roman2number.sh

# Convert a number from Roman notation to Arabic.
# Nick Bailey, nickbailey at github.com. 25th July 2023.
# From https://gist.github.com/pysysops/7596f1c0a5c6d14151bbd987a2fb95e5
# Syntax check from the python roman package: https://pypi.org/project/roman/
#
function roman () {
    roman_numerals=$(echo $1 | tr a-z A-Z)

    # Test that it is valid
    [[ "${roman_numerals//[IVXLCDM]/}" == "" ]] || {
        echo "Roman numerals $1 contains invalid characters"
        return 1
    }

    [[ $roman_numerals =~ ^M{0,4}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$ ]] || {
        echo "$roman_numerals isn't a standard number"
        return 2
    }

    # We want to replace all tokens to eventually have
    # all I's, remove new lines and count the characters.
    number=$(
        echo ${roman_numerals} |
        sed -e 's/CM/DCD/g'  -e 's/M/DD/g'  -e 's/CD/CCCC/g' \
            -e 's/D/CCCCC/g'  -e 's/XC/LXL/g'  -e 's/C/LL/g' \
            -e 's/XL/XXXX/g'  -e 's/L/XXXXX/g'  -e 's/IX/VIV/g' \
            -e 's/X/VV/g'  -e 's/IV/IIII/g'  -e 's/V/IIIII/g' |
        tr -d '\n' |
        wc -m
    )

    echo ${number}
}