I keep Getting error: 'arr[$i] is not a valid identifier' on bash script

Linear Data Structure

3/21/23, 9:47 AM

I'm practicing Fibonacci series on bash script with arrays and for loop but I got this error

jrnl6T2.sh: line 10: `arr[$i]': not a valid identifier

Here is .sh file

#! /bin/bash

read -p "Enter term: " term

arr[0]=0
arr[1]=1
for (( i=2; i<$term; i++))
do

    arr[$i]= expr $((arr[$i-2]+arr[$i-1]))
    
done

for (( j=0; j<$term; j++ ))
do
    echo ${arr[$j]}
    
done

As I'm a beginner so not sure why I am getting this error. I have google this problem also but did not find appropriate solution. I am using ubuntu 20.04.3

0 + 0

bash

scripts

Score:2

Ubuntu

FedKad

3/21/23, 10:10 AM

You are doing two wrong things in the expression calculation statement:

You have put a space character after the = sign. You cannot use whitespace before or after the equals sign.
expr is a command. To capture and assign its output, you need to enclose it in $(), like this:
```
arr[i]=$(expr $((arr[i-2]+arr[i-1])))
```
or
```
arr[i]=$(expr ${arr[i-2]} + ${arr[i-1]})
```
^{Please note that the expr command in the first case does nothing; the $(()) construct calculates the expression.}

However, I suggest you do Bash arithmetic operations using the let command.

Your script can be corrected like this:

#!/bin/bash
read -p "Enter term: " term
let arr[0]=0
let arr[1]=1
for (( i=2; i<term; i++ ))
do
  let arr[i]=arr[i-2]+arr[i-1]
done
for (( j=0; j<term; j++ ))
do
  echo ${arr[j]}
done

Another alternative (which is equivalent to the let command, but I would not prefer) is this:

arr[i]=$(( arr[i-2] + arr[i-1] ))

0 + 0

Linear Data Structure

3/21/23, 11:00 AM

can you explain why did you change `arr[$i]` with `arr[i]`. I have checked, both term gives the same output

FedKad

3/21/23, 11:34 AM

I think this is coming from Korn Shell. See end of section 6.4.1 at https://docstore.mik.ua/orelly/unix3/korn/ch06_04.htm

Elon Musk

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EN: I keep Getting error: 'arr[$i] is not a valid identifier' on bash script

TH: ฉันได้รับข้อผิดพลาด: 'arr[$i] ไม่ใช่ตัวระบุที่ถูกต้อง' ในสคริปต์ทุบตี

RO: Continui să primesc eroare: „arr[$i] nu este un identificator valid” în scriptul bash

RU: Я продолжаю получать ошибку: «arr [$ i] не является допустимым идентификатором» в сценарии bash

VI: Tôi liên tục gặp lỗi: 'arr[$i] không phải là mã định danh hợp lệ' trên tập lệnh bash

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