title: get sub string in shell script
body: <p>if I have a string like <code>some/unknown/amount/of/sub/folder/file.txt</code> how can I get only the the <code>file.txt</code> sub string, remove the front part, while the <strong>length is unknown</strong>.</p>
  
  <p>thank you </p>
  
  <p>EDIT: file name could be any length, and sub folders could be any levels.</p>