How to convert string to integer in UNIX

Question

I have d1="11" and d2="07". I want to convert d1 and d2 to integers and perform d1-d2. How do I do this in UNIX?

d1 - d2 currently returns "11-07" as result for me.

Answer 1

The standard solution:

 expr $d1 - $d2 

You can also do:

echo $(( d1 - d2 )) 

but beware that this will treat 07 as an octal number! (so 07 is the same as 7, but 010 is different than 10).

Answer 2

Any of these will work from the shell command line. bc is probably your most straight forward solution though.

Using bc:

$ echo "$d1 - $d2" | bc 

Using awk:

$ echo $d1 $d2 | awk '{print $1 - $2}' 

Using perl:

$ perl -E "say $d1 - $d2" 

Using Python:

$ python -c "print $d1 - $d2" 

all return

4