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.

Accepted Answer

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

Answer 3

An answer that is not limited to the OP's case

The title of the question leads people here, so I decided to answer that question for everyone else since the OP's described case was so limited.

I finally settled on writing a function.

int(){ printf '%d' ${1:-} 2>/dev/null || :; }

int(){ expr 0 + ${1:-} 2>/dev/null||:; }

int(){ expr ${1:-} : '[^0-9]*\([0-9]*\)' 2>/dev/null||:; }

# This is a combination of numbers 1 and 2
int(){ expr ${1:-} : '[^0-9]*\([0-9]*\)' 2>/dev/null||:; }

If you want to get a non-zero status code on non-int, remove the ||: (aka or true) but leave the ;