Eshell: copy output of visual commands

[Frank Fischer <frank-fischer@shadow-soft.de>]

I want to use certain commands from eshell that have colourized output.
Because eshell is not a full terminal emulator it relies on ansi-term
to execute these commands. However, when the command has finished the
ansi-term buffer is deleted. Hence, if a "visual" commands does not
wait for user input but just prints something to the screen and then
exits immediately, its output is lost (e.g. I use mercurial with
colourized output declared as visual commands, but commands like "hg
log" just print something to the screen and then exit). The idea is to
copy the final output of the commands, i.e. the content of the terminal
buffer after the command has finished, back to the eshell buffer. This
gives eshell a behaviour quite close to standard terminal emulators in
these situations. For those who are interested, I use the following
modifications of eshell (the changed lines are marked):


```
(defadvice eshell-exec-visual (around fifr (&rest args) activate)
  "Store insertion point for result of visual command."
  (let* (eshell-interpreter-alist
         (interp (eshell-find-interpreter (car args)))
         (program (car interp))
         (args (eshell-flatten-list
                (eshell-stringify-list (append (cdr interp)
                                               (cdr args)))))
         (term-buf
          (generate-new-buffer
           (concat "*" (file-name-nondirectory program) "*")))
         (eshell-buf (current-buffer)))
    (save-current-buffer
      (switch-to-buffer term-buf)
      (term-mode)
      (set (make-local-variable 'term-term-name) eshell-term-name)
      (make-local-variable 'eshell-parent-buffer)
      (setq eshell-parent-buffer eshell-buf)
      ;; CHANGED
      (make-local-variable 'eshell-visual-point)
      (setq eshell-visual-point
            (with-current-buffer eshell-buf
              (set-marker (make-marker) (1- (point)))))
      ;; CHANGED
      (term-exec term-buf program program nil args)
      (let ((proc (get-buffer-process term-buf)))
        (if (and proc (eq 'run (process-status proc)))
            (set-process-sentinel proc 'eshell-term-sentinel)
          (error "Failed to invoke visual command")))
      (term-char-mode)
      (if eshell-escape-control-x
          (term-set-escape-char ?\C-x))))
  nil)

(defun fifr/eshell-copy-visual-output (shell-buf proc-buf)
  "Copy result of visual command back to the shell buffer."
  (and (buffer-live-p shell-buf)
       (buffer-live-p proc-buf)
       (prog1 t
         (let ((txt (with-current-buffer proc-buf
                      (buffer-substring (point-min) (point-max))))
               (mrk (with-current-buffer proc-buf
                      eshell-visual-point)))
           ;; Remove useless empty lines at the end
           (save-match-data
             (setq txt (substring 
                        txt 0
                        (string-match "^[[:space:]\n]*\\'"txt)))) 
           (with-current-buffer shell-buf
             (save-excursion
               (goto-char (1+ mrk))
               (set-marker mrk nil)
               (insert txt)))))))

(defadvice eshell-term-sentinel (around fifr (proc string) activate)
  "Maybe copy the content of the term buffer back to the shell buffer."
  (let ((proc-buf (process-buffer proc)))
    (when (and proc-buf (buffer-live-p proc-buf)
               (not (eq 'run (process-status proc)))
               (= (process-exit-status proc) 0))
      (if (eq (current-buffer) proc-buf)
          (let ((buf (and (boundp 'eshell-parent-buffer)
                          eshell-parent-buffer
                          (buffer-live-p eshell-parent-buffer)
                          eshell-parent-buffer)))
            (if buf
                (switch-to-buffer buf))))
      ;; CHANGED
      (if (with-current-buffer proc-buf
            (fifr/eshell-copy-visual-output 
             eshell-parent-buffer
             proc-buf)) 
          (kill-buffer proc-buf)
        (with-current-buffer proc-buf
          (switch-to-buffer proc-buf)
          (local-set-key "q"
                         #'(lambda ()
                             (interactive)
                             (kill-buffer (current-buffer)))))))))
      ;; CHANGED
```

Best regards,
Frank