Bash function to set or append to a Java settings file.

set_or_append_java_config.sh

function set_or_append_java_config() {
    local FILE=$1
    local KEY=$2
    local VALUE=$3

    if grep -q "^${KEY}=" "${FILE}"; then
       sed -i -e "s#^\\(${KEY}=\\).*"'$'"#\\1${VALUE}#" "${FILE}"
    else
       echo "${KEY}=${VALUE}" >> "${FILE}"
    fi
}

Based on the solution here: https://stackoverflow.com/questions/13456564/append-or-modify-keys-in-conf-files-using-sed-bash-one-liner