diff: add support for --help and --version

Add support for --help and --version to be compatible with gnu diff.

gnu diff --help writes to stdout, do the same to be compatible

Reviewed by:	bapt, pstef, debrup, Pau Amma
Sponsored by:	Klara Inc.
Differential Revision:	https://reviews.freebsd.org/D34508

2 files changed, 35 insertions, 5 deletions

diff --git a/usr.bin/diff/diff.1 b/usr.bin/diff/diff.1
index b17ddb123fd5..8582db6c9c1c 100644
--- a/usr.bin/diff/diff.1
+++ b/usr.bin/diff/diff.1
@@ -30,7 +30,7 @@
 .\"     @(#)diff.1	8.1 (Berkeley) 6/30/93
 .\" $FreeBSD$
 .\"
-.Dd June 19, 2020
+.Dd March 10, 2022
 .Dt DIFF 1
 .Os
 .Sh NAME
@@ -207,6 +207,9 @@
 .Op Fl -width
 .Fl y | Fl -side-by-side
 .Ar file1 file2
+.Nm diff
+.Op Fl -help
+.Op Fl -version
 .Sh DESCRIPTION
 The
 .Nm
@@ -282,6 +285,8 @@ Identical output to that of the
 flag, but in reverse order.
 It cannot be digested by
 .Xr ed 1 .
+.It Fl -help
+This option prints a summary to stdout and exits with status 0.
 .It Fl n
 Produces a script similar to that of
 .Fl e ,
@@ -308,6 +313,8 @@ However, unlike with
 .Fl c ,
 all lines to be changed (added and/or removed) are present in
 a single section.
+.It Fl -version
+This option prints a version string to stdout and exits with status 0.
 .It Fl y Fl -side-by-side
 Output in two columns with a marker between them.
 The marker can be one
@@ -655,6 +662,12 @@ Differences were found.
 .It >1
 An error occurred.
 .El
+.Pp
+The
+.Fl -help
+and
+.Fl -version
+options exit with a status of 0.
 .Sh EXAMPLES
 Compare
 .Pa old_dir
diff --git a/usr.bin/diff/diff.c b/usr.bin/diff/diff.c
index 34cdd0d846d9..ba6bc7c3a310 100644
--- a/usr.bin/diff/diff.c
+++ b/usr.bin/diff/diff.c
@@ -38,8 +38,10 @@ __FBSDID("$FreeBSD$");
 #include "diff.h"
 #include "xmalloc.h"
 
+static const char diff_version[] = "FreeBSD diff 20220309";
 bool	 lflag, Nflag, Pflag, rflag, sflag, Tflag, cflag;
 bool	 ignore_file_case, suppress_common, color, noderef;
+static bool help = false;
 int	 diff_format, diff_context, status;
 int	 tabsize = 8, width = 130;
 static int	colorflag = COLORFLAG_NEVER;
@@ -58,11 +60,13 @@ enum {
 	OPT_IGN_FN_CASE,
 	OPT_NO_IGN_FN_CASE,
 	OPT_NORMAL,
+	OPT_HELP,
 	OPT_HORIZON_LINES,
 	OPT_CHANGED_GROUP_FORMAT,
 	OPT_SUPPRESS_COMMON,
 	OPT_COLOR,
 	OPT_NO_DEREFERENCE,
+	OPT_VERSION,
 };
 
 static struct option longopts[] = {
@@ -97,6 +101,7 @@ static struct option longopts[] = {
 	{ "exclude-from",		required_argument,	0,	'X' },
 	{ "side-by-side",		no_argument,		NULL,	'y' },
 	{ "ignore-file-name-case",	no_argument,		NULL,	OPT_IGN_FN_CASE },
+	{ "help",			no_argument,		NULL,	OPT_HELP},
 	{ "horizon-lines",		required_argument,	NULL,	OPT_HORIZON_LINES },
 	{ "no-dereference",		no_argument,		NULL,	OPT_NO_DEREFERENCE},
 	{ "no-ignore-file-name-case",	no_argument,		NULL,	OPT_NO_IGN_FN_CASE },
@@ -106,6 +111,7 @@ static struct option longopts[] = {
 	{ "changed-group-format",	required_argument,	NULL,	OPT_CHANGED_GROUP_FORMAT},
 	{ "suppress-common-lines",	no_argument,		NULL,	OPT_SUPPRESS_COMMON },
 	{ "color",			optional_argument,	NULL,	OPT_COLOR },
+	{ "version",			no_argument,		NULL,	OPT_VERSION},
 	{ NULL,				0,			0,	'\0'}
 };
 
@@ -294,6 +300,10 @@ main(int argc, char **argv)
 			diff_format = D_GFORMAT;
 			group_format = optarg;
 			break;
+		case OPT_HELP:
+			help = true;
+			usage();
+			break;
 		case OPT_HORIZON_LINES:
 			break; /* XXX TODO for compatibility with GNU diff3 */
 		case OPT_IGN_FN_CASE:
@@ -335,6 +345,9 @@ main(int argc, char **argv)
 			rflag = true;
 			noderef = true;
 			break;
+		case OPT_VERSION:
+			printf("%s\n", diff_version);
+			exit(0);
 		default:
 			usage();
 			break;
@@ -569,9 +582,9 @@ print_status(int val, char *path1, char *path2, const char *entry)
 }
 
 static void
-usage(void)
+usage()
 {
-	(void)fprintf(stderr,
+	(void)fprintf(help ? stdout : stderr,
 	    "usage: diff [-aBbdilpTtw] [-c | -e | -f | -n | -q | -u] [--ignore-case]\n"
 	    "            [--no-ignore-case] [--normal] [--strip-trailing-cr] [--tabsize]\n"
 	    "            [-I pattern] [-F pattern] [-L label] file1 file2\n"
@@ -590,9 +603,13 @@ usage(void)
 	    "            [--ignore-blank-lines] [--ignore-case] [--minimal]\n"
 	    "            [--no-ignore-file-name-case] [--strip-trailing-cr]\n"
 	    "            [--suppress-common-lines] [--tabsize] [--text] [--width]\n"
-	    "            -y | --side-by-side file1 file2\n");
+	    "            -y | --side-by-side file1 file2\n"
+	    "       diff [--help] [--version]\n");
 
-	exit(2);
+	if (help)
+		exit(0);
+	else
+		exit(2);
 }
 
 static void