I used an ascii painter in the past, but I cannot locate anymore. 

You could do triangle, circle, square and export the art work as
a simple text file... here is what I found so far:

https://www.gridsagegames.com/rexpaint/
https://durdraw.org/
http://www.figlet.org/
https://www.linuxlinks.com/cadubi/
https://github.com/willnode/Ascii-Painter

Update:

I finally found something that work decently on linux. 
It's on Java, but it does the work, it's called jave:

http://jave.de/

It's quite full fledge, with font (figlet) line, circles 
and square, export to text... there will be more art in
here soon!