• p1.sh two simple commands connected by a pipe
  the parameter of the commands are fixed
• p2.sh introducing variable to make it somewhat flexible
• p3.sh introducing arguments to be used as the parameter of the command
• p4.sh default value for a varible
• p4.1.sh introducing `read'
  introducing $#
  introducing `if'
• p5.sh introducing `case' statement
  introducing the backquote
  ``uname'' is used to make the program adaptive and portable.
• show-arg.sh introducing the `for' loop
  introducing the `expr' command
  introducing the `printf' command
• sum-arg.sh show how to use the `expr' to do arithmetic operations
• sum-arg-bc.sh invoke `bc' to do arithmetic operations
• sum-arg-dc.sh invoke `dc' to do arithmetic operations
• sum-stdin.sh introducing `while'
• sum-to.sh using `while' and 'expr'
• lower.sh using `tr' to rename a file from uppercase to lowercase
  try ``./lower.sh *''