Question

I need to make a bash script that takes user input and does some validation.

The input is small. I just need to get a user choice “yes” or “no” and a file path and make sure the input is indeed a filepath and that he entered yes or no.

How can I validate the user input?

Answer 1

from your bash prompt type

help read

---

example:
step 1.

pete@ruthie ~ $ read -p “Yes or No :” ANSWER

Yes or No :Yes

pete@ruthie ~ $ echo $ANSWER

Yes

step 2.

case $ANSWER in 
    Y* | y* ) echo "ANSWER is yes" ;; 
    N* | n*) echo ANSWER is no;; 
     *) echo "Unclear Response" ;; 
esac

ANSWER is yes

Or all on one line:

case $ANSWER in Y* | y* ) echo "ANSWER is yes" ;; N* | n*) echo ANSWER is no;; *) echo "Unclear Response" ;; esac

ANSWER is yes

So something vaguely like::

   read -p "Enter File Name :" FILE_TO_CHECK 

    if [ ! -e "$FILE_TO_CHECK" ]; then 
        echo -e "There is no file called $FILE_TO_CHECK \n please check spelling"
    else
        echo  "Congratulations found $FILE_TO_CHECK. "
         ls -lah $FILE_TO_CHECK
         read -p "Process $FILE_TO_CHECK ? Y or N : PROCEED
           case $PROCEED in
             Y* | y*)
##call function or system command to do something with this data
               foo $FILE_TO_CHECK

             ;;
            * )
             echo -e "Note $USER\n No action taken by $0 on $FILE_TO_CHECK"
             ;;
            esac

    fi

---

The test command is your friend. You really need to learn its ways ASAP.

help [

and

help test

The “help bashthing” command is a great quick reminder.

see also: the Advanced Bash Scripting Guide (ABS)
http://tldp.org/LDP/abs/html/

FWIW:
This is a very simple example and wont accommodate much in the way of unexpected user input.
I would probably call functions for each step of this as then I could conditionally represent the user with another chance.

The case tests nested like this is plain ugly 🙂 === hard to get neat and read later

There are other ways to achieve all this try zenity for a GTK style GUI.

The A.B.S is excellent but dont try to eat it all at once !