title: use of flags in bash script
body: <p>Scripts in linux start with some declaration like : </p>
  
  <p><code>#!/bin/bash</code></p>
  
  <p>Correct me if I am wrong : this probably says which shell to use. </p>
  
  <p>I have also seen some scripts which say : </p>
  
  <p><code>#!/bin/bash -ex</code></p>
  
  <p>what is the use of the flags -ex </p>