I want to eval a buffer and send the result to a new buffer. How do I "send" the result of the eval-buffer function to the content of a new buffer? here my attempt:
(set-buffer (get-buffer-create "test")) ; create new buffer
(let ((value (eval-buffer)) .... ; how to put this inside the new buffer?
This evaluates the contents of buffer evaluate-me and prints the value of each toplevel form to the buffer output:
(eval-buffer "evaluate-me" (get-buffer-create "output"))
Do C-h f eval-buffer to see the documentation that explains why this works. The second argument to eval-buffer is named PRINTFLAG, of which the docstring says:
PRINTFLAG controls printing of output:
A value of nil means discard it; anything else is stream for print.
The slightly confusing thing about this is Emacs's unusual concept of what counts as an "output stream". Buffers, markers (locations in buffers), and the echo area can all be treated as "streams", as can any function that takes a character argument. Look up the docstrings of the print function or standard-output variable for more info.
The more general way to make things happen inside another buffer is the macro with-current-buffer. Unlike set-buffer, it takes care of restoring the original context cleanly even if errors happen in the wrapped code.
(with-current-buffer (get-buffer-create "output")
(insert "some text"))
Your value calculation appears wrong: since set-buffer will switch to the new buffer, eval-buffer will evaluate the contents of the new empty buffer. My understanding is that you want to evaluate the contents of the previous buffer and print its value in the new buffer:
(let ((value (eval-buffer)))
(set-buffer (get-buffer-create "test"))
(print value))
If you want the new buffer to be visible to the user, replace set-buffer with switch-to-buffer.
