Listing 7 is_valid_date

function is_valid_date
{

    set -A DAYS_TO_MONTH NA 0 31 59 90 120 151 181 212 243 273 304 334 365

    #---------------
    # Get the input.
    #---------------

    integer Y=$1
    M=$2
    integer D=$3

    #-------------------------------------------
    # If necessary, convert month to an integer.
    #-------------------------------------------

    if ! is_integer $M 2> /dev/null
    then
        M=$(month_to_int $M)
    fi

    #--------------------
    # Validate the input.
    #--------------------

    if ! is_integer $Y 2> /dev/null || (( $Y < 0 ))
    then
        echo "invalid year"
        return 1
    fi

    if (( $M < 1 )) || (( $M > 12 ))
    then
        echo "invalid month"
        return 1
    fi

    if ! is_integer $D 2> /dev/null || (( $D < 1 )) || (( $D > 31 ))
    then
        echo "invalid day"
        return 1
    else
        if (( $D > $((${DAYS_TO_MONTH[$((M+1))]}-${DAYS_TO_MONTH[$M]})) ))
        then
            if (( $M == 2 )) && is_leap_year $Y && (( $D == 29 ))
            then
                : # OK
            else
                echo "invalid day"
                return 1
            fi
        fi
    fi

    return 0
}
# End Listing 7