Attempt on basic input validation and functional programming in a POSIX shell

Question

In spite of all the POSIX shell disadvantages, I am still sticking with it and I love its portability.

Recently, I was searching for a way of code re-use, which turns out to be structured programming and input validation = Yes, in a POSIX shell script.

---

Let me begin with the simpler.

is_integer() + is_exit_code()

is_integer ()
{
    case "${1#[+-]}" in
        (*[!0123456789]*) return 1 ;;
        ('')              return 1 ;;
        (*)               return 0 ;;
    esac
}

is_exit_code ()
{
    is_integer "$1" &&
    case "$1" in
        ([+-]*) return 1 ;;
    esac &&
    [ "$1" -le 255 ]
}

---

Here, I continue on with further chained functions.

print_error() + print_error__exit()

print_error ()
{
    if ! { [ $# -eq 2 ] && [ -n "$1" ] && [ -n "$2" ]; } then
        printf '%b\n' "Some longer error message."
        exit 1
    fi
    printf '%b\n' \
        "${color_red}Error occurred$tput_reset" \
        "Error heading: $color_yellow$1$tput_reset" \
        "Error message: $2"
        
} >&2

print_error__exit ()
{
    if ! { [ $# -eq 2 ] && [ -n "$1" ] && [ -n "$2" ]; } &&
       ! { [ $# -eq 3 ] && [ -n "$1" ] && [ -n "$2" ] && is_exit_code "$3" && [ "$3" -ge 1 ]; } then
        printf '%b\n' "Some longer error message."
        exit 1
    fi
    print_error "$1" "$2"
    exit "${3:-1}"
} >&2

---

So, in this bare example, the chains go up like this:

1. print_error__exit () 🠆 print_error ();

2. print_error__exit () 🠆 is_exit_code () 🠆 is_integer ().

---

Despite I am quite confident, these examples work as they should, one never knows, a maybe different point of view would shed a different light on my process.

Answer 1

Your code looks nice. I give some additional advice.

1. You can debug by calling the source command in your terminal (REPL).
2. You can divide the common codes and the main codes by writing the source in the main code.
3. Take care of an enormous number. The number 99999999999999999999999999999999999999999999999999, and so on.
4. The action of writing some function is not functional programming but structured programming. The functional programming paradigm is like the idea of stream and pipe. Then, if you do not know functional programming, you may practice functional programming.