Input validation in a bash script

Question

I've got the basics of bash scripting (I think anyways), and i'm trying to move on to more advanced stuff.

I am trying to write a script that will perform input validation (the user must input either yes or no) and i'm trying to do this by combining a function and an if then else statement.

This is what i'm working on so far.

#!/bin/bash
func ()
{ 
    echo "Enter yes or no:"
    read var1
}

if [ $var1 != yes ] || [ $var1 != no ]
then
    func
else
    echo "I'm glag you said $var1"
fi

exit 0

I know that i'm using the wrong if then else operator/syntax, but I can't find the correct syntax threw googling.

I want it to run the function if var1 is either equal to yes or no, so the user can't input something else.

Why `if` and not `while` to insist until the input is correct? — manatwork, Mar 02 '14 at 17:20
If your script is complex enough to warrant careful input validation, it is certainly ripe for a real scripting language, like Python, Ruby, or Perl. — vonbrand, Mar 02 '14 at 17:34
Agree with vonband. If you are doing something complex, try Python if it is available. Also, [avoid bashisms](http://unix.stackexchange.com/questions/24146/avoiding-bash-isms-in-shell-scripts). Use /bin/sh instead. — Gregor, Mar 02 '14 at 18:14

cuonglm · Answer 1 · 2014-12-16T15:56:26.507

1

I think you have some wrong logic in your script. You should refer to X Tian's link in above comment to learn more about bash.

Here's a quick fix for you script:

func() {
  echo -n "Enter yes or no: "
  read var1
}

while true; do
  func

  if [[ $var1 == "yes" ]] || [[ $var1 == "no" ]]
  then
    printf "I'm glag you said %s\n" "$var1"
    break
  fi
done

exit 0

edited Dec 16 '14 at 15:56

answered Mar 02 '14 at 17:27

cuonglm

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score 0 · Answer 2 · edited Apr 16 '19 at 13:44

0

#!/bin/bash
func()
{
    echo -n "Enter yes or no : "

    read confirmation
}   
confirmation="$(echo ${confirmation} | tr 'A-Z' 'a-z')"
if [ "$confirmation" == yes ] || [ "$confirmation" == no ]; then
    echo "I am gladd you said $confirmation"
else
    func
fi
exit 0

edited Apr 16 '19 at 13:44

Rui F Ribeiro

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answered Mar 02 '14 at 17:32

klerk

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2
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15

Input validation in a bash script

2 Answers2