Bash scripting 101: Chapter 7:just in CASE you need it

case: case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... esac
    Selectively execute COMMANDS based upon WORD matching PATTERN.  The
    '|' is used to separate multiple patterns.

i don't use case much, i don't know why, it's just never "appealed" to me

"case" is kind of like a "for" and an "if" combined

what they are saying above (in a much convoluted way) is that the below script:

#!/bin/bash

echo -e "using letters type a number between zero and ten\n"
read -e

case "$REPLY" in
        "zero"  )       echo -e "you typed $REPLY which in number is 0\n" ;;
        "one"   )       echo -e "you typed $REPLY which in number is 1\n" ;;
        "two"   )       echo -e "you typed $REPLY which in number is 2\n" ;;
        "three" )       echo -e "you typed $REPLY which in number is 3\n" ;;
        "four"  )       echo -e "you typed $REPLY which in number is 4\n" ;;
        "five"  )       echo -e "you typed $REPLY which in number is 5\n" ;;
        "six"   )       echo -e "you typed $REPLY which in number is 6\n" ;;
        "seven" )       echo -e "you typed $REPLY which in number is 7\n" ;;
        "eight" )       echo -e "you typed $REPLY which in number is 8\n" ;;
        "nine"  )       echo -e "you typed $REPLY which in number is 9\n" 
                        echo -e "$REPLY*$REPLY=$[9*9]\n"  ;;
        "ten"   )       echo -e "you typed $REPLY which in number is 10\n" ;;
        *       )       echo -e "something else was typed, you typed: $REPLY\n" ;;
esac

exit 0

1. #!/bin/bash
   she-bang line

2. echo -e "using letters type a number between zero and ten\n"
   echo..c'mon now..annnnncient!

3. read -e
   HEY! i know "read" and you are doing something weird!!!

   yeah i am, read puts it's "input" into the variable $REPLY if it's not given a variable, personally i always write a variable there, but in this case i'm showing you a way to save some typing

4. case "$REPLY" in
   start the "case/esac" part, use the contents of the variable $REPLY to compare to the patterns

   i quote $REPLY because the rule of thumb i use is, if you compare to quoted, use quoted

5. "zero"   )   echo -e "you typed $REPLY which in number is 0\n" ;;
   if the contents of $REPLY matches "zero" then do the part between the ) and the ;;

   ie, echo -e "you typed $REPLY which in number is 0\n"

   which becomes "you typed zero which in number is 0" followed by a newline

6. "one" to "eight"
   same as "zero" with obvious differances

7. "nine"   )   echo -e "you typed $REPLY which in number is 9\n"
   echo -e "$REPLY*$REPLY=$[9*9]\n" ;; ookay? yer just being silly!

   no..i'm not, i just wanted to show you that the part between ) and ;; can be more than one line and more than one command

   basically: "in case REPLY variable contains "nine", echo (just like zero through eight) but also...

   echo -e "$REPLY*$REPLY=$[9*9]\n"
   
   in other words "nine*nine=$[9*9] newline"
   the $[9*9] part multiplies 9 with 9 and becomes the result, could i have put 81 there? ..sure i could..but then you wouldn't know that you could do maths on the commandline or in a script, would ya?

8. "ten"
   same as "zero" through "eight" with obvious differances

9. *   )   echo -e "something else was typed, you typed: $REPLY\n" ;;
   this is pretty much case's version of "else" from the "if", match everything and what ever you match print out this message, it is crucial that if this is used it be used LAST, case only goes till it finds the FIRST match

unfortunately not much practical use exists for the exact above script (i'm sorry i tend to try to make "useful" learner scripts, in this case i couldn't really figure one out).

with a little thought though, the possibilities are large. In fact, I've noticed that since/during writing this 101-chapter 7 i've started to use case more and more

umm okay but see i don't trust my users, even if i specify use only small letters or CAPS...

ahh well the problem above is one of case sensitivity (always when we use typed input of keywords we need to either check for the different versions). IE at least "ONE", "One", "one"

whilst that could be done: (loosely written..ya'll know the syntax by now)
if test "$REPLY"="ONE"
then
commands here (echo you entered "one")
elif ( "One")
then
commandblock
elif ( "one" )
commandblock
elif (now you do the 3 iterations for two TWO Two)....and then three and then *JEESSEEEEE*
fi

or you could even do a:
REPLY_FIX=`echo -e $REPLY | sed y/ABCDEFGHIJKLMNOPQRSTUVWXYX/abcdefghijklmnopqrstuvwxyz/`

and then search for small (non capital) "one" "two" and so on

they are both kind of clumsly when compared to something along the lines of:(ok.. so the sed solution has some style points for longer comparison lists)

case "$REPLY" in 
 "ZERO" | "Zero" | "zero"  )       echo -e "you typed $REPLY which in number is 0\n" ;;
 "ONE"  | "One"  | "one"   )       echo -e "you typed $REPLY which in number is 1\n" ;;

i'm leaving this chapter "open" (being written) for a while, in "case" i find more examples

w0nderer