1 /* vi: set sw=4 ts=4: */
3 * Mini tail implementation for busybox
5 * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
7 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
10 /* BB_AUDIT SUSv3 compliant (need fancy for -c) */
11 /* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
12 /* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
14 /* Mar 16, 2003 Manuel Novoa III (mjn3@codepoet.org)
16 * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
17 * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
18 * 1) mixing printf/write without fflush()ing stdout
19 * 2) no check that any open files are present
20 * 3) optstring had -q taking an arg
21 * 4) no error checking on write in some cases, and a warning even then
22 * 5) q and s interaction bug
23 * 6) no check for lseek error
24 * 7) lseek attempted when count==0 even if arg was +0 (from top)
27 //usage:#define tail_trivial_usage
28 //usage: "[OPTIONS] [FILE]..."
29 //usage:#define tail_full_usage "\n\n"
30 //usage: "Print last 10 lines of each FILE (or stdin) to stdout.\n"
31 //usage: "With more than one FILE, precede each with a filename header.\n"
32 //usage: "\n -f Print data as file grows"
33 //usage: IF_FEATURE_FANCY_TAIL(
34 //usage: "\n -s SECONDS Wait SECONDS between reads with -f"
36 //usage: "\n -n N[kbm] Print last N lines"
37 //usage: IF_FEATURE_FANCY_TAIL(
38 //usage: "\n -c N[kbm] Print last N bytes"
39 //usage: "\n -q Never print headers"
40 //usage: "\n -v Always print headers"
42 //usage: "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
43 //usage: "\nIf N starts with a '+', output begins with the Nth item from the start"
44 //usage: "\nof each file, not from the end."
47 //usage:#define tail_example_usage
48 //usage: "$ tail -n 1 /etc/resolv.conf\n"
49 //usage: "nameserver 10.0.0.1\n"
53 static const struct suffix_mult tail_suffixes[] = {
64 #define G (*(struct globals*)&bb_common_bufsiz1)
65 #define INIT_G() do { } while (0)
67 static void tail_xprint_header(const char *fmt, const char *filename)
69 if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
70 bb_perror_nomsg_and_die();
73 static ssize_t tail_read(int fd, char *buf, size_t count)
79 /* /proc files report zero st_size, don't lseek them. */
80 if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
81 current = lseek(fd, 0, SEEK_CUR);
82 if (sbuf.st_size < current)
83 xlseek(fd, 0, SEEK_SET);
86 r = full_read(fd, buf, count);
88 bb_perror_msg(bb_msg_read_error);
89 G.exitcode = EXIT_FAILURE;
95 #define header_fmt_str "\n==> %s <==\n"
97 static unsigned eat_num(const char *p)
101 else if (*p == '+') {
105 return xatou_sfx(p, tail_suffixes);
108 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
109 int tail_main(int argc, char **argv)
112 unsigned sleep_period = 1;
113 const char *str_c, *str_n;
117 unsigned header_threshhold = 1;
126 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
127 /* Allow legacy syntax of an initial numeric option without -n. */
128 if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
129 && isdigit(argv[1][1])
131 count = eat_num(argv[1]);
137 /* -s NUM, -F imlies -f */
138 IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
139 opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
140 &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
141 #define FOLLOW (opt & 0x1)
142 #define COUNT_BYTES (opt & 0x2)
143 //if (opt & 0x1) // -f
144 if (opt & 0x2) count = eat_num(str_c); // -c
145 if (opt & 0x4) count = eat_num(str_n); // -n
146 #if ENABLE_FEATURE_FANCY_TAIL
147 /* q: make it impossible for nfiles to be > header_threshhold */
148 if (opt & 0x8) header_threshhold = UINT_MAX; // -q
149 //if (opt & 0x10) // -s
150 if (opt & 0x20) header_threshhold = 0; // -v
151 # define FOLLOW_RETRY (opt & 0x40)
153 # define FOLLOW_RETRY 0
158 /* open all the files */
159 fds = xmalloc(sizeof(fds[0]) * (argc + 1));
163 if (fstat(STDIN_FILENO, &statbuf) == 0
164 && S_ISFIFO(statbuf.st_mode)
166 opt &= ~1; /* clear FOLLOW */
168 argv[0] = (char *) bb_msg_standard_input;
172 int fd = open_or_warn_stdin(argv[i]);
173 if (fd < 0 && !FOLLOW_RETRY) {
174 G.exitcode = EXIT_FAILURE;
178 argv[nfiles++] = argv[i];
179 } while (++i < argc);
182 bb_error_msg_and_die("no files");
184 /* prepare the buffer */
185 tailbufsize = BUFSIZ;
186 if (!G.from_top && COUNT_BYTES) {
187 if (tailbufsize < count + BUFSIZ) {
188 tailbufsize = count + BUFSIZ;
191 /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
192 * (In fact, it doesn't need ANY memory). So delay allocation.
