title: how to increase part of a variable in linux
body: <p>Hi guys I have the following function in linux script. </p>
  
  <pre><code>#!/bin/bash
  function add1{
     echo $1
     var1=$1
     echo input + 1 is [$var1+1]
  }
  add 1
  </code></pre>
  
  <p>I want to take the input and add 1. So if the input was input_1 i want to return input_2.
  My code is currently printing input_1+1. I think this is because I am trying to add a integer to a string but i'm not sure of any other way I could do this. 
  Can someone please point me in the right direction?</p>