Bash interpreter keeps giving an error of variable declaration why?

Question

I want to make a simple calculator but this keeps bugging me up why is this happening anyone ??

# !/bin/bash 
  
# Take user Input 
echo "Enter Two numbers : "
read a 
read b 
  
# Input type of operation 
echo "Enter Choice :"
echo "1. Addition"
echo "2. Subtraction"
echo "3. Multiplication"
echo "4. Division"
read ch 
  



if (($ch==1))
then
  res = $((a + b))
elif (($ch==2))
  then
    res = $((a - b))
elif (($ch==3))
  then
    res = $((a * b))
elif (($ch==4))
  then
    res = $((a / b))
else
  echo ERROR
fi
echo Result is $res

i tried the case statement but same.

Please take a look at [How do I format my posts using Markdown or HTML?](https://stackoverflow.com/help/formatting). — Cyrus, Apr 01 '23 at 10:39
In shell, (unquoted) spaces are delimiters. So, there must be no space around the `=` in an assignment. `var = val` is not interpreted as an assignment but the command `var` with the arguments `=` and `val`. — M. Nejat Aydin, Apr 01 '23 at 10:55
Please add a **valid** shebang (`#!/bin/bash`) to your script, then paste it at http://www.shellcheck.net/ and try to implement all the recommendations made there. — Cyrus, Apr 01 '23 at 11:07
And consider a `case` statement instead of a series of if-else's to improve your code readability and maintainability. — Ed Morton, Apr 01 '23 at 12:13
Also see [What is the rationale behind variable assignment without space in bash script](https://stackoverflow.com/q/56910878/4154375). — pjh, Apr 01 '23 at 12:40
In fact, there technically is no separate assignment *statement* in shell, at least syntactically. Assignments are *words* in (pre)command position that contain at least one `=`. If a line consists only of assignment words and no command, then the assignments take place in the current shell instead of the environment of the command. — chepner, Apr 01 '23 at 17:58

score 0 · Answer 1 · answered Apr 01 '23 at 13:54

In general, it is a good idea to let shellcheck look at your script before you post it. In this case, shellcheck will inform you:

Line 1:
# !/bin/bash
 ^-- SC1115 (error): Remove spaces between # and ! in the shebang.
 
Line 21:
  res = $((a + b))
      ^-- SC2283 (error): Remove spaces around = to assign (or use [ ] to compare, or quote '=' if literal).
 
Line 24:
    res = $((a - b))
        ^-- SC2283 (error): Remove spaces around = to assign (or use [ ] to compare, or quote '=' if literal).

et cetera. I left out the informational messages.

And with the corrections suggested by shellcheck, your calculator works fine.

Oh, and please do not post images of text. See XKCD.

Bash interpreter keeps giving an error of variable declaration why?

1 Answers1