Bash Shell Script – select 迴圈

select

select 的語法如下,他是一個無限迴圈會一直重覆讓使用者輸入資料並執行 do done 內的 script .

select name [in list]
do
statements that can use $name...
done

下面這個範例就是使用 select 這一無限迴圈,使用者可以選擇 1) A , 2) B , 3) C , 4) D ,並執行 do done 內的 script,需要使用 ctrl+c 來終止程式的執行.

root@ubuntu:~# vi select.sh
#!/bin/bash
select i in A B C D
do
echo your choice is ${i}
done

root@ubuntu:~# ./select.sh 
1) A
2) B
3) C
4) D
#? 1
your choice is A
#? 2
your choice is B
#? 3
your choice is C
#? ^C

if

可以配合 if 來使用.

if condition
then
statements
[elif condition
then statements...]
[else
statements]
fi

修改一下程式,這樣就不需要按 ctrl+c 來終止程式的執行.選擇 5) exit 即可以離開.

root@ubuntu:~# vi select.sh
#!/bin/bash
select i in A B C D exit
do
if [ "${i}" == "exit" ]; then
 exit
else
 echo your choice is ${i}
fi
done

root@ubuntu:~# ./select.sh 
1) A
2) B
3) C
4) D
5) exit
#? 1
your choice is A
#? 5

case

也可以配合 case 來使用.

case expression in
pattern1 )
statements ;;
pattern2 )
statements ;;
...
esac

修改一下程式.

#!/bin/bash
select i in A B C D exit
do
case $i in
    A) echo your choice is A;;
    B) echo your choice is B;;
    C) echo your choice is C;;
    D) echo your choice is D;;
    exit) exit;;
esac
done

root@ubuntu:~# ./select.sh 
1) A
2) B
3) C
4) D
5) exit
#? 1
your choice is A
#? 5

PS3

定義 PS3 ,可以讓原本 case 的輸入提示字元 #? 變成自定的輸入提示字元.

#!/bin/bash
PS3="Select (1-5): "
select i in A B C D exit
do
case $i in
    A) echo your choice is A;;
    B) echo your choice is B;;
    C) echo your choice is C;;
    D) echo your choice is D;;
    exit) exit;;
esac
done

root@ubuntu:~# ./select.sh 
1) A
2) B
3) C
4) D
5) exit
Select (1-5): 1
your choice is A
Select (1-5): 5