Hi

I am trying to use expr to do simple arithmetic. I read user input (like 2+3) from the keyboard and store it in a variable. When I use expr to perform the calculation it needs me to make a space between the numbers and the operand. Another thing is that when I multiply it gives me an error saying "expr: Syntax error".
Here is my code:

while true
do
echo "Enter Arithmetic Calculation:"
read calc
echo `expr $calc`
done



Please help as usual. Thanks in advance!

i have never used expr... another way of doing is
read calc
echo $((calc))

oh see if this works
read calc
echo `expr $((calc))`

I offer two alternatives: 1) you can pass the calculation to bc without modifying the input, i.e.
2) in bash you can try the arithmetic expansion, i.e.
If you really want to use expr, take in mind that the multiplication operator must be escaped as \*. So you have to parse the input and transform the arithmetic operators to escape them and/or to add blank spaces, but this is a little more tricky and if you really don't need it, I suggest one of the two methods mentioned above.

expr is a little choosy about its parameter, you must space them correctly, and in the case of a * you have to escape it to stop the shell from treating it as a wildcard, which is why you get the syntax error.

If you're using the bash shell try this instead of the expr line.

edit:

I see others have recommended $(( )) rather than $[ ] and as $(( )) appears to be listed in the manual pages for arithmetic you're probably better off sticking with that. Anyone know where I've picked up $[ ] from? Is it old bourne shell syntax or something?

Hi.
cheers, makyo

Ahh, its an old bashism is it. I guess I'm showing my age again.
Thanks makyo.

Also an excerpt from the Advanced Bash Scripting Guide, Example 8.2 Using Arithmetic Operations

Thanks guys!

I used the line echo `expr $((calc))` and it worked perfectly fine that I didn't even had to bother escaping the * character. Thank you all!!