Sniped used to edit configuration files using a template like file variable=value

edit.sh

#APPLICATION_ENV_SETTINGS is a file containing settings in format file variable=value

print_msg "Applying custom settings"
tr -d '\r' < "${APPLICATION_ENV_SETTINGS}" | while IFS='= ' read TARGETFILE VARNAME VARVALUE; do
        # Don't declare variables here, you are in a sub-shell that dies
        # when exitting while.
    if [[ ! $TARGETFILE =~ ^\ *# && -n $TARGETFILE ]]; then
        VARVALUE="${VARVALUE%%\#*}"    # Del in line right comments
        VARVALUE="${VARVALUE%%*( )}"   # Del trailing spaces
        VARVALUE="${VARVALUE%\"*}"     # Del opening string quotes
        VARVALUE="${VARVALUE#\"*}"     # Del closing string quotes
                # not uncomenting with sed because we may end with multiple variables (if first instance is commented and a second uncommented exits)
                try_run "Setting $(basename ${TARGETFILE}): ${VARNAME}" sed -i "s|^[ ]*${VARNAME}[ ]*=.*|${VARNAME}=$(eval echo "\"$VARVALUE\"")|" "${APPLICATION_DIST_PATH}/${TARGETFILE}"
                if ! grep -q "^[ ]*${VARNAME}[ ]*=.*" "${APPLICATION_DIST_PATH}/${TARGETFILE}" ; then
                        lastline=$(tail -n 1 "${APPLICATION_DIST_PATH}/${TARGETFILE}"; echo x); lastline=${lastline%x}
                        if [ "${lastline: -1}" != $'\n' ]; then
                                echo >> "${APPLICATION_DIST_PATH}/${TARGETFILE}"
                        fi
                        try_run "    Actually had to add above at the end of file" echo
                        echo "# Automatically added" >> "${APPLICATION_DIST_PATH}/${TARGETFILE}"
                        echo "${VARNAME}=\"${VARVALUE}\"" >> "${APPLICATION_DIST_PATH}/${TARGETFILE}"
                fi
    fi
done