1 /* vi: set sw=4 ts=4: */
2 /*
3 * Mini tail implementation for busybox
4 *
5 * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
6 *
7 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
8 */
9 /* Mar 16, 2003 Manuel Novoa III (mjn3@codepoet.org)
10 *
11 * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
12 * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
13 * 1) mixing printf/write without fflush()ing stdout
14 * 2) no check that any open files are present
15 * 3) optstring had -q taking an arg
16 * 4) no error checking on write in some cases, and a warning even then
17 * 5) q and s interaction bug
18 * 6) no check for lseek error
19 * 7) lseek attempted when count==0 even if arg was +0 (from top)
20 */
21 //config:config TAIL
22 //config: bool "tail (6.8 kb)"
23 //config: default y
24 //config: help
25 //config: tail is used to print the last specified number of lines
26 //config: from files.
27 //config:
28 //config:config FEATURE_FANCY_TAIL
29 //config: bool "Enable -q, -s, -v, and -F options"
30 //config: default y
31 //config: depends on TAIL
32 //config: help
33 //config: These options are provided by GNU tail, but
34 //config: are not specified in the SUSv3 standard:
35 //config: -q Never output headers giving file names
36 //config: -s SEC Wait SEC seconds between reads with -f
37 //config: -v Always output headers giving file names
38 //config: -F Same as -f, but keep retrying
39
40 //applet:IF_TAIL(APPLET(tail, BB_DIR_USR_BIN, BB_SUID_DROP))
41
42 //kbuild:lib-$(CONFIG_TAIL) += tail.o
43
44 /* BB_AUDIT SUSv3 compliant (need fancy for -c) */
45 /* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
46 /* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
47
48 //usage:#define tail_trivial_usage
49 //usage: "[OPTIONS] [FILE]..."
50 //usage:#define tail_full_usage "\n\n"
51 //usage: "Print last 10 lines of FILEs (or stdin) to.\n"
52 //usage: "With more than one FILE, precede each with a filename header.\n"
53 //usage: "\n -c [+]N[bkm] Print last N bytes"
54 //usage: "\n -n N[bkm] Print last N lines"
55 //usage: "\n -n +N[bkm] Start on Nth line and print the rest"
56 //usage: "\n (b:*512 k:*1024 m:*1024^2)"
57 //usage: IF_FEATURE_FANCY_TAIL(
58 //usage: "\n -q Never print headers"
59 //usage: "\n -v Always print headers"
60 //usage: )
61 //usage: "\n -f Print data as file grows"
62 //usage: IF_FEATURE_FANCY_TAIL(
63 //usage: "\n -F Same as -f, but keep retrying"
64 //usage: "\n -s SECONDS Wait SECONDS between reads with -f"
65 //usage: )
66 //usage:
67 //usage:#define tail_example_usage
68 //usage: "$ tail -n 1 /etc/resolv.conf\n"
69 //usage: "nameserver 10.0.0.1\n"
70
71 #include "libbb.h"
72 #include "common_bufsiz.h"
73
74 struct globals {
75 bool from_top;
76 bool exitcode;
77 } FIX_ALIASING;
78 #define G (*(struct globals*)bb_common_bufsiz1)
79 #define INIT_G() do { setup_common_bufsiz(); } while (0)
80
tail_xprint_header(const char * fmt,const char * filename)81 static void tail_xprint_header(const char *fmt, const char *filename)
82 {
83 if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
84 bb_perror_nomsg_and_die();
85 }
86
tail_read(int fd,char * buf,size_t count)87 static ssize_t tail_read(int fd, char *buf, size_t count)
88 {
89 ssize_t r;
90
91 r = full_read(fd, buf, count);
92 if (r < 0) {
93 bb_simple_perror_msg(bb_msg_read_error);
94 G.exitcode = EXIT_FAILURE;
95 }
96
97 return r;
98 }
99
100 #define header_fmt_str "\n==> %s <==\n"
101
eat_num(const char * p)102 static unsigned eat_num(const char *p)
103 {
104 if (*p == '-')
105 p++;
106 else if (*p == '+') {
107 p++;
108 G.from_top = 1;
109 }
110 return xatou_sfx(p, bkm_suffixes);
111 }
112
113 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
