rand-string

#!/usr/bin/env bash

set -euo pipefail

function main() {
  local POSITIONAL_ARGS=()
  local n_chars=32
  while [ "$#" -gt 0 ]; do
    case "$1" in
    -h | --help)
      print-usage
      exit 0
      ;;
    -n | --num)
      require-named-arg "$@"
      n_chars="$2"
      shift
      shift
      ;;
    -*)
      print-error "Error: Unknown option: $1"
      ;;
    *)
      POSITIONAL_ARGS+=("$1")
      shift
      ;;
    esac
  done

  local first_arg="${POSITIONAL_ARGS[0]:-}"

  if [ -n "$first_arg" ]; then
    n_chars="$first_arg"
  fi

  n_chars="${n_chars^^}"

  if [[ "$n_chars" =~ ^[1-9][0-9]*[KMGT]?$ ]]; then
    rand-str "$n_chars"
  else
    print-error "Error: number argument must be a positive integer with optional suffix (eg. 12, 64, 8K, 1M...)"
  fi

}

function require-named-arg() {
  if [ -z "$2" ]; then
    print-error "Error: Argument for $1 is missing" >&2
  fi
}

function rand-str() {
  openssl rand -base64 "$1" | xargs printf "%s" | head -c "$1"
}

function print-error() {
  echo "$1" >&2
  echo "" >&2
  print-usage >&2
  exit 1
}

function print-usage() {
  local script_name
  script_name="$(basename "$0")"

  echo "Usage: $script_name [...options] [NUM_CHARS]"
  echo ""
  echo "Options:"
  echo "  -h, --help  Display this help message."
  echo "  -n, --num   Number of characters to generate."
  echo "              Default: 32"
  echo ""
  echo "Examples:"
  echo "  $script_name 16"
  echo "  $script_name -n 8 16 # outputs 16 random characters"
  echo "  $script_name -n 32 | xclip -sel clip"
}

main "$@"