I was thinking to re-implement xeyes in terminal, so drawing a circle is essential. It’s not hard, not even in using Bash plus bc, but I don’t really see the point to reinvent the eyes, therefore I stopped just after I was able to primitively draw a circle, like the following one:

            11111111222222222
         1111               2222
      111                       222
     11                           22
   11                               22
  11                                 22
 11                                   22
 1                                     2
 1                                     2
33                                     44
 3                                     4
 3                                     4
 33                                   44
  33                                 44
   33                               44
     33                           44
      333                       444
         3333               4444
            33333333444444444

You can view the codes in this Gist, which also includes a couple of variations. The one above uses sin and cos functions. In that Gist, there is another approach by using r2-x2, that also gives acceptable results.

Because bc is called many times, the speed is noticeable, at least to me. If using bc’s programming features and returning a series of calculated numbers at once, I am sure it would run much faster. But since I am not interested in continuing, so I didn’t do anything.