[Sh] failed script timer

s=$(date +%s)
sleep 3s
e=$(date +%s)

diff=`expr ${e} - ${s}`
if [ ${diff} -lt 30 ]; then
  echo $diff
  exit 1
fi

https://qastack.kr/ubuntu/892604/meaning-of-exit-0-exit-1-and-exit-2-in-a-bash-script

bash 스크립트에서 종료 0, 종료 1 및 종료 2의 의미

https://stackoverflow.com/questions/7119130/less-than-operator-in-if-statement-results-in-no-such-file-or-directory

Less than operator '<' in if statement results in 'No such file or directory'

https://stackoverflow.com/questions/8385627/subtract-two-variables-in-bash

Subtract two variables in Bash