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 //kbuild:lib-$(CONFIG_TAIL) += tail.o
29 //usage:#define tail_trivial_usage
30 //usage: "[OPTIONS] [FILE]..."
31 //usage:#define tail_full_usage "\n\n"
32 //usage: "Print last 10 lines of each FILE (or stdin) to stdout.\n"
33 //usage: "With more than one FILE, precede each with a filename header.\n"
34 //usage: "\n -f Print data as file grows"
35 //usage: IF_FEATURE_FANCY_TAIL(
36 //usage: "\n -s SECONDS Wait SECONDS between reads with -f"
38 //usage: "\n -n N[kbm] Print last N lines"
39 //usage: "\n -n +N[kbm] Start on Nth line and print the rest"
40 //usage: IF_FEATURE_FANCY_TAIL(
41 //usage: "\n -c [+]N[kbm] Print last N bytes"
42 //usage: "\n -q Never print headers"
43 //usage: "\n -v Always print headers"
45 //usage: "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
48 //usage:#define tail_example_usage
49 //usage: "$ tail -n 1 /etc/resolv.conf\n"
50 //usage: "nameserver 10.0.0.1\n"
58 #define G (*(struct globals*)&bb_common_bufsiz1)
59 #define INIT_G() do { } while (0)
61 static void tail_xprint_header(const char *fmt, const char *filename)
63 if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
64 bb_perror_nomsg_and_die();
67 static ssize_t tail_read(int fd, char *buf, size_t count)
71 r = full_read(fd, buf, count);
73 bb_perror_msg(bb_msg_read_error);
74 G.exitcode = EXIT_FAILURE;
80 #define header_fmt_str "\n==> %s <==\n"
82 static unsigned eat_num(const char *p)
90 return xatou_sfx(p, bkm_suffixes);
93 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
94 int tail_main(int argc, char **argv)
97 unsigned sleep_period = 1;
98 const char *str_c, *str_n;
102 unsigned header_threshhold = 1;
111 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
112 /* Allow legacy syntax of an initial numeric option without -n. */
113 if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
114 && isdigit(argv[1][1])
116 count = eat_num(argv[1]);
122 /* -s NUM, -F imlies -f */
123 IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
124 opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
125 &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
126 #define FOLLOW (opt & 0x1)
127 #define COUNT_BYTES (opt & 0x2)
128 //if (opt & 0x1) // -f
129 if (opt & 0x2) count = eat_num(str_c); // -c
130 if (opt & 0x4) count = eat_num(str_n); // -n
131 #if ENABLE_FEATURE_FANCY_TAIL
132 /* q: make it impossible for nfiles to be > header_threshhold */
133 if (opt & 0x8) header_threshhold = UINT_MAX; // -q
134 //if (opt & 0x10) // -s
135 if (opt & 0x20) header_threshhold = 0; // -v
136 # define FOLLOW_RETRY (opt & 0x40)
138 # define FOLLOW_RETRY 0
143 /* open all the files */
144 fds = xmalloc(sizeof(fds[0]) * (argc + 1));
148 if (fstat(STDIN_FILENO, &statbuf) == 0
149 && S_ISFIFO(statbuf.st_mode)
151 opt &= ~1; /* clear FOLLOW */
153 argv[0] = (char *) bb_msg_standard_input;
157 int fd = open_or_warn_stdin(argv[i]);
158 if (fd < 0 && !FOLLOW_RETRY) {
159 G.exitcode = EXIT_FAILURE;
163 argv[nfiles++] = argv[i];
164 } while (++i < argc);
167 bb_error_msg_and_die("no files");
169 /* prepare the buffer */
170 tailbufsize = BUFSIZ;
171 if (!G.from_top && COUNT_BYTES) {
172 if (tailbufsize < count + BUFSIZ) {
173 tailbufsize = count + BUFSIZ;
176 /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
177 * (In fact, it doesn't need ANY memory). So delay allocation.
