fib.bash

#!/usr/bin/env bash
set -euo pipefail
PATH=/bin:/sbin

http-request() {
  local domain=$1; shift
  local path=${1:-/}; shift
  local verb=GET

  (
    exec 5<>/dev/tcp/$domain/80
    cat <<-EOF >&5
      $verb $path HTTP/1.1
      User-Agent: bash
      Host: $domain
      Accept: text/html
      Connection: close

    EOF
    cat <&5
  )
}

query-fib() {
  local nth=${1:-0}; shift

  # <li><h4>Binary  Base 2:</h4><div>0</div></li>
  # <li><h4>Hexadecimal Radix 16:</h4><div>0</div></li>
  http-request "www.protocol5.com" "/Fibonacci/$nth.htm" \
    | egrep '<li><h4>[^<]+(Base|Radix) ([[:digit:]]+):</h4><div>([^<]+)</div></li>' \
    | sed -e 's,<[^>]\+>,,g' -e 's,[^[:digit:]]\+\([[:digit:]]\+\):\(.\+\),\1 \2,g'
}

usage() {
  cat <<-EOF
    Usage: $0 [-b base] n-th

    Print n-th fibonacci number in specific base

    -b base : Specific base number, supportted 2,3,5,6,8,10,16,36 (default: 10)
  EOF
}

main() {
  local base=10

  while getopts "b:h" opt; do
    case $opt in
      b)
        case $OPTARG in
          2|3|5|6|8|10|16|36)
            base=$OPTARG
            ;;
          *)
            echo "$0: illegal base number -- $OPTARG"
            usage
            exit 1
            ;;
        esac
        ;;
      h)
        usage
        exit 0
        ;;
      *)
        usage
        exit 1
        ;;
    esac
  done
  shift $(($OPTIND - 1))

  if [[ $# -ne 1 ]]; then
    usage
    exit 1
  fi

  local nth=$1; shift
  local table=$(query-fib $nth)
  if [[ -z "$table" ]]; then
    echo "Cannot pull fibonacci result from internet"
    exit 2
  fi

  while read -r tbase tval; do
    [[ $tbase = $base ]] && echo $tval
  done < <(echo -n "$table")
}

main $@