New variable: *child-env*.

This specifies the environment to be used for executing
programs.

* stream.c (open_subprocess, run): Check *child-env* variable and if
other than t, then install the environment before execvp.
In the spawn-based version of run, we save and restore the
environment around the spawn call, if *child-env* is in
effect.

* sysif.c (child_env_s): New symbol variable.
(exec_wrap): If *child-env* is other than t, then save the
environment in a list, and install the specified environment
before calling execvp. If that function returns, restore the
environbment.

* sysif.h (child_env_s): Declared.
(child_env): New macro.

* tests/018/process.tl: New tests.

* txr.1: Documented.

* stdlib/doc-syms.tl: Updated.

1 files changed, 14 insertions, 0 deletions

diff --git a/tests/018/process.tl b/tests/018/process.tl
index 07ecfb64..a1970738 100644
--- a/tests/018/process.tl
+++ b/tests/018/process.tl
@@ -25,3 +25,17 @@
     (mtest
       (fcmd (let ((*stdout* *stdnull*)) (sh "echo foo"))) ""
       (fcmd (let ((*stderr* *stdout*)) (sh "echo foo 1>&2"))) "foo\n")))
+
+(mtest
+  (let ((*child-env* '("a=b")))
+    (get-lines (open-process "/usr/bin/env" "r")))
+  ("a=b")
+  (let ((*child-env* nil))
+    (get-lines (open-process "/usr/bin/env" "r")))
+  nil)
+
+(test
+  (fcmd
+    (let ((*child-env* '("a=b")))
+      (run "/usr/bin/env")))
+  "a=b\n")