GH echo seems to let -e argument through. Trying to force core-utils' echo.
# Dockerfile to setup beremiz_public_dist build container
FROM ubuntu:focal
ENV TERM xterm-256color
COPY provision_focal64.sh .
RUN ./provision_focal64.sh
ENV LANG en_US.UTF-8
ENV LANGUAGE en_US:en
ENV LC_ALL en_US.UTF-8
ARG UNAME=devel
ENV UNAME ${UNAME}
ARG UID=1000
ARG GID=1000
RUN groupadd -g $GID $UNAME
RUN useradd -m -u $UID -g $GID -s /bin/bash $UNAME
# easy to remember 'build' alias to invoke main makefile
ARG OWNDIRBASENAME=beremiz_public_dist
ENV OWNDIRBASENAME ${OWNDIRBASENAME}
RUN /bin/echo -e '#!/bin/bash\nmake -f /home/'$UNAME'/src/'$OWNDIRBASENAME'/Makefile $*' > /usr/local/bin/build
RUN chmod +x /usr/local/bin/build
USER $UNAME
RUN mkdir /home/$UNAME/build /home/$UNAME/src