CSH Calculator Script

Shell Programming and Scripting
1

Using the C Shell, I'm building a script that will compute simple mathematical computations (addition, subtraction, multiplication, division). The user will enter two integers (operands) on the command line separated by the operation (operator) they wish to perform.

Example of the command line would be as follows: ./scriptname 5 minus 2

I have that part working perfectly. Where I'm running into a problem is the following:

1) If the any of the operands or operator are missing from the command line I want to print an error

2) If the user enters an invalid operator (not +, -, %, X) the script shall will print an error)

I've attached my script below. If you have any recommendations for the above two issues your help would be greatly appreciated. Thank you!

if ( $2 =~ "plus" ) then
        @ c = $1 + $3
        echo "The sum is: $c"

else if ( $2 =~ "minus" ) then
        @ c = $1 - $3
        echo "The difference is: $c"

else if ( $2 =~ "div" ) then
        @ c = $1 / $3
        echo "The quotient is: $c"

else if ( $2 =~ "times" ) then
        @ c = $1 * $3
        echo "The product is: $c"

else if ( ( $2 !~ "plus" || $2 !~ "minus" ) && ( $2 !~ "div" || $2 !~ "times" ) ) then
        echo "You have entered an invalid operation"

else
        echo "You are missing an operand or operator"
endif
3

That last statement looks over-complicated to me I think:

if ( $2 == "string" ) then
...
else if ( $2 == "other" ) then
...
else
        echo "operator is invalid or missing"
endif

But this would be easier with a case I think:

switch ($2)
     case plus:
       ...
       breaksw
     case minus:
       ...
       breaksw
     ...
     default:
       echo "Bad or missing operator"
       breaksw
     endsw
1 Like
4

Thank you, Carona. I'll try that but would like to learn how to do it both ways. I'm learning UNIX through a book I bought and this was one of the exercises. Clearly - I'm not very good at it.

5

Csh is not recomended: Csh Programming Considered Harmful

I'm more of a BASH scripter anyway.
BASH Programming - Introduction HOW-TO

Hope this helps

6

I'm using it as part of an exercise in the book. In this respect, I want to use it (or tcsh)

7

I told you both ways.

CSH is not UNIX, it's a nonstandard language which was popular in the early 80's(it supported "fancy" things like line editing!) but has only clung to a weird, tenuous life since then -- mostly through it being forcefed to new students through badly out-of-date textbooks. Occasional old systems still run it to use scripts old enough to be having mid-life crises. Kind of the UNIX equivalent of qbasic.

These days a proper UNIX shell has all the same advantages with none of the notorious design flaws.

1 Like
8

I generally refuse to use csh and its derivatives for reasons already mentioned in this thread... But, I think you want to change:

else if ( $2 =~ "times" ) then
        @ c = $1 * $3
        echo "The product is: $c"

else if ( ( $2 !~ "plus" || $2 !~ "minus" ) && ( $2 !~ "div" || $2 !~ "times" ) ) then
        echo "You have entered an invalid operation"

else
        echo "You are missing an operand or operator"
endif

to something like:

else if ( $2 =~ "times" ) then
        @ c = $1 * $3
        echo "The product is: $c"

else    echo "You have entered an invalid operation"
        exit 2
endif

and I think you want to add something like:

if ( $# < 3 ) then
        echo "You are missing an operand or operator"
        exit 1
endif

before the code you showed us. I have not tested any of these suggestions, but they should get you a little bit closer to what you're trying to do.

If you want to learn about UNIX and Linux (and BSD) system shell programming, I strongly suggest you get a different book that describes ksh , bash , or some other shell that is based on Bourne shell syntax.

Good luck.

1 Like
9

Thanks to all who helped me with it. I think I've got it working. On to the next challenge :frowning: