How to test for number smaller than other number

Question

I have a script that goes like this:

while :
do
   Start_Time=$(date +"%s")

      MAIN PROGRAM GOES HERE (CROPPED TO SHORTEN THINGS)

   Run_Time=$(( $(date +"%s") - $Start_Time ))

   if [[ $Run_Time < $Wait_Time ]]
   then
      Delay_Time=$(( $Wait_Time - $Run_Time ))
      sleep $Delay_Time
   else
      echo "Delay exceeded" 
      echo $Run_Time
      echo $Wait_Time
   fi
done

And my problem is that sometimes even if the run time is smaller than the wait time it fails the < test

Here is an output from the last run:

Delay exceeded
Run_Time 4
Wait_Time 30

Answer 1

Try running this code snippet:

if [[ 5 < 20 ]]
then
    echo "5 < 20, as expected"
else
    echo "5 is not less than 20, but why?"
fi

And the output would be 5 is not less than 20, but why?. The answer is that you're using the < conditional expression operator, which is documented as doing:

       string1 < string2
              True if string1 sorts before string2 lexicographically in the current locale.

And your problem is that "20" is lexicographically (or, basically, alphabetically) before "5".

You're looking for:

if (( $Run_Time < $Wait_Time ))

instead - this uses arithmetic evaluation and an arithmetic less-than, which is what you need.