shell腳本中的邏輯判斷
不帶else
[root@aminglinux-128 ~]# vim if1.sh [root@aminglinux-128 ~]# sh if1.sh Please input your score: 90 You didn't pass the exam. [root@aminglinux-128 ~]# vim if1.sh [root@aminglinux-128 ~]# sh if1.sh Please input your score: 33 You didn't pass the exam.
上例中編輯的腳本
#! /bin/bash read -p "Please input your score: "33 if ((a<60)); then echo "You didn't pass the exam." fi #! /bin/bash read -p "Please input your score: "90 if ((a<60)); then echo "You didn't pass the exam." fi
帶有else
#! /bin/bash read -p "Please input your score: "80 if ((a<60)); then echo "You didn't pass the exam." else echo "Good! You passed the exam." fi #! /bin/bash read -p "Please input your score: "25 if ((a<60)); then echo "You didn't pass the exam." else echo "Good! You passed the exam." fi
腳本執行結果
[root@aminglinux-128 ~]# sh if2.sh Please input your score: 25 You didn't pass the exam. [root@aminglinux-128 ~]# vim if2.sh [root@aminglinux-128 ~]# sh if2.sh Please input your score: 80
帶有elif
vim if3.sh #! /bin/bash read -p "please input your score: "a if ((a<60)); then echo "You didn't pass the exam." elif ((a>=60)) && ((a<85)); then echo "Good! You pass the exam." else echo "Very good! Your score is very high!" fi
腳本輸出結果
[root@aminglinux-128 ~]# vim if3.sh [root@aminglinux-128 ~]# sh if3.sh please input your score: 90 You didn't pass the exam. [root@aminglinux-128 ~]# vim if3.sh [root@aminglinux-128 ~]# sh if3.sh please input your score: 60 You didn't pass the exam.
和文檔相關的判斷
shell腳本中的if用於判斷文檔的屬性，比如判斷是普通文件還是目錄，判斷文件是否有讀、寫、執行權限。
-e：判斷文件或目錄是否存在
-d：判斷是不是目錄以及是否存在
-f：判斷是不是普通文件以及是否存在
-r：判斷是否有讀權限
-w:判斷是否有寫權限。
-x：判斷是否可執行。
使用if判斷時的具體格式：
if [ -e filename ] ; then
command
fi
示例
[root@aminglinux-128 ~]# if [ -d /home/ ];then echo ok; fi ok [root@aminglinux-128 ~]# if [ -f /home/ ];then echo ok; fi
因爲/home/是目錄而非文件，所以並不會顯示ok。
[root@aminglinux-128 ~]# if [ -f /home/ ];then echo ok; fi [root@aminglinux-128 ~]# if [ -f /root/text.txt ];then echo ok; fi [root@aminglinux-128 ~]# if [ -r /root/text.txt ];then echo ok; fi [root@aminglinux-128 ~]# if [ -w /root/text.txt ];then echo ok; fi [root@aminglinux-128 ~]# if [ -x /root/text.txt ];then echo ok; fi [root@aminglinux-128 ~]# if [ -e /root/text.txt ];then echo ok; fi
case邏輯判斷
格式爲
case 變量 in
value1)
command
;;
value2)
command
;;
value3)
command
;;
*)
command
;;
esac
上面的結構中，不限制value的個數，*代表其他值。下面寫一個判斷輸入數值是奇數還是偶數的腳本。
vim case.sh #! /bin/bash read -p "Input anumber: " n a=$[$n%2] case $a in 1) echo "The number is odd." ;; 0) echo "The number is even." ;; *) echo "It's not a number!" ;; esac
腳本中$a的值爲1或0，執行結果如下：
[root@aminglinux-128 ~]# sh case.sh Input anumber: 100 The number is even. [root@aminglinux-128 ~]# sh case.sh Input anumber: 101 The number is odd.
case腳本常用於編寫系統服務的啓動腳本。