ls(1): Support other aliases for --color arguments used by GNU ls(1)

These aliases are supported and documented in the man page. For now, they
will not be mentioned in the error when an invalid argument is encountered,
instead keeping that list to the shorter 'preferred' names of each argument.

Reported by:	rgrimes

bin/ls/ls.1

@@ -32,7 +32,7 @@
 .\"     @(#)ls.1	8.7 (Berkeley) 7/29/94
 .\" $FreeBSD$
 .\"
-.Dd August 16, 2018
+.Dd August 18, 2018
 .Dt LS 1
 .Os
 .Sh NAME
@@ -252,6 +252,26 @@ environment variable is set and not empty.
 .Pp
 .Cm never
 will disable color regardless of environment variables.
+.Pp
+For compatibility with GNU coreutils,
+.Nm
+supports
+.Cm yes
+or
+.Cm force
+as equivalent to
+.Cm always ,
+.Cm no
+or
+.Cm none
+as equivalent to
+.Cm never ,
+and
+.Cm tty
+or
+.Cm if-tty
+as equivalent to
+.Cm auto .
 .It Fl d
 Directories are listed as plain files (not searched recursively).
 .It Fl f

bin/ls/ls.c

@@ -200,6 +200,30 @@ do_color(void)
 	return (do_color_from_env());
 }
 
+static bool
+do_color_always(const char *term)
+{
+
+	return (strcmp(term, "always") == 0 || strcmp(term, "yes") == 0 ||
+	    strcmp(term, "force") == 0);
+}
+
+static bool
+do_color_never(const char *term)
+{
+
+	return (strcmp(term, "never") == 0 || strcmp(term, "no") == 0 ||
+	    strcmp(term, "none") == 0);
+}
+
+static bool
+do_color_auto(const char *term)
+{
+
+	return (strcmp(term, "auto") == 0 || strcmp(term, "tty") == 0 ||
+	    strcmp(term, "if-tty") == 0);
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -406,11 +430,11 @@ main(int argc, char *argv[])
 			break;
 #ifdef COLORLS
 		case COLOR_OPT:
-			if (optarg == NULL || strcmp(optarg, "always") == 0)
+			if (optarg == NULL || do_color_always(optarg))
 				colorflag = COLORFLAG_ALWAYS;
-			else if (strcmp(optarg, "auto") == 0)
+			else if (do_color_auto(optarg))
 				colorflag = COLORFLAG_AUTO;
-			else if (strcmp(optarg, "never") == 0)
+			else if (do_color_never(optarg))
 				colorflag = COLORFLAG_NEVER;
 			else
 				errx(2, "unsupported --color value '%s' (must be always, auto, or never)",