Dockerfile

#printf
RUN printf '#!/bin/bash\n\
echo hello world from line 1\n\
echo hello world from line 2\n'\
> /tmp/hello
## or you can use >>

RUN cat /tmp/hello

#echo
RUN echo -e '#!/bin/bash\n\
echo hello world from line 1\n\
echo hello world from line 2'\
>> /tmp/hello

echo -e:

-e     enable interpretation of backslash escapes
-E     disable interpretation of backslash escapes (default)

But -e didn't work for me, so I went with printf. Also, I tacked on an extra trailing newline, in order to cat the file out without scribbling over the terminal