shell scripts学习(二)

1. 利用判断符号[]来进行数据的判断(ex:[ -z "$HOME" ], 判断$HOME变量是否为空),常用在if ...... then ......fi 中

需要注意的是:

1. [ ]中的每个组件之间都有空格键来分隔

2. [ ]中的变量,最好都用双引号来设定

3. [ ]中的常数,最好都以单引号或双引号来设定

ex1:

[ "$HOME" == "$MAILE" ] ------------------>判断两者内容是否相同

ex2:

[root@linux ~] vim sh06.sh

#!/bin/bash

PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin

export PATH

read -p "Please input (Y/N):" yn

[ "$yn" == "Y" -o "$yn" == "y" ] && echo "OK, continue" && exit 0

[ "$yn" == "N" -o "$yn" == "n" ] && echo "Oh, interrupt!" && exit 0

echo "I don't konw what is your choise " && exit 0

2. shell scripts 帮我们设定好了的一些指定的变量

$0 $1 $2 $3 $4 ...这些说白了其实就像argv[0] argv[1] argv[2] argv[3] argv[4]一样,第一个$0,argv[0]都是可执行文件,其他的是命令行参数.

ex:

[root@linux ~] vim sh07.sh

#!/bin/bash

PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin

export PATH

echo "The script name is ==> $0"

# -n 判断字符串是否不为空,可以省略.

[ -n "$1" ] && echo "The 1st paramter is ==>$1" || exit0

[ -n "$2 "] && echo "The 2nd parameter is ==>$2" || exit0

在命令行执行

[root@linux ~]# ./sh07.sh aaa bbbb

3. 条件判断式if.....then...fi

当符合某个判断条件的时候执行

语法格式:

if [ 条件判断式 ]; then

执行语句

fi

ex:

#!/bin/bash

PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin

export PATH

read -p "Please input (Y/N):" yn

if [ "$yn" == "Y"] || [ "$yn" == "y" ]; then

echo "Oh, interrupt!"

exit 0

fi

echo "I don't know what is your choise "&&exit 0

4. 条件判断式if...then...else...fi

语法格式:

if [ 条件判断式 ]; then

expression1;

else

expression2

fi

5. 条件判断式if...then...elif...else...fi

语法格式:

if [ 条件判断式 ]; then

expression1

elif

expression2

else

expression3

fi