UNIX script coding HW question

i am trying to write a script code in unix that will:

1. The problem statement, all variables and given/known data:
   display following menu to user:
   (A) Add
   (B) Subtract
   (C) Multiply
   (D) Divide
   (E) Modulus
   (F) Exponentiation
   (G) Exit
   Then ask user for choice (A-F). After taking users choice ask user for two numbers and
   perform chosen operation on those two numbers. The program should keep asking
   for choice / numbers unless user chooses �G� for exit.

2. Relevant commands, code, scripts, algorithms:

3. The attempts at a solution (include all code and scripts):

i tried everything to write this code i couldnt

4. Complete Name of School (University), City (State), Country, Name of Professor, and Course Number
   school name: Senaca college, Toronto, Canada, Name of Professor: peter wheeler, and Course Number: Tech 154

OK, what exactly have you tried? Post your tries here and we can tell you why they don't work or what you do wrong.

bakunin

thats what ive tried

echo -n "Enter first number " 
read a 
echo -n "Enter second number " 
read b 
if [ $x == 'A' -o $x == 'a' ] ; then 
  c=$(( a + b )) 
fi 
if [ $x == 'B' -o $x == 'b' ] ; then 
  c=$(( a - b )) 
fi 
if [ $x == 'C' -o $x == 'c' ] ; then 
  c=$(( a * b )) 
fi 
echo "The answer is $c"

Ok i see you had did a read -p 'Please type ation:' x , that is not visible here .

You can either make sure the provided char inputs are non-caps, or use regex to catch both at once.
1) Make it small (is this posix?)

x=A
x=${x,,}
[ $x = a ] && echo "Add"

2) Or use Regex:

x=a
[ $x = [aA] ] && echo "Add"

Use either 1. or 2., this will save you from using if [ $x == 'B' -o $x == 'b' ] ; then for each of the A-F.

3) For menus or comparing 1 value with diffrent options, its quite easier to use a case statement

case $x in
a)    echo "do add" ;;
b)    echo "do sub" ;;
esac

4) Could use Regex here too (= instead)

case $x in
a|A)    echo "do add" ;;
[bB])    echo "do sub" ;;
esac

edit: 5. Quotes:
I'd rather make the quotes around the variables, than around the letters.
If the variable is empty, or contains a special char (like arrow-up) it will produce and error message, rather than just not execute (as in not true ; not matching).

Hope this helps

Does that really work?
IMHO the standard demands

if [[ $x == [aA] ]]
then
 echo "Add"
fi

(Also I replaced the quick && by an if statement.) This and the equivalent case statement use shell globbing (not RE).

[root@dell ~]# x=A
[root@dell ~]# [ $x = [aA] ] && echo "Add" 
[root@dell ~]# [ $x == [aA] ] && echo "Add" 
[root@dell ~]# [[ $x = [aA] ]] && echo "Add" 
Add
[root@dell ~]# [[ $x == [aA] ]] && echo "Add" 
Add
[root@dell ~]# echo $SHELL
/bin/bash

However:

[root@dell ~]# x=A
[root@dell ~]# x=${x,,}
[root@dell ~]# [ $x = a ] && echo "Add"
Add
[root@dell ~]# 

So yes, for the REGEX you need the double brackets.
BTW: bad behaviour example as i was running it as root

Edit: Yes, for anything more complex than a simple single yes/no requires a standard if-statement like:

if [ $x -ge 100 ] || [[ "$x" == [aA] ]]
then    echo "Great"
else    echo "Low"
fi

BTW: The only 'place' i actualy use == (as it wont work properly with a single) is with PHP.
All of both the shells (sh,bash) i came across worked well with a single =.

EDIT2:
Just read (once more) the 'man bash', and beeing in the homework section i must say:
-> Better get used to use the proper syntax right from the start!