netdev - [iproute PATCH v2 4/4] lib: Enable colored output only for TTYs

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Date:   Wed, 15 Aug 2018 18:21:27 +0200
From:   Phil Sutter <phil@....cc>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org, Till Maas <opensource@...l.name>,
        David Ahern <dsahern@...il.com>
Subject: [iproute PATCH v2 4/4] lib: Enable colored output only for TTYs

Add an additional prerequisite to check_enable_color() to make sure
stdout actually points to an open TTY device. Otherwise calls like

| ip -color a s >/tmp/foo

will print color escape sequences into that file. Allow to override this
check by specifying '-color' flag more than once.

Signed-off-by: Phil Sutter <phil@....cc>
---
Changes since v1:
- Allow to override isatty() check by specifying '-color' flag more than
  once.
- Document new behaviour in man pages.
---
 lib/color.c       | 6 +++++-
 man/man8/bridge.8 | 5 ++++-
 man/man8/ip.8     | 5 ++++-
 man/man8/tc.8     | 5 ++++-
 4 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/lib/color.c b/lib/color.c
index edf96e5c6ecd7..3a66d8ccb4b00 100644
--- a/lib/color.c
+++ b/lib/color.c
@@ -3,6 +3,7 @@
 #include <stdarg.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <linux/if.h>
@@ -79,7 +80,10 @@ void enable_color(void)
 
 int check_enable_color(int color, int json)
 {
-	if (color && !json) {
+	if (json || !color)
+		return 1;
+
+	if (color > 1 || isatty(fileno(stdout))) {
 		enable_color();
 		return 0;
 	}
diff --git a/man/man8/bridge.8 b/man/man8/bridge.8
index e7f7148315e19..b865e8b6cd771 100644
--- a/man/man8/bridge.8
+++ b/man/man8/bridge.8
@@ -171,7 +171,10 @@ return code will be non zero.
 
 .TP
 .BR "\-c" , " -color"
-Use color output.
+Use color output if stdout is a terminal. Specify twice to enable color output
+irrespective of stdout state. This flag is ignored if
+.B \-json
+is also given.
 
 .TP
 .BR "\-j", " \-json"
diff --git a/man/man8/ip.8 b/man/man8/ip.8
index 0087d18b74706..c5484bbc11483 100644
--- a/man/man8/ip.8
+++ b/man/man8/ip.8
@@ -188,7 +188,10 @@ executes specified command over all objects, it depends if command supports this
 
 .TP
 .BR "\-c" , " -color"
-Use color output.
+Use color output if stdout is a terminal. Specify twice to enable color output
+irrespective of stdout state. This flag is ignored if
+.B \-json
+is also given.
 
 .TP
 .BR "\-t" , " \-timestamp"
diff --git a/man/man8/tc.8 b/man/man8/tc.8
index 840880fbdba63..cbe7ac1847bbb 100644
--- a/man/man8/tc.8
+++ b/man/man8/tc.8
@@ -730,7 +730,10 @@ option.
 
 .TP
 .BR "\ -color"
-Use color output.
+Use color output if stdout is a terminal. Specify twice to enable color output
+irrespective of stdout state. This flag is ignored if
+.B \-json
+is also given.
 
 .TP
 .BR "\-j", " \-json"
-- 
2.18.0