Subtract two variables in Bash

Question

I have the script below to subtract the counts of files between two directories but the COUNT= expression does not work. What is the correct syntax?

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Answer 1

White space is important, expr expects its operands and operators as separate arguments. You also have to capture the output. Like this:

COUNT=$(expr $FIRSTV - $SECONDV)

but it's more common to use the builtin arithmetic expansion:

COUNT=$((FIRSTV - SECONDV))