open-process: I/O redirection feature.

In the mode-string of open-process, I/O redirections can now
be specified that are carried out in the child process.

* stream.c (do_parse_mode): Parse the redirection syntax
indicated by >, which has a short and long form.
The redirections are entered into a small table in the mode
structure.
(open_process): In the child process, perform the redirection
specified in the mode structure's redirection table.

* stream.h (STDIO_MODE_NREDIRS): New preprprocessor symbol.
(struct stdio_mode): New array member, redir.

* txr.1: Documented.

1 files changed, 3 insertions, 0 deletions

diff --git a/stream.h b/stream.h
index 9bae897c..5d137d47 100644
--- a/stream.h
+++ b/stream.h
@@ -99,6 +99,8 @@ struct strm_ops {
     get_error, get_error_str, clear_error, get_fd, 0, 0, 0, 0                \
 }
 
+#define STDIO_MODE_NREDIRS 4
+
 struct stdio_mode {
   unsigned malformed : 1;
   unsigned read : 1;
@@ -110,6 +112,7 @@ struct stdio_mode {
   unsigned unbuf : 1;
   unsigned linebuf : 1;
   int buforder : 5;
+  int redir[STDIO_MODE_NREDIRS][2];
 };
 
 #define stdio_mode_init_blank { 0, 0, 0, 0, 0, 0, 0, 0, 0, -1 }