shell_语句

if条件判断语句

有开头有结尾，if...then..elif..then...else ...fi

if ((10>5));then    #两个括号用在if中表示判断大小，后面接分号，then
    echo 10 is greater than 5
elif ((10==5));then
    echo 10 equals 5
else
    echo 5 is greater than 10
fi                  #以反if结尾表示结束

例子：判断目录是否存在，不存在就创建

#!/bin/bash
#make directory if it's not exist
#author narcissus

if [ ! -d ./test2 ];then
		echo create direcotry test2
		mkdir test2
else
		echo directory exists
fi

for 循环

例子：列出普通用户家目录所有文件、目录

#!/bin/bash
#打印用户家目录下的所有文件名
#author narcissus木

cd ~                              #进入家目录
if [ $UID -eq 0 ];then            #判断如果是root用户
		for i in `ls /home/`      #列出所有普通用户
		do
				cd /home/$i       #进入普通用户目录
				for j in `ls`     #循环用户下的文件/目录
				do
						echo $j   #打印
				done
		done
else                              #如果是普通用户
		for j in `ls`             #循环用户下的文件/目录
		do
				echo $j           #打印
		done
		fi

---

while循环

while 条件
do
	action
done

简单的循环

#!/bin/bash
i=0
while [[ $i -lt 10 ]]
do	
	echo "the number is $i"
	((i++))
done

从终端读取数字并计算数字阶乘

#!/bin/bash

read m
i=1
y=1
while [[ $i -lt $m ]]
do
		((i++))
		((y=$y*$i))
done
echo "!m= $y"

实现从指定文件夹读取数据并显示

#!/bin/bash

while read i
do
		echo $i
done < ~/.zshrc

---

until循环

until 条件
do
	action
done

与while差不多

---

case选择

case $arg in
	pattern1)
	action;;
	pattern2)
	action;;
	*)
	action;;
esac

*) 代表不在选择范围内的数据，即其它

选择安装lamp

#!/bin/bash

case $1 in
	apache)
	echo "install apache";;
	mysql)
	echo "install mysql";;
	php)
	echo "install php";;
	*)
	echo "please choose the right package";;
esac

$1 用于读取终端输入的第一个参数

---

select选择

select用于从终端读取选择的数据，与case搭配起来使用

select var in "arg1" "arg2" "arg3" ....
do
	action
done

终端显示选择菜单，并读取所选菜单

#!/bin/bash

PS3="please select the one you want to install: " 
select i in "apache" "mysql" "php"
do
case $i in
		apache)
				echo "install apache"
				;;				
		mysql)
				echo "install mysql"
				;;
		php)
				echo "install php"
				;;
		*) 
				echo "your choise is wrong"
				;;
esac
done

PS3 用来写提示信息