Support redirects with empty commands.

* gash/eval.scm (exp->thunk): Return 'noop' if 'exp' is '#f'.
* tests/50-redirect-clobber.sh: New file.
* tests/50-redirect-clobber.stdout: New file.
* Makefile.am (FULL_TESTS): Add tests/50-redirect-clobber.sh.

Co-authored-by: Timothy Sample <samplet@ngyro.com>

Makefile.am

@@ -214,6 +214,7 @@ FULL_TESTS =                                    \
   tests/50-redirect-sed.sh                      \
   tests/50-redirect-space.sh                    \
   tests/50-redirect-in-out.sh                   \
+  tests/50-redirect-clobber.sh                  \
   tests/60-function.sh                          \
   tests/60-function-at.sh                       \
   tests/60-subst.sh                             \

gash/eval.scm

@@ -1,5 +1,6 @@
 ;;; Gash -- Guile As SHell
-;;; Copyright © 2018 Timothy Sample <samplet@ngyro.com>
+;;; Copyright © 2018, 2019 Timothy Sample <samplet@ngyro.com>
+;;; Copyright © 2018, 2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 ;;;
 ;;; This file is part of Gash.
 ;;;
@@ -52,7 +53,10 @@
       (_ `(,op ,fd ,field)))))
 
 (define (exp->thunk exp)
-  (lambda () (eval-sh exp)))
+  ;; XXX: See comment in `exps->thunk'.
+  (if exp
+      (lambda () (eval-sh exp))
+      noop))
 
 (define (exps->thunk exps)
   ;; XXX: It probably makes more sense to exclude '#f' expressions at

tests/50-redirect-clobber.sh

@@ -0,0 +1,4 @@
+echo foo > /tmp/bar$$
+cat /tmp/bar$$
+> /tmp/bar$$
+cat /tmp/bar$$

tests/50-redirect-clobber.stdout

@@ -0,0 +1 @@
+foo