title: Bash string replacement with regex repetition
body: <p>I have a file: filename_20130214_suffix.csv
  I'd like replace the yyyymmdd part in bash. Here is what I intend to do:</p>
  
  <pre><code>file=`ls -t /path/filename_* | head -1`
  file2=${file/20130214/20130215}
  #this will not work
  #file2=${file/[0-9]{8}/20130215/}
  </code></pre>