198 fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
208 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
209 continue; /* may happen with -F */
211 if (nfiles > header_threshhold) {
212 tail_xprint_header(fmt, argv[i]);
213 fmt = header_fmt_str;
217 off_t current = lseek(fd, 0, SEEK_END);
221 /* Optimizing count-bytes case if the file is seekable.
222 * Beware of backing up too far.
223 * Also we exclude files with size 0 (because of /proc/xxx) */
225 continue; /* showing zero bytes is easy :) */
229 xlseek(fd, current, SEEK_SET);
230 bb_copyfd_size(fd, STDOUT_FILENO, count);
233 #if 1 /* This is technically incorrect for *LONG* strings, but very useful */
234 /* Optimizing count-lines case if the file is seekable.
235 * We assume the lines are <64k.
236 * (Users complain that tail takes too long
237 * on multi-gigabyte files) */
238 off = (count | 0xf); /* for small counts, be more paranoid */
239 if (off > (INT_MAX / (64*1024)))
240 off = (INT_MAX / (64*1024));
241 current -= off * (64*1024);
244 xlseek(fd, current, SEEK_SET);
250 tailbuf = xmalloc(tailbufsize);
254 /* "We saw 1st line/byte".
255 * Used only by +N code ("start from Nth", 1-based): */
258 while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
262 /* We need to skip a few more bytes/lines */
264 nwrite -= (count - seen);
270 if (*s++ == '\n' && ++seen == count) {
277 xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
281 if (taillen > (int)count) {
282 memmove(tailbuf, tailbuf + taillen - count, count);
287 int newlines_in_buf = 0;
289 do { /* count '\n' in last read */
291 if (buf[k] == '\n') {
296 if (newlines_seen + newlines_in_buf < (int)count) {
297 newlines_seen += newlines_in_buf;
300 int extra = (buf[nread-1] != '\n');
303 k = newlines_seen + newlines_in_buf + extra - count;
311 taillen += nread - (s - tailbuf);
312 memmove(tailbuf, s, taillen);
313 newlines_seen = count - extra;
315 if (tailbufsize < (size_t)taillen + BUFSIZ) {
316 tailbufsize = taillen + BUFSIZ;
317 tailbuf = xrealloc(tailbuf, tailbufsize);
320 buf = tailbuf + taillen;
322 } /* while (tail_read() > 0) */
324 xwrite(STDOUT_FILENO, tailbuf, taillen);
326 } while (++i < nfiles);
328 tailbuf = xrealloc(tailbuf, BUFSIZ);
332 if (FOLLOW) while (1) {
338 const char *filename = argv[i];
342 struct stat sbuf, fsbuf;
345 || fstat(fd, &fsbuf) < 0
346 || stat(filename, &sbuf) < 0
347 || fsbuf.st_dev != sbuf.st_dev
348 || fsbuf.st_ino != sbuf.st_ino
354 new_fd = open(filename, O_RDONLY);
356 bb_error_msg("%s has %s; following end of new file",
357 filename, (fd < 0) ? "appeared" : "been replaced"
359 } else if (fd >= 0) {
360 bb_perror_msg("%s has become inaccessible", filename);
362 fds[i] = fd = new_fd;
365 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
367 if (nfiles > header_threshhold) {
368 fmt = header_fmt_str;
370 while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
372 tail_xprint_header(fmt, filename);
375 xwrite(STDOUT_FILENO, tailbuf, nread);
377 } while (++i < nfiles);
380 if (ENABLE_FEATURE_CLEAN_UP) {