(eshell-gather-process-output):

Set process-connection-type nil for all but the first element of a
pipeline.  (Bug#1388)

1 files changed, 21 insertions, 5 deletions

diff --git a/lisp/eshell/esh-proc.el b/lisp/eshell/esh-proc.el
index 25d9dd64663..39fea83cd8d 100644
--- a/lisp/eshell/esh-proc.el
+++ b/lisp/eshell/esh-proc.el
@@ -250,11 +250,27 @@ Used only on systems which do not support async subprocesses.")
     (cond
      ((fboundp 'start-process)
       (setq proc
-            (apply 'start-process
-                   (file-name-nondirectory command) nil
-                   ;; `start-process' can't deal with relative
-                   ;; filenames
-                   (append (list (expand-file-name command)) args)))
+            ;; Bug#1388.  Some commands (eg bc) check isatty to decide
+            ;; whether they are being called interactively.
+            ;; A normal shell pipeline has:
+            ;; first: stdin tty , stdout pipe
+            ;; rest : stdin pipe, stdout pipe
+            ;; last : stdin pipe, stdout tty
+            ;; We have:
+            ;; first: stdin tty , stdout tty
+            ;; last : stdin pipe, stdout pipe
+            ;; In other words, the first and last elements have the
+            ;; wrong kind of stdout.  (Perhaps this does not matter much...)
+            ;; FIXME which is better for the first element:
+            ;; tty/tty (as now), or pipe/pipe?
+            (let ((process-connection-type
+                   (unless (and eshell-in-pipeline-p
+                                (not (eq eshell-in-pipeline-p 'first)))
+                     process-connection-type)))
+              (apply 'start-process
+                     (file-name-nondirectory command) nil
+                     ;; `start-process' can't deal with relative filenames
+                     (append (list (expand-file-name command)) args))))
       (eshell-record-process-object proc)
       (set-process-buffer proc (current-buffer))
       (if (eshell-interactive-output-p)