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, 3 insertions, 0 deletions

diff --git a/sysif.h b/sysif.h
index 6dc150e2..2da92a32 100644
--- a/sysif.h
+++ b/sysif.h
@@ -36,6 +36,9 @@ extern val atime_s, mtime_s, ctime_s;
 extern val atime_nsec_s, mtime_nsec_s, ctime_nsec_s;
 extern val path_s;
 
+extern val child_env_s;
+#define child_env (deref(lookup_var_l(nil, child_env_s)))
+
 val errno_to_file_error(int err);
 val env(void);
 val replace_env(val env_list);