How to assign array length to a variable in bash

Question

I'm trying to write a simple bash script that adds integers and supplies the sum. I figured the easiest way would be to assign the input to an array. Then traverse the array to perform the summation. I need to use the length of the array in my for loop and cannot figure out how to assign the array length to a variable.

Any help appreciated on the simple script (which I did to learn bash)

#!/bin/bash
# add1 : adding user supplied ints

echo -n "Please enter any number of integers: "
read -a input

echo "Your input is ${input[*]}"
echo "${#input[@]} number of elements"

num = ${#input[@]}   # causing error
for ((i = 0; i < "${num}"; ++i )); do  # causing error
  sum = $((sum + input[$i]))
done

echo "The sum of your input is $sum"

Which yields the errors:

line 10: num: command not found 
line 11: ((: i < :syntax error: operand expected (error token is "< ")

Here is more information on assignment conventions in Bash :) — summea
– summea, Commented May 1, 2013 at 18:10
You say "causing error"; it would be helpful to know what error it is causing. — msw
– msw, Commented May 1, 2013 at 18:16
@msw - Already solved. Thanks for the feedback. The error was: line 10: num: command not found line 11: ((: i < : syntax error: operand expected (error token is "< ") — Dorian
– Dorian, Commented May 1, 2013 at 18:37
In the future, you should include (or edit) that into your question. — msw
– msw, Commented May 1, 2013 at 18:39

msw · Accepted Answer · 2013-05-01 18:15:50Z

10

You just have a syntax error. Remove the space before =:

num = ${#input[@]}   # causing error

becomes:

num=${#input[@]}   # works

Note that if you assign to a variable in bash using the = operator, there MUST NOT be any space before and after the =

Read this entry about Variable Assignment in the Advanced Bash-Scripting Guide

edited May 1, 2013 at 18:15

msw

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answered May 1, 2013 at 18:08

hek2mgl

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2 Comments

Dorian Over a year ago

Thank you. It works. I had the same error throughout the program. And I feel like an idiot. Coming from C++ where that space doesn't matter...

hek2mgl Over a year ago

don't worry about that. every bash coder has once seen this error ;)

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