title: What is the difference between "$a" and $a in unix
body: <p>For example:</p>
  
  <pre><code>#!/bin/sh
  a=0
  while [ "$a" -lt 10 ]
     b="$a"
     while [ "$b" -ge 0 ] do
        echo -n "$b "
       b=`expr $b - 1`
     done
     echo
     a=`expr $a + 1`
  done*
  </code></pre>
  
  <p>The above mentioned script gives the answer in triangle while with out the double quotes, it falls one after the other on diff lines.</p>