the case shell AND example of using case to create a menu-优快云博客

本文介绍了Shell脚本中case命令的基本用法及其与if/elif命令的区别。通过两个实例展示了如何使用case命令进行多分支选择，并结合heredocument创建菜单选项供用户选择。

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14.5.8 The `case` Command

The case command is a multiway branching command used as an alternative to if/elif commands. The value of the case variable is matched against value1, value2, and so forth, until a match is found. When a value matches the case variable, the commands following the value are executed until the double semicolons are reached. Then execution starts after the word esac (case spelled backward).

If the case variable is not matched, the program executes the commands after the *), the default value, until ;; or esac is reached. The *) value functions the same as the else statement in if/else conditionals. The case values allow the use of shell wildcards and the vertical bar (pipe symbol) for ORing two values.

FORMAT

case variable in

value1)

    command(s)

    ;;

value2)

    command(s)

    ;;

*)

command(s)

    ;;

esac

Example 14.30.

(The Script)

    #!/bin/bash

    # Scriptname: xcolors



1   echo -n "Choose a foreground color for your xterm window: "

    read color

2   case "$color" in

3   [Bb]l??)

4        xterm -fg blue -fn terminal &

5        ;;

6   [Gg]ree*)

        xterm -fg darkgreen -fn terminal &

        ;;

7   red | orange)              # The vertical bar means "or"

        xterm -fg "$color"  -fn terminal &

        ;;

8   *)

        xterm -fn terminal

        ;;

9   esac

10  echo  "Out of case command"

Creating Menus with the `here document` and `case` Command

The here document and case command are often used together. The here document is used to create a menu of choices that will be displayed to the screen. The user will be asked to select one of the menu items, and the case command will test against the set of choices to execute the appropriate command.

Example 14.31.

(From the .bash_profile File)

    echo "Select a terminal type:  "

1   cat <<- ENDIT

        1) unix

        2) xterm

        3) sun

2   ENDIT

3   read choice

4   case "$choice" in

5   1)   TERM=unix

         export TERM

         ;;

    2)   TERM=xterm

         export TERM

         ;;

6   3)   TERM=sun

         export TERM

         ;;

7   esac

8   echo "TERM is $TERM."