title: Bash regex =~ operator
body: <p>What is the operator <code>=~</code> called? Is it only used to compare the right side against the left side?</p>
  
  <p>Why are double square brackets required when running a test?</p>
  
  <p>ie. <code>[[ $phrase =~ $keyword ]]</code></p>
  
  <p>Thank you</p>