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

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Date:   Wed, 15 Aug 2018 08:40:20 -0600
From:   David Ahern <dsahern@...il.com>
To:     Phil Sutter <phil@....cc>,
        Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org, Till Maas <opensource@...l.name>
Subject: Re: [iproute PATCH 4/4] lib: Enable colored output only for TTYs

On 8/15/18 3:06 AM, Phil Sutter wrote:
> 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.
> 
> Signed-off-by: Phil Sutter <phil@....cc>
> ---
>  lib/color.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/color.c b/lib/color.c
> index edf96e5c6ecd7..500ba09682697 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 +80,7 @@ void enable_color(void)
>  
>  int check_enable_color(int color, int json)
>  {
> -	if (color && !json) {
> +	if (color && !json && isatty(fileno(stdout))) {
>  		enable_color();
>  		return 0;
>  	}
> 

This also disables color sequence when the output is piped to a pager
such as less which with the -R argument can handle it just fine.

ie., the user needs to remove the color arg when that output is not wanted.