Do math arithmetic on busybox sh

Question

I have string variables MIN and SEC (minute and seconds):

MIN="1"
SEC="34"

I want to do calculations on these:

TOTSEC = MIN*60 + SEC

I tried:

expr $SEC + $MIN * 60

Result:

expr: non-numeric argument

Let it be known I am running busybox on a custom microcomputer and so have no access to bash, bc, and that other solution provides.

Answer 1

busybox uses ash, so you can use:

MIN=1 SEC=34 busybox sh -c 'echo "$(( MIN*60 + SEC ))"'
94

Or with expr:

MIN=1 SEC=34 busybox sh -c 'expr " $MIN" \* 60 + "$SEC"'
94