Syntax error for (( $word = "y" || $word = ""Y" ))

Question

This is my shell script where i check whether the entered word is y or n; if any of these match then it will print an appropriate message.

 #! /bin/bash

read word

if (( $word = "y" || $word = "Y" ))
then    
    echo "YES"
elif (( $word = "n" || $word = "N" ))
then    
    echo "NO"
fi

But when I run this code then it will give me a run-time error.

Solution.sh: line 5: ((: y = y || y = Y : attempted assignment to non-variable (error token is "= Y ")
Solution.sh: line 8: ((: y = n || y = N : attempted assignment to non-variable (error token is "= N ")

Answer 1

You want [[ ... ]], not ((...)) (which is for arithmetic expressions)

#!/bin/bash

read word

if [[ $word = "y" || $word = "Y" ]]
then    
    echo "YES"
elif [[ $word = "n" || $word = "N" ]]
then    
    echo "NO"
fi

You can simplify this using pattern matching rather than strict equality testing

if [[ $word = [Yy] ]]
then
    echo "YES"
elif [[ $word = [Nn] ]]
then
    echo "NO"
fi

Or use a standard case statement

case $word in
  [Yy]) echo "YES" ;;
  [Nn]) echo "NO" ;;
esac