tail(1): Add some long options

Add --blocks, --bytes, and --lines long options for -b, -c, and -n
respectively. This improves tail(1)'s compatibility with its GNU counterpart
in a straightforward way.

Reviewed by:	eadler (earlier version)
MFC after:	3 days

usr.bin/tail/tail.1

@@ -31,7 +31,7 @@
 .\"	@(#)tail.1	8.1 (Berkeley) 6/6/93
 .\" $FreeBSD$
 .\"
-.Dd March 16, 2013
+.Dd April 10, 2018
 .Dt TAIL 1
 .Os
 .Sh NAME
@@ -73,11 +73,11 @@ or the last 10 lines of the input.
 .Pp
 The options are as follows:
 .Bl -tag -width indent
-.It Fl b Ar number
+.It Fl b Ar number , Fl -blocks Ns = Ns Ar number
 The location is
 .Ar number
 512-byte blocks.
-.It Fl c Ar number
+.It Fl c Ar number , Fl -bytes Ns = Ns Ar number
 The location is
 .Ar number
 bytes.
@@ -112,7 +112,7 @@ The
 option is the same as the
 .Fl f
 option if reading from standard input rather than a file.
-.It Fl n Ar number
+.It Fl n Ar number, Fl -lines Ns = Ns Ar number
 The location is
 .Ar number
 lines.

usr.bin/tail/tail.c

@@ -51,6 +51,7 @@ static const char sccsid[] = "@(#)tail.c	8.1 (Berkeley) 6/6/93";
 
 #include <err.h>
 #include <errno.h>
+#include <getopt.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -65,6 +66,14 @@ static file_info_t *files;
 static void obsolete(char **);
 static void usage(void);
 
+static const struct option long_opts[] =
+{
+	{"blocks",	required_argument,	NULL, 'b'},
+	{"bytes",	required_argument,	NULL, 'c'},
+	{"lines",	required_argument,	NULL, 'n'},
+	{NULL,		no_argument,		NULL, 0}
+};
+
 int
 main(int argc, char *argv[])
 {
@@ -113,7 +122,8 @@ main(int argc, char *argv[])
 	obsolete(argv);
 	style = NOTSET;
 	off = 0;
-	while ((ch = getopt(argc, argv, "Fb:c:fn:qr")) != -1)
+	while ((ch = getopt_long(argc, argv, "+Fb:c:fn:qr", long_opts, NULL)) !=
+	    -1)
 		switch(ch) {
 		case 'F':	/* -F is superset of (and implies) -f */
 			Fflag = fflag = 1;