Linux学习笔记-shell(3)

善用判断式

$? && ||

test命令

[root@Dark ~]# test -e /hehehe

检查文件hehehe是否存在，并不会显示任何结果

[root@Dark ~]# test -e hehehe && echo "exist" || echo "Not exist"

关于两个整数之间的判定，例子： test n1 -eq n2;

-eq:两数值相等

-ne:两数值不等

-gt：n1大于n2

-lt：n1小于n2

-ge: n1大于等于n2

-le: n1小于等于n2

判定字符串的数据

test -z string:判定字符串是否为0，若为空字符串，则为true；

test -n string：判定字符串是否非为0，若为空字符串，则为false；

多重条件判定：

-a：两个条件同时成立

-o：任何一个条件成立

！：取反

空格
a.定义变量时, =号的两边不可以留空格

b.if语句 [ 符号的两边都要留空格

c.字符串比较, =两边要留空格
d. if 和then 在同一行 要加；

条件判断式

if [ 条件判断式 ];then
....
fi

#!/bin/bash
read -p "Please input(Y/N):" yn
if [ "$yn" == "Y" ] || [ "$yn" == "y" ];then
        echo "OK,continue"
        exit 0
fi
if [ "$yn" == "N" ] || [ "$yn" == "n" ];then
        echo "Oh,interrupt!"
        exit 0
fi
echo "I don't konw what your choice is" && exit 0

注意空格！

#!/bin/bash
read -p "Please input a num (1-10): " num
num2=`expr $RANDOM % 10 + 1`
if [ "$num" -gt "$num2" ];then
        echo "You win!"
else
        echo "You lose!"
fi

#!/bin/bash
read -p "Please input a num (1-10): " num
num2=`expr $RANDOM % 10 + 1`
if [ "$num" -gt "$num2" ];then
        echo "You win!"
elif [ "$num" -eq "$num2" ];then
        echo "Ping Ju!"
else
        echo "You lose!"
fi

循环（loop）

while [ condition ]

do

     ...

done

s=0
i=0
while [ "$i" != "100" ]
do
        i=$(($i+1))
        s=$(($s+$i))
done
echo $s

for var in con1 con2 con3 ...

do

...

done

for animal in dog cat elephant
do
        echo "There are ${animal}s.."
done

输出结果：

There are dogs..
There are cats..
There are elephants..

#!/bin/bash
network="192.168.0"
for sitenu in $(seq 100 125)
do
        ping -c 1 -w 1 ${network}.${sitenu} &> /dev/null && result=0 || result=1
        if [ "$result" == 0 ];then
                echo "Server ${network}.${sitenu} is UP."
        else
                echo "Server ${network}.${sitenu} is DOWN."
        fi
done

for ((初始值;限制值;执行步长))

do

...

done

#!/bin/bash
read -p "Please input a number:" num
s=0
for ((i=1;i<=$num;i=i+1))
do
        s=$(($s+$i))
done
echo $s

!/bin/bash
for i in {1..22}
do
        echo $i
done