How do you handle multiple validation rules on varied user input?

Question

I'm using a Bash script to prompt users for several variables before continuing. If I want to create static validation rules and execute them on user inputs in an "a la carte" fashion, how would I go about doing that?

Example:

function q1 () {
  echo "Do you have an answer?"
  read input
  # I know this is wrong but should get the idea across
  chkEmpty($input)
  chkSpecial($input)
}

function chkEmpty () {

    if [[ $input = "" ]]; then
      echo "Input required!"
      # Back to Prompt
    else
      # Continue to next validation rule or question
    fi
}

function chkSpecial () {

    re="^[-a-zA-Z0-9\.]+$"
    if ! [[ $input =~ $re ]]; then
      echo "Cannot use special characters!"
      # Back to prompt
    else
      # Continue to next validation rule or question
    fi
}

function chkSize () {
    etc...
}

etc...

Answer 1

Functions get their arguments in $1, $2, etc. Also, in shell they're called w/o parentheses, so your code is almost right.

Your function syntax isn't quite right either: You either use parens or the word function. Finally, you can return a result (which works like a process's exit code) with return.

chkEmpty() {
    if [[ "$1" = "" ]]; then
      echo "Input required!"
      return 1 # remember: in shell, non-0 means "not ok"
    else
      return 0 # remember: in shell, 0 means "ok"
    fi
}

Now you can call it like this:

function q1 () {
  echo "Do you have an answer?"
  read input
  chkEmpty $input && chkSpecial $input # && ...
}

Obviously, you'll need to add some code to deal with the invalid input, e.g., by prompting again or aborting the script. If you use while/until and if to check the function's return values, and reprompt or exit.