#!/bin/bash

function printl() {
    function yell() { echo "$0: $*" >&2; } # print script path and all args to stderr
    function die() { yell "$*"; exit 111; } # same as yell() but non-zero exit status
    function showUsage() {
        # Desc: Display script usage information
        # Usage: showUsage
        # Input: none
        # Output: stderr
        yell "USAGE:";
        yell "printl [int] [int] ([path])";
        yell ""
        yell "EXAMPLE:"
        yell "printl 5 17 somefile.txt"
    }; # Display information on how to use this script.
    function main() {
        # Desc: Prints ranges of lines
        # Usage: printl [int] [int] [path]
        # Version: 0.0.1
        # Example: printl 5 17 somefile.txt  # prints lines 5-17
        # Depends: Bash 5.1.16
        start="$1";
        end="$2";

        # Require first two args be integers
        re='^[0-9]+$';
        if [[ ! "$start" =~ $re ]]; then
            showUsage;
            die "FATAL:First argument (start line number) not an integer:$(declare -p start)";
        fi;
        if [[ ! "$end" =~ $re ]]; then
            showUsage;
            die "FATAL:Second argument (end line number) not an integer:$(declare -p end)";
        fi;

        # Require between 2 and 3 arguments are provided
        if [[ $# -ge 4 ]]; then
            showUsage;
            die "FATAL:Too many arguments:$#";
        fi;
        if [[ $# -le 1 ]]; then
            showUsage;
            die "FATAL:Too few arguments:$#";
        fi;

        # Handle 3 argument case (int int file)
        if [[ $# -eq 3 ]] && [[ -f "$3" ]]; then
            # Use specified file
            input="$3";
        elif [[ $# -eq 3 ]] && [[ ! -f "$3" ]]; then
            showUsage;
            die "FATAL:Third argument not a file.";
        fi;

        # Handle 2 argument case (int int)
        if [[ $# -eq 2 ]]; then
            # Use stdin
            input="-"
        fi;

        # Print lines
        tail -n+${start} "$input" | head -n$((end - start + 1));

    }; # main program

    ( must main "$@" ); 
};