bash shell notes (5)

1. Judgment statement

#!/bin/bash

read -p "please input (Y/N)" yn
if [ "$yn" == "Y" ] || [ "$yn" == "y" ]; then
        echo "ok,continue!"
        exit 0
fi
if [ "$yn" == "N" ] || [ "$yn" == "n" ]; then
        echo "no,interrupt!"
        exit 0
fi

        echo "sorry,i dont know what is your choice" && exit 0

2、case ...esac

for example:

#!/bin/bash
case $1 in
        "hello")
                echo "hello,how are you!"
                ;;
        "")
                echo "you must input someword"
                ;;
        *)
                echo "Usage $0 {hello}"
                ;;

esac

3、function fname() {

                            block

}

4. Cycle  

while [ condition ]

do

        program paragraph

done

example

while [ "$yn" != "YES" ] && [ "$yn" != 'yes' ]

do 

        read -p "please input yes/YES to stop the program" yn

done

Similarly

until [ condition ]

do

        program paragraph

 done

5. Already know how many times to loop

for ((initial value; limit value; execution step))

do 

        block

done

6. Script tracking and debugging

sh [-nvx] scripts.sh

Parameter -n: do not execute the script, only query the syntax

-v: output the script to the screen before executing the script

-x: display the used script to the screen