LiveFire Labs' UNIX Tip, Trick, or Shell Script of the Week

Creating a Menu Using Select

LiveFire Labs' tip from last week explained what the PS2, PS3, and PS4 shell variables were used for.  You may recall that PS3 is used to re-define the prompt string displayed to users when the select command is ready to read a user's menu selection.  This week's tip takes a look at how a robust interactive menu is easily created with the select command.

A frequently-used syntax for the select command is:

select varname in opt1 opt2...optN
do
   case $varname in
      opt1)  command1;;
      opt2)  command2;;
      optN)  commandN;;
   esac
done

opt1-optN represents valid menu options, and command1-commandN represents the commands that will be executed when the corresponding menu option is selected by the user.

The following example is a simple menu that provides the user with system information:

PS3='Select an option and press Enter: '
select i in Date Host Users Quit
do
   case $i in
      Date)  date;;
      Host)  hostname;;
      Users)  who;;
      Quit)  break;;
   esac
done

When executed, this example will display the following:

1) Date
2) Host
3) Users
4) Quit
Select an option and press Enter:

If the user selects 1, the system date is displayed followed by the menu prompt:

1) Date
2) Host
3) Users
4) Quit
Select an option and press Enter: 1
Mon May 5 13:08:06 CDT 2012
Select an option and press Enter:

Pressing the Enter key without making a selection will re-display the menu and menu prompt:

Select an option and press Enter:
1) Date
2) Host
3) Users
4) Quit
Select an option and press Enter:

In the sample code above, notice that PS3 has been re-defined with a custom menu prompt.  If this line of code was omitted the default menu prompt (#?) would be displayed: 

1) Date
2) Host
3) Users
4) Quit
#?