[git commit] libbb: send usage messages to correct stream

[Denys Vlasenko]

commit: https://git.busybox.net/busybox/commit/?id=dbd14c4a42454b61a5474f6243865a6ec113e60b
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master

POSIX generally requires normal output to go to stdout and
diagnostic (i.e. error) output to go to stderr.

When usage messages for BusyBox applets are specifically requested
by the user (e.g. 'find --help') they should go to stdout; when
they're emitted due to an error they should go to stderr.

function                                             old     new   delta
bb_show_usage                                        148     146      -2
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-2)               Total: -2 bytes

Signed-off-by: Avi Halachmi <avihpit at yahoo.com>
Signed-off-by: Ron Yorston <rmy at pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 libbb/appletlib.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index ad373ae1c..d2e5900b5 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -127,17 +127,19 @@ static const char packed_usage[] ALIGN1 = { PACKED_USAGE };
 void FAST_FUNC bb_show_usage(void)
 {
 	if (ENABLE_SHOW_USAGE) {
+		ssize_t FAST_FUNC (*full_write_fn)(const char *) =
+				xfunc_error_retval ? full_write2_str : full_write1_str;
 #ifdef SINGLE_APPLET_STR
 		/* Imagine that this applet is "true". Dont link in printf! */
 		const char *usage_string = unpack_usage_messages();
 
 		if (usage_string) {
 			if (*usage_string == '\b') {
-				full_write2_str("No help available\n");
+				full_write_fn("No help available\n");
 			} else {
-				full_write2_str("Usage: "SINGLE_APPLET_STR" ");
-				full_write2_str(usage_string);
-				full_write2_str("\n");
+				full_write_fn("Usage: "SINGLE_APPLET_STR" ");
+				full_write_fn(usage_string);
+				full_write_fn("\n");
 			}
 			if (ENABLE_FEATURE_CLEAN_UP)
 				dealloc_usage_messages((char*)usage_string);
@@ -153,19 +155,19 @@ void FAST_FUNC bb_show_usage(void)
 			while (*p++) continue;
 			ap--;
 		}
-		full_write2_str(bb_banner);
-		full_write2_str(" multi-call binary.\n"); /* common string */
+		full_write_fn(bb_banner);
+		full_write_fn(" multi-call binary.\n"); /* common string */
 		if (*p == '\b')
-			full_write2_str("\nNo help available\n");
+			full_write_fn("\nNo help available\n");
 		else {
-			full_write2_str("\nUsage: ");
-			full_write2_str(applet_name);
+			full_write_fn("\nUsage: ");
+			full_write_fn(applet_name);
 			if (p[0]) {
 				if (p[0] != '\n')
-					full_write2_str(" ");
-				full_write2_str(p);
+					full_write_fn(" ");
+				full_write_fn(p);
 			}
-			full_write2_str("\n");
+			full_write_fn("\n");
 		}
 		if (ENABLE_FEATURE_CLEAN_UP)
 			dealloc_usage_messages((char*)usage_string);
@@ -268,8 +270,10 @@ void lbb_prepare(const char *applet
 		 && !(ENABLE_TRUE && strcmp(applet_name, "true") == 0)
 		 && !(ENABLE_FALSE && strcmp(applet_name, "false") == 0)
 		 && !(ENABLE_ECHO && strcmp(applet_name, "echo") == 0)
-		)
+		) {
+			xfunc_error_retval = 0;
 			bb_show_usage();
+		}
 	}
 #endif
 }