run-command: Allow stderr to be a caller supplied pipe

spearce · gitster · commit 4f41b611481b · 2010-02-05T20:57:16.000-08:00
Like .out, .err may now be set to a file descriptor &gt; 0, which
is a writable pipe/socket/file that the child's stderr will be
redirected into.

Signed-off-by: Shawn O. Pearce &lt;spearce@spearce.org&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/Documentation/technical/api-run-command.txt b/Documentation/technical/api-run-command.txt
@@ -135,7 +135,7 @@ stderr as follows:
 
 	.in: The FD must be readable; it becomes child's stdin.
 	.out: The FD must be writable; it becomes child's stdout.
-	.err > 0 is not supported.
+	.err: The FD must be writable; it becomes child's stderr.
 
   The specified FD is closed by start_command(), even if it fails to
   run the sub-process!
diff --git a/run-command.c b/run-command.c
@@ -94,6 +94,9 @@ int start_command(struct child_process *cmd)
 		else if (need_err) {
 			dup2(fderr[1], 2);
 			close_pair(fderr);
+		} else if (cmd->err > 1) {
+			dup2(cmd->err, 2);
+			close(cmd->err);
 		}
 
 		if (cmd->no_stdout)
@@ -156,6 +159,9 @@ int start_command(struct child_process *cmd)
 	} else if (need_err) {
 		s2 = dup(2);
 		dup2(fderr[1], 2);
+	} else if (cmd->err > 2) {
+		s2 = dup(2);
+		dup2(cmd->err, 2);
 	}
 
 	if (cmd->no_stdout) {
@@ -228,6 +234,8 @@ int start_command(struct child_process *cmd)
 
 	if (need_err)
 		close(fderr[1]);
+	else if (cmd->err)
+		close(cmd->err);
 
 	return 0;
 }
diff --git a/run-command.h b/run-command.h
@@ -18,7 +18,7 @@ struct child_process {
 	 * - Specify > 0 to set a channel to a particular FD as follows:
 	 *     .in: a readable FD, becomes child's stdin
 	 *     .out: a writable FD, becomes child's stdout/stderr
-	 *     .err > 0 not supported
+	 *     .err: a writable FD, becomes child's stderr
 	 *   The specified FD is closed by start_command(), even in case
 	 *   of errors!
 	 */
