shell编程之while循环
程序员文章站
2024-03-23 22:45:22
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1.while循环的语法结构如下:
while expression
do
command
done
将测试expression的返回值,如果返回值为真则执行循环体,为假则不执行。例如:
[[email protected] ~]# cat while01.sh
#!/bin/bash
count=5
while [ $count -gt 0 ]
do
echo -n "$count"
let count-=1
done
echo
[[email protected] ~]# sh while01.sh
54321
2.while循环比较经典的用法是按行读取文件,例如:
[[email protected] ~]# cat while02.sh
#!/bin/bash
cat score.txt | while read LINE
do
NAME=`echo $LINE | awk '{print $1}'`
AGE=`echo $LINE | awk '{print $2}'`
SEX=`echo $LINE | awk '{print $3}'`
echo "My name is $NAME,I'm $AGE years old,I'm a $SEX"
done
[[email protected] ~]# sh while02.sh
My name is John,I'm 30 years old,I'm a boy
My name is lily,I'm 40 years old,I'm a girl
3.while的无限循环
主要有3种形式:
方法一:
while (1)
do
command
done
方法二:
while true
do
command
done
方法三:
while :
do
command
done