The case Statement

General form:
case value in
choice1) commands ;;
choice2) commands ;;

esac

• The case statement lets a shell script choose from a list of alternatives.
• The value portion can come from shell variables, shell-script arguments or command outputs.
• choice1 and choice2 are labels that identify potential choices of action. The shell's pattern matching abilities can be used in the choice labels.
• The ) is used to identify labels, the double semicolon serves to separate one choice from the next and the esac marks the end of the case statement. The double semicolon, however, is not mandatory after the final choice.
• Several commands can be executed for a given choice by separating them with command separators (newline or semicolon).
• The words case and esac MUST come after a command separator. (Say, did you know that already?)
• A choice labeled *) matches any value, so it is often used as the last choice to act as a catchall. (Making it the first choice would cause the first choice to match any value, and all the other choices would never be reached.)
• If no choices match and if there is no catchall choice, then nothing is done.
• The bar symbol | serves as an or operator with which more than one label may be attached to the same response.
  case $animal in
  cat | dog ) echo "$animal is a pet" ;;
  crocodile | snake) echo "$animal is no pet" ;;
  esac