shell脚本语法

条件测试：test [

-测试一个条件是否成立，

• 如果结果为真，则结果=0
• 如果结果为假，则结果=1

python@ubuntu:~/1004$ var=2python@ubuntu:~/1004$ test $var python@ubuntu:~/1004$ echo $?0python@ubuntu:~/1004$ test $var -gt 5python@ubuntu:~/1004$ echo $?1

或者：

（注意： 两边加空格）

python@ubuntu:~/1004$ [ $var -gt 1 ]python@ubuntu:~/1004$ echo $?0

语法错误：

python@ubuntu:~/1004$ [ $s1 = $s4 ]bash: [: hello: 需要一元表达式需要加"" :  [ "$s1" = "$s4" ]

if/then/elif/else/fi

实现分支控制

• 判断是否事目录-d (-f文件)
• fi：判断if结束的关闭标签

#! /bin/shif [ -d ~/Desktop ]; then        echo "Desktop is dir"        echo "dimples"fi

source t2.sh

• ：空命令（不做任何事，执行总是真）
• read命令：等待用户输入一行字符串，存到shell变量中

#! /bin/shecho "it is morniing? yes or no"read YES_OR_NOif [ "$YES_OR_NO" = "yes" ]; then        echo "早上好"elif [ "$YES_OR_NO" = "no" ]; then        echo "中午好"else        echo "sorry"        exit 1fiexit 0

python@ubuntu:~/1004$ vi t3.shpython@ubuntu:~/1004$ chmod a+x t3.shpython@ubuntu:~/1004$ ./t3.shit is morniing? yes or noyes早上好

case/esac

• 类似C语言的switch/case语句
• esac表示case语句块的结束

#! /bin/shecho "is it morning"read YES_OR_NOcase "$YES_OR_NO" inyes|y|Yes|YES)        echo "早上好";;[nN]*)        echo "中午好";;*)        echo "sorry"        exit 1;;esacexit 0

• source执行结果会传递给shell,shell退出了
• 必须用chmod：

python@ubuntu:~/1004$ chmod a+x t4.shpython@ubuntu:~/1004$ ./t4.sh

case语句的例子可以在系统服务的脚本目录 /etc/init.d中找到。这个目录下都是启动脚本程序。

循环语句

for/do/done

• 类似于foreach循环
• 反引号：``执行命令

#! /bin/shfor FRUIT in apple pear banana; do        echo "I like $FRUIT" done

python@ubuntu:~/1004$ source t5.shI like appleI like pearI like banana

while/do/done

#! /bin/shecho "输入密码："read PWDwhile [ "$PWD" != "111111" ]; do        echo "Sorry, try again"        read PWDdone

python@ubuntu:~/1004$ source t6.sh输入密码：1Sorry, try again2Sorry, try again111111

通过算数运算控制循环的次数:

• 用户最多可已输入5次密码，输入正确直接结束

#! /bin/shecho "请输入密码"read PWDCOUNTER=1while [ "$COUNTER" -lt 6 ]; do        if [ "$PWD" != "123" ]; then                #break                if [ "$COUNTER" -eq 5 ]; then                        echo "输入错误，没有机会啦"                else                        echo = "输入错误，再来一次"                        read PWD                fi        else                echo "输入成功"                break        fi        COUNTER=$(($COUNTER+1))done