shell编程

分支语句

if语句

#!/bin/bash
read -p "input two number": a b
if [ $a -lt $b ]
then
        echo "$a < $b"
elif [ $a -eq $b ]
then
        echo "$a = $b"
else
        echo "$a > $b"
fi

root@lisheng-VMware20-1:/home/lisheng/Desktop/script# bash hello.sh 
input two number:20 10
20 > 10

case语句

read -p "input a number:" num
case "$num" in
        1)
                echo "num is 1"
                ;;
        2)
                echo "num is 2"
                ;;
        [3-9])
                echo "num is $num"
                ;;
        *)
                echo "error"
esac

root@lisheng-VMware20-1:/home/lisheng/Desktop/script# bash case_2.sh
input a number:1
num is 1

循环语句

while循环

while true
do
        uptime >>/tmp/demo.log
        sleep 3
done

for循环

for ((i=1;i<=3;i++))
do
        echo "i=$i"
done

root@lisheng-VMware20-1:/home/lisheng/Desktop/script# bash for.sh 
i=1
i=2
i=3

函数

function demo()
{
        echo "call demo"
        echo $1 $2
        return 100
}
demo zhangsan lisi


root@lisheng-VMware20-1:/home/lisheng/Desktop/script# bash func.sh 
call demo
zhangsan lisi
root@lisheng-VMware20-1:/home/lisheng/Desktop/script# echo $?
100