How to increment a variable in bash?

I have tried to increment a numeric variable using both var=$var+1 and var=($var+1) without success. The variable is a number, though bash appears to be reading it as a string.

Bash version 4.2.45(1)-release (x86_64-pc-linux-gnu) on Ubuntu 13.10.

There is more than one way to increment a variable in bash, but what you tried will not work.

You can use, for example, arithmetic expansion:

var=$((var+1))
((var=var+1))
((var+=1))
((var++))

Or you can use let:

let "var=var+1"
let "var+=1"
let "var++"

See also: https://tldp.org/LDP/abs/html/dblparens.html.

var=$((var + 1))

Arithmetic in bash uses $((...)) syntax.