title: sed command is not working in shell script when a variable is passed as parameter
body: <p>I have following codes in my shell script</p>
  
  <pre><code>a=$(cat php1.php | grep 'hello')
  echo $a
  sed -i 's/'"$a"'/world/' php1.php
  </code></pre>
  
  <p>The variable is getting printed correctly. However when i pass it as parameter to sed command, sed command is not working.</p>
  
  <p>where am i going wrong?</p>