运行代码发现,当输入大于5的数字时,该例中的循环不会结束,语句
echo "Game is over!"
永远不会被执行。
脚本运行结果如下:
Input a number between 1 to 5:1
Your number is 1!
Input a number between 1 to 5:10
You do not select a number between 1 to 5,game is over!
Input a number between 1 to 5:3
Your number is 3!
Input a number between 1 to 5:
continue 后面也可以跟一个数字,表示跳出第几层循环。
示例2:
#!/bin/bash
NUMS="1 2 3 4 5 6 7"
for NUM in $NUMS
do
Q=`expr $NUM % 2`
if [ $Q -eq 0 ]
then
echo "Number is an even number!"
continue
fi
echo "Found odd number"
done
脚本运行结果如下:
Found odd number
Number is an even number!
Found odd number
Number is an even number!
Found odd number
Number is an even number!
Found odd number