I'm having trouble performing arithmetic expressions in UNIX.

Question

I have the following script:

  #!/bin/sh
  r=3
  r=$((r+5))
  echo r

However, I get this error:

Syntax error at line 3: $ unexpected.

I don't understand what I'm doing wrong. I'm following this online guide to the letter http://www.unixtutorial.org/2008/06/arithmetic-operations-in-unix-scripts/

Answer 1

It works for me (printing 8), if you change echo r to echo $r. What version of sh do you have installed? What unix distribution?

Answer 2

You might want to try the following:

#!/bin/sh  
r=3  
r=$((r + 5))  
echo $r

Answer 3

This sounds fine if you're using bash, but $((r+5)) might not be supported if you're using another shell. What does /bin/sh point to? Have you considered replacing it with /bin/bash if it's available?

Answer 4

The shebang line is your problem. bash is not sh. Change it to #!/bin/bash and it will work. You'll also want echo $r instead of echo r.

Answer 5

For doing maths (including decimals/floats), you can use awkor bc/dc.

awk -vr="$r" 'BEGIN{r=r+5;print r}'

or

echo "$r+5" | bc