Support standard input, output and error streamsfeature/stdout-stderr-stream

* doc/lispref/streams.texi: Update doc
* lisp/simple.el (external-standard-input): New function
* src/fns.c (external-standard-input-read-char,
  external-standard-input-read-line): New functions
* src/print.c: (external-standard-output,
  external-standard-input): New functions

1 files changed, 15 insertions, 0 deletions

diff --git a/lisp/simple.el b/lisp/simple.el
index a757876328b..17697f9be2b 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -8718,6 +8718,21 @@ to capitalize ARG words."
       (capitalize-region (region-beginning) (region-end))
     (capitalize-word arg)))
 
+(defvar external-standard-input-pushback nil
+  "Pushback character for `external-standard-input'.")
+
+(defun external-standard-input (&optional char)
+  "Read a character from the system standard input.
+
+If CHAR is non-nil, then do not read but return CHAR
+on the next invocation."
+  (if char
+      (setq external-standard-input-pushback char)
+    (if (eq nil external-standard-input-pushback)
+        (external-standard-input-read-char)
+      (let ((rtn external-standard-input-pushback))
+        (setq external-standard-input-pushback nil)
+        rtn))))
 
 
 (provide 'simple)