Question

I have a script which asks the user the following question:

read -p "Input time duration of simulation in HH:MM:SS format" -e Time

Now how do I ensure the user entered the correct form for $Time
before the variable $Time is actually used?

Answer 1

I assume you need to check hour < 24, minutes < 60, seconds < 60?

read -p "Input time duration of simulation in HH:MM:SS format " -e Time

while :; do
  if [[ $Time =~ ^([0-9]{2}):([0-9]{2}):([0-9]{2})$ ]]; then
    if (( BASH_REMATCH[3] < 60 ))\
       && (( BASH_REMATCH[2] < 60 ))\
       && (( BASH_REMATCH[1] < 24 )); then
       break
    fi
  fi
  read -p "Wrong format. Please use the HH:MM:SS format " -e Time
done

# Do something with $Time