title: variable expansion in curly braces
body: <p>This is code</p>
  
  <pre><code>a=''
  b=john
  c=${a-$b}
  echo $c
  </code></pre>
  
  <p>And the output is empty line</p>
  
  <p>And for similar code where first variable is not initialized</p>
  
  <pre><code>b1=doe
  c1=${a1-$b1}
  echo $c1
  </code></pre>
  
  <p>And the output is </p>
  
  <pre><code>doe
  </code></pre>
  
  <p>I do not understand how bash deals with expanding of variables leading to different results.</p>