183 fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
193 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
194 continue; /* may happen with -F */
196 if (nfiles > header_threshhold) {
197 tail_xprint_header(fmt, argv[i]);
198 fmt = header_fmt_str;
202 off_t current = lseek(fd, 0, SEEK_END);
206 /* Optimizing count-bytes case if the file is seekable.
207 * Beware of backing up too far.
208 * Also we exclude files with size 0 (because of /proc/xxx) */
210 continue; /* showing zero bytes is easy :) */
214 xlseek(fd, current, SEEK_SET);
215 bb_copyfd_size(fd, STDOUT_FILENO, count);
218 #if 1 /* This is technically incorrect for *LONG* strings, but very useful */
219 /* Optimizing count-lines case if the file is seekable.
220 * We assume the lines are <64k.
221 * (Users complain that tail takes too long
222 * on multi-gigabyte files) */
223 off = (count | 0xf); /* for small counts, be more paranoid */
224 if (off > (INT_MAX / (64*1024)))
225 off = (INT_MAX / (64*1024));
226 current -= off * (64*1024);
229 xlseek(fd, current, SEEK_SET);
235 tailbuf = xmalloc(tailbufsize);
239 /* "We saw 1st line/byte".
240 * Used only by +N code ("start from Nth", 1-based): */
243 while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
247 /* We need to skip a few more bytes/lines */
249 nwrite -= (count - seen);
255 if (*s++ == '\n' && ++seen == count) {
262 xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
266 if (taillen > (int)count) {
267 memmove(tailbuf, tailbuf + taillen - count, count);
272 int newlines_in_buf = 0;
274 do { /* count '\n' in last read */
276 if (buf[k] == '\n') {
281 if (newlines_seen + newlines_in_buf < (int)count) {
282 newlines_seen += newlines_in_buf;
285 int extra = (buf[nread-1] != '\n');
288 k = newlines_seen + newlines_in_buf + extra - count;
296 taillen += nread - (s - tailbuf);
297 memmove(tailbuf, s, taillen);
298 newlines_seen = count - extra;
300 if (tailbufsize < (size_t)taillen + BUFSIZ) {
301 tailbufsize = taillen + BUFSIZ;
302 tailbuf = xrealloc(tailbuf, tailbufsize);
305 buf = tailbuf + taillen;
307 } /* while (tail_read() > 0) */
309 xwrite(STDOUT_FILENO, tailbuf, taillen);
311 } while (++i < nfiles);
313 tailbuf = xrealloc(tailbuf, BUFSIZ);
317 if (FOLLOW) while (1) {
323 const char *filename = argv[i];
327 struct stat sbuf, fsbuf;
330 || fstat(fd, &fsbuf) < 0
331 || stat(filename, &sbuf) < 0
332 || fsbuf.st_dev != sbuf.st_dev
333 || fsbuf.st_ino != sbuf.st_ino
339 new_fd = open(filename, O_RDONLY);
341 bb_error_msg("%s has %s; following end of new file",
342 filename, (fd < 0) ? "appeared" : "been replaced"
344 } else if (fd >= 0) {
345 bb_perror_msg("%s has become inaccessible", filename);
347 fds[i] = fd = new_fd;
350 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
352 if (nfiles > header_threshhold) {
353 fmt = header_fmt_str;
356 /* tail -f keeps following files even if they are truncated */
358 /* /proc files report zero st_size, don't lseek them */
359 if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
360 off_t current = lseek(fd, 0, SEEK_CUR);
361 if (sbuf.st_size < current)
362 xlseek(fd, 0, SEEK_SET);
365 nread = tail_read(fd, tailbuf, BUFSIZ);
369 tail_xprint_header(fmt, filename);
372 xwrite(STDOUT_FILENO, tailbuf, nread);
374 } while (++i < nfiles);
377 if (ENABLE_FEATURE_CLEAN_UP) {