shell脚本--语法篇

例如：字符串比较

#!/bin/bash
read data
test "$data" == "hello" //注意等号两边有空格  或者 [ $data == "hello" ]
echo $? //上一条命令的运行结果，成功为0，失败为1

例如：两数比较大小

#!/bin/bash
data=200
[ $data -eq 100 ]
echo $?
[ $data -lt 100 ]
echo $?
[ $data -le 100 ]
echo $?
[ $data -gt 100 ]
echo $?
[ $data -ge 100 ]
echo $?

例如：测试与、非逻辑运算

#!/bin/bash
read data
if [ "$data" -eq 100 ];then
    echo "100"
elif [ "$data" -eq 200 ];then
    echo "200"
else
    :  //  :为空命令，该命令不做任何事
fi

#!/bin/bash
read data
[ "$data" -eq 100 ] && {   //成立执行花括号里面，否则执行括号外

    echo "yes"
    exit 0
}
echo "no"

#!/bin/bash
read data
[ "$data" -eq 100 ] || {  //不成立执行花括号里面，否则执行括号外

    echo "yes"
    exit 0
}
echo "no"

#!/bin/bash
read val
case "$val" in
    start | -s | -start | -START )
        echo "start"
        ;;
    ‘stop‘ )
        echo "stop"
        ;;
    ‘*‘ )
        echo "*"
        ;;
esac

写法一：

#!/bin/bash

//for i in {1..100}

for i in {a..z}
do
   echo "$i"
done

运行结果: 打印a...z的字母

写法二：

#!/bin/bash
for(( i=0;i<=100;i++ ))
do
   echo "$i"
done

运行结果: 打印1...100的数字

求1~100 间的偶数的和

#!/bin/bash
sum=0
ret=0
for i in {1..100}
do
    let ret=i%2
    if [ $ret -eq 0 ];then
        let sum+=i
    fi
done
echo $sum

运行结果：2550