title: Bug while checking for symbols inside of a string?
body: <p>I'm creating a small calculator script and I've got stumbled on a strange bug. Everything seems to work but not when I input anything starting with <code>(</code>. When I do that <code>if</code> gives false and the code inside of <code>else</code> executes. I've tried a lot of ways rewriting how should <code>"$input" =~ [-,+,*,/,\(,\)]</code> look like but nothing worked. Do you have any idea why that's happening and how to solve this bug?</p>
  
  <pre><code>#!/bin/bash
  read -p "Input: " input
  if [[ ! "$input" =~ ^[A-Za-z_]+$ &amp;&amp; "$input" =~ ^[0-9] &amp;&amp; "$input" =~ [-,+,*,/,\(,\)] ]]; then
   (echo $input = $(($input))) 2&gt;- || echo "Please, do not input ..."
  else
   echo "Please, do not input letters or other special symbols and type in only expressions."
  fi
  </code></pre>