while

• A while statement evaluates a logical expression and continues executing the code inside the while as long as the expression is true.
• The basic format for a while in shell is:

  while [ expression ]
  do
      command
      command
  done
  

• In shell, you may put as many statements inside the while as you would like.
• The do and the done are required, even if there is only one statement to execute.
• Be careful! The square brackets are tricky - you must have the whitespace around them.
• Make sure the expression will change inside the loop! If it does not, you will have an infinite loop.

  Use CTRL-C to exit an infinite loop and end the program.