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 tarball for details.
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)
29 static const struct suffix_mult tail_suffixes[] = {
39 #define G (*(struct globals*)&bb_common_bufsiz1)
41 static void tail_xprint_header(const char *fmt, const char *filename)
43 if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
44 bb_perror_nomsg_and_die();
47 static ssize_t tail_read(int fd, char *buf, size_t count)
53 /* /proc files report zero st_size, don't lseek them. */
54 if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
55 current = lseek(fd, 0, SEEK_CUR);
56 if (sbuf.st_size < current)
57 xlseek(fd, 0, SEEK_SET);
60 r = full_read(fd, buf, count);
62 bb_perror_msg(bb_msg_read_error);
63 G.status = EXIT_FAILURE;
69 static const char header_fmt[] ALIGN1 = "\n==> %s <==\n";
71 static unsigned eat_num(const char *p)
77 G.status = 1; /* mark that we saw "+" */
79 return xatou_sfx(p, tail_suffixes);
82 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
83 int tail_main(int argc, char **argv)
86 unsigned sleep_period = 1;
88 const char *str_c, *str_n;
92 unsigned header_threshhold = 1;
99 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
100 /* Allow legacy syntax of an initial numeric option without -n. */
101 if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
102 && isdigit(argv[1][1])
104 count = eat_num(argv[1]);
110 /* -s NUM, -F imlies -f */
111 IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
112 opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
113 &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
114 #define FOLLOW (opt & 0x1)
115 #define COUNT_BYTES (opt & 0x2)
116 //if (opt & 0x1) // -f
117 if (opt & 0x2) count = eat_num(str_c); // -c
118 if (opt & 0x4) count = eat_num(str_n); // -n
119 #if ENABLE_FEATURE_FANCY_TAIL
120 /* q: make it impossible for nfiles to be > header_threshhold */
121 if (opt & 0x8) header_threshhold = UINT_MAX; // -q
122 //if (opt & 0x10) // -s
123 if (opt & 0x20) header_threshhold = 0; // -v
124 # define FOLLOW_RETRY (opt & 0x40)
126 # define FOLLOW_RETRY 0
130 from_top = G.status; /* 1 if there was "-c +N" or "-n +N" */
131 G.status = EXIT_SUCCESS;
133 /* open all the files */
134 fds = xmalloc(sizeof(fds[0]) * (argc + 1));
138 if (fstat(STDIN_FILENO, &statbuf) == 0
139 && S_ISFIFO(statbuf.st_mode)
141 opt &= ~1; /* clear FOLLOW */
143 argv[0] = (char *) bb_msg_standard_input;
147 int fd = open_or_warn_stdin(argv[i]);
148 if (fd < 0 && !FOLLOW_RETRY) {
149 G.status = EXIT_FAILURE;
153 argv[nfiles++] = argv[i];
154 } while (++i < argc);
157 bb_error_msg_and_die("no files");
159 /* prepare the buffer */
160 tailbufsize = BUFSIZ;
161 if (!from_top && COUNT_BYTES) {
162 if (tailbufsize < count + BUFSIZ) {
163 tailbufsize = count + BUFSIZ;
166 tailbuf = xmalloc(tailbufsize);
169 fmt = header_fmt + 1; /* skip header leading newline on first output */
179 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
180 continue; /* may happen with -E */
182 if (nfiles > header_threshhold) {
183 tail_xprint_header(fmt, argv[i]);
188 off_t current = lseek(fd, 0, SEEK_END);
192 /* Optimizing count-bytes case if the file is seekable.
193 * Beware of backing up too far.
194 * Also we exclude files with size 0 (because of /proc/xxx) */
196 continue; /* showing zero bytes is easy :) */
200 xlseek(fd, current, SEEK_SET);
201 bb_copyfd_size(fd, STDOUT_FILENO, count);
204 #if 1 /* This is technically incorrect for *LONG* strings, but very useful */
205 /* Optimizing count-lines case if the file is seekable.
206 * We assume the lines are <64k.
207 * (Users complain that tail takes too long
208 * on multi-gigabyte files) */
209 off = (count | 0xf); /* for small counts, be more paranoid */
210 if (off > (INT_MAX / (64*1024)))
211 off = (INT_MAX / (64*1024));
212 current -= off * (64*1024);
215 xlseek(fd, current, SEEK_SET);
222 /* "We saw 1st line/byte".
223 * Used only by +N code ("start from Nth", 1-based): */
226 while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
230 /* We need to skip a few more bytes/lines */
232 nwrite -= (count - seen);
238 if (*s++ == '\n' && ++seen == count) {
244 xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
248 if (taillen > (int)count) {
249 memmove(tailbuf, tailbuf + taillen - count, count);
254 int newlines_in_buf = 0;
256 do { /* count '\n' in last read */
258 if (buf[k] == '\n') {
263 if (newlines_seen + newlines_in_buf < (int)count) {
264 newlines_seen += newlines_in_buf;
267 int extra = (buf[nread-1] != '\n');
270 k = newlines_seen + newlines_in_buf + extra - count;
278 taillen += nread - (s - tailbuf);
279 memmove(tailbuf, s, taillen);
280 newlines_seen = count - extra;
282 if (tailbufsize < (size_t)taillen + BUFSIZ) {
283 tailbufsize = taillen + BUFSIZ;
284 tailbuf = xrealloc(tailbuf, tailbufsize);
287 buf = tailbuf + taillen;
289 } /* while (tail_read() > 0) */
291 xwrite(STDOUT_FILENO, tailbuf, taillen);
293 } while (++i < nfiles);
295 tailbuf = xrealloc(tailbuf, BUFSIZ);
299 if (FOLLOW) while (1) {
305 const char *filename = argv[i];
309 struct stat sbuf, fsbuf;
312 || fstat(fd, &fsbuf) < 0
313 || stat(filename, &sbuf) < 0
314 || fsbuf.st_dev != sbuf.st_dev
315 || fsbuf.st_ino != sbuf.st_ino
321 new_fd = open(filename, O_RDONLY);
323 bb_error_msg("%s has %s; following end of new file",
324 filename, (fd < 0) ? "appeared" : "been replaced"
326 } else if (fd >= 0) {
327 bb_perror_msg("%s has become inaccessible", filename);
329 fds[i] = fd = new_fd;
332 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
334 if (nfiles > header_threshhold) {
337 while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
339 tail_xprint_header(fmt, filename);
342 xwrite(STDOUT_FILENO, tailbuf, nread);
344 } while (++i < nfiles);
346 if (ENABLE_FEATURE_CLEAN_UP) {