I suppose, it is not a new topic for a discussion, anyway,
here is the diff.

--- arp.c.orig Sun Mar 13 15:54:38 2005
+++ arp.c Fri Mar 25 02:23:44 2005
@@ -103,6 +103,7 @@ extern int h_errno;
#define F_SET 2
#define F_FILESET 3
#define F_DELETE 4
+#define F_REPLACE 5

int
main(int argc, char *argv[])
@@ -113,7 +114,7 @@ main(int argc, char *argv[])
opterr = 0;
func = 0;

- while ((ch = getopt(argc, argv, "andsf")) != -1) {
+ while ((ch = getopt(argc, argv, "andSsf")) != -1) {
switch ((char)ch) {
case 'a':
aflag = 1;
@@ -126,6 +127,11 @@ main(int argc, char *argv[])
usage();
func = F_DELETE;
break;
+ case 'S':
+ if (func)
+ usage();
+ func = F_REPLACE;
+ break;
case 's':
if (func)
usage();
@@ -158,8 +164,12 @@ main(int argc, char *argv[])
usage();
break;
case F_SET:
+ /* FALLTHROUGH */
+ case F_REPLACE:
if (argc < 2 || argc > 5)
usage();
+ if (func == F_REPLACE)
+ (void)delete(argv[0], NULL);
rtn = set(argc, argv) ? 1 : 0;
break;
case F_DELETE:
@@ -205,6 +215,7 @@ file(char *name)
retval = 1;
continue;
}
+ (void)delete(arg[0], NULL);
if (set(i, args))
retval = 1;
}
@@ -528,6 +539,8 @@ usage(void)
(void)fprintf(stderr, "usage: arp -d -a\n");
(void)fprintf(stderr,
"usage: arp -s hostname ether_addr [temp | permanent] [pub]\n");
+ (void)fprintf(stderr,
+ "usage: arp -S hostname ether_addr [temp | permanent] [pub]\n");
(void)fprintf(stderr, "usage: arp -f filename\n");
exit(1);
}
--- arp.8.orig Sat Jul 10 21:30:31 2004
+++ arp.8 Fri Mar 25 02:30:04 2005
@@ -52,6 +52,10 @@
.Op Cm temp | permanent
.Op Cm pub
.Nm arp
+.Fl S Ar hostname ether_addr
+.Op Cm temp | permanent
+.Op Cm pub
+.Nm arp
.Fl f Ar filename
.Sh DESCRIPTION
The
@@ -133,6 +137,13 @@
.Ar ether_addr .
The Ethernet address is given as six hexadecimal bytes separated by
colons.
+.It Fl S Ar hostname ether_addr
+Create or replace an
+.Tn ARP
+entry for the host called
+.Ar hostname
+with the Ethernet address
+.Ar ether_addr .
.Pp
The
.Cm permanent , pub ,