#!/bin/bash
set -eu -o pipefail

number=$1

# Test that it is valid
[[ "${number//[0-9]/}" == "" ]] || \
    { echo Number ${number} contains invalid characters ; \
    exit 1 ;}

# First we convert the number to a Roman Numeral unary representation
# then we replace appropriate chunks of tokens and end up with a Roman Numeral
# representation.
roman_numerals=$(
    printf "%.sI" $(seq 1 ${number}) |
    sed 's/IIIII/V/g' |
    sed 's/IIII/IV/g' |
    sed 's/VV/X/g' |
    sed 's/VIV/IX/g' |
    sed 's/XXXXX/L/g' |
    sed 's/XXXX/XL/g' |
    sed 's/LL/C/g' |
    sed 's/LXL/XC/g' |
    sed 's/CCCCC/D/g' |
    sed 's/CCCC/CD/g' |
    sed 's/DD/M/g' |
    sed 's/DCD/CM/g'
)

echo ${number} is ${roman_numerals}