1. 利用判斷符號[]來進行數據的判斷(ex:[ -z "$HOME" ], 判斷$HOME變量是否爲空),常用在if ...... then ......fi 中
需要注意的是:
1. [ ]中的每個組件之間都有空格鍵來分隔
2. [ ]中的變量,最好都用雙引號來設定
3. [ ]中的常數,最好都以單引號或雙引號來設定
ex1:
[ "$HOME" == "$MAILE" ] ------------------>判斷兩者內容是否相同
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 幫我們設定好了的一些指定的變量
$0 $1 $2 $3 $4 ...這些說白了其實就像argv[0] argv[1] argv[2] argv[3] argv[4]一樣,第一個$0,argv[0]都是可執行文件,其他的是命令行參數.
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 判斷字符串是否不爲空,可以省略.
[ -n "$1" ] && echo "The 1st paramter is ==>$1" || exit0
[ -n "$2 "] && echo "The 2nd parameter is ==>$2" || exit0
在命令行執行
[root@linux ~]# ./sh07.sh aaa bbbb
3. 條件判斷式if.....then...fi
當符合某個判斷條件的時候執行
語法格式:
if [ 條件判斷式 ]; then
執行語句
fi
ex:
#!/bin/bash
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin
export PATH
read -p "Please input (Y/N):" yn
if [ "$yn" == "Y"] || [ "$yn" == "y" ]; then
echo "Oh, interrupt!"
exit 0
fi
echo "I don't know what is your choise "&&exit 0
4. 條件判斷式if...then...else...fi
語法格式:
if [ 條件判斷式 ]; then
expression1;
else
expression2
fi
5. 條件判斷式if...then...elif...else...fi
語法格式:
if [ 條件判斷式 ]; then
expression1
elif
expression2
else
expression3
fi