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9. Case
Thecase statement saves going through a whole set of
if .. then .. else statements. Its syntax is really quite
simple:
talk.sh
#!/bin/sh echo "Please talk to me ..." while : do read INPUT_STRING case $INPUT_STRING in hello) echo "Hello yourself!" ;; bye) echo "See you again!" break ;; *) echo "Sorry, I don't understand" ;; esac done echo echo "That's all folks!"
Okay, so it's not the best conversationalist in the world; it's only an example!
Try running it and check how it works...
$ ./talk.sh
Please talk to me ...
hello
Hello yourself!
What do you think of politics?
Sorry, I don't understand
bye
See you again!
That's all folks!
$
The syntax is quite simple:
The
case line itself is always of the same format, and it
means that we are testing the value of the variable INPUT_STRING.
The options we understand are then listed and followed by a right bracket,
as hello) and bye).
This means that if
INPUT_STRING matches hello then that section
of code is executed, up to the double semicolon.
If INPUT_STRING matches bye then the goodbye
message is printed and the loop exits. Note that if we wanted to exit
the script completely then we would use the command exit
instead of break.
The third option here, the *), is the default catch-all
condition; it is not required, but is often useful for debugging purposes
even if we think we know what values the test variable will have.
The whole case statement is ended with esac (case backwards!)
then we end the while loop with a done.
That's about as complicated as case conditions get, but they can be a very useful and powerful tool. They are often used to parse the parameters passed to a shell script, amongst other uses.
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