shell循环结构之while循环

while循环

1)

while CONDITION; do
statement
statement
<改变循环条件真假的语句>
done

编写脚本，计算1---100的和

#!/bin/bash
#

sum=0
i=1

while [ $i -le 100 ]; do
let sum=$sum+$i
let i=$i+1
done

echo $sum

2)

while true; do
statement
statement
done

#!/bin/bash
#

while true; do
read -p "请输入你的选择：" choice
if [ $choice == "q" ]; then
break
fi
done

#!/bin/bash
#

while true; do
uptime
sleep 3
done

3)

while read line; do
statement
statement
done < file

#!/bin/bash
#

bash_num=0
nologin_num=0

while read line; do
sh_name=$(echo $line | awk -F: '{print $7}')
case $sh_name in
/bin/bash)
let bash_num=$bash_num+1
;;
/sbin/nologin)
let nologin_num=$nologin_num+1
;;
esac
done < /etc/passwd

echo $bash_num
echo $nologin_num

util循环：

util CONDITION; do
statement
statement
done

条件为假时，执行循环，条件为真时，结束循环