tail_main(int argc,char ** argv)114 int tail_main(int argc, char **argv)
115 {
116 unsigned count = 10;
117 unsigned sleep_period = 1;
118 const char *str_c, *str_n;
119
120 char *tailbuf;
121 size_t tailbufsize;
122 unsigned header_threshold = 1;
123 unsigned nfiles;
124 int i, opt;
125
126 int *fds;
127 const char *fmt;
128 int prev_fd;
129
130 INIT_G();
131
132 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
133 /* Allow legacy syntax of an initial numeric option without -n. */
134 if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
135 && isdigit(argv[1][1])
136 ) {
137 count = eat_num(argv[1]);
138 argv++;
139 argc--;
140 }
141 #endif
142
143 /* -s NUM, -F imlies -f */
144 opt = getopt32(argv, IF_FEATURE_FANCY_TAIL("^")
145 "fc:n:"IF_FEATURE_FANCY_TAIL("qs:+vF")
146 IF_FEATURE_FANCY_TAIL("\0" "Ff"),
147 &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period)
148 );
149 #define FOLLOW (opt & 0x1)
150 #define COUNT_BYTES (opt & 0x2)
151 //if (opt & 0x1) // -f
152 if (opt & 0x2) count = eat_num(str_c); // -c
153 if (opt & 0x4) count = eat_num(str_n); // -n
154 #if ENABLE_FEATURE_FANCY_TAIL
155 /* q: make it impossible for nfiles to be > header_threshold */
156 if (opt & 0x8) header_threshold = UINT_MAX; // -q
157 //if (opt & 0x10) // -s
158 if (opt & 0x20) header_threshold = 0; // -v
159 # define FOLLOW_RETRY (opt & 0x40)
160 #else
161 # define FOLLOW_RETRY 0
162 #endif
163 argc -= optind;
164 argv += optind;
165
166 /* open all the files */
167 fds = xmalloc(sizeof(fds[0]) * (argc + 1));
168 if (!argv[0]) {
169 struct stat statbuf;
170
171 if (fstat(STDIN_FILENO, &statbuf) == 0
172 && S_ISFIFO(statbuf.st_mode)
173 ) {
174 opt &= ~1; /* clear FOLLOW */
175 }
176 argv[0] = (char *) bb_msg_standard_input;
177 }
178 nfiles = i = 0;
179 do {
180 int fd = open_or_warn_stdin(argv[i]);
181 if (fd < 0 && !FOLLOW_RETRY) {
182 G.exitcode = EXIT_FAILURE;
183 continue;
184 }
185 fds[nfiles] = fd;
186 argv[nfiles++] = argv[i];
187 } while (++i < argc);
188
189 if (!nfiles)
190 bb_simple_error_msg_and_die("no files");
191
192 /* prepare the buffer */
193 tailbufsize = BUFSIZ;
194 if (!G.from_top && COUNT_BYTES) {
195 if (tailbufsize < count + BUFSIZ) {
196 tailbufsize = count + BUFSIZ;
197 }
198 }
199 /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
200 * (In fact, it doesn't need ANY memory). So delay allocation.
201 */
202 tailbuf = NULL;
203
204 /* tail the files */
205
206 fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
207 i = 0;
208 do {
209 char *buf;
210 int taillen;
211 int newlines_seen;
212 unsigned seen;
213 int nread;
214 int fd = fds[i];
215
216 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
217 continue; /* may happen with -F */
218
219 if (nfiles > header_threshold) {
220 tail_xprint_header(fmt, argv[i]);
221 fmt = header_fmt_str;
222 }
223
224 if (!G.from_top) {
225 off_t current = lseek(fd, 0, SEEK_END);
226 if (current > 0) {
227 unsigned off;
228 if (COUNT_BYTES) {
229 /* Optimizing count-bytes case if the file is seekable.
230 * Beware of backing up too far.
231 * Also we exclude files with size 0 (because of /proc/xxx) */
232 if (count == 0)
233 continue; /* showing zero bytes is easy :) */
234 current -= count;
235 if (current < 0)
236 current = 0;
237 xlseek(fd, current, SEEK_SET);
238 bb_copyfd_size(fd, STDOUT_FILENO, count);
239 continue;
240 }
241 #if 1 /* This is technically incorrect for *LONG* strings, but very useful */
242 /* Optimizing count-lines case if the file is seekable.
243 * We assume the lines are <64k.
244 * (Users complain that tail takes too long
245 * on multi-gigabyte files) */
246 off = (count | 0xf); /* for small counts, be more paranoid */
247 if (off > (INT_MAX / (64*1024)))
248 off = (INT_MAX / (64*1024));
249 current -= off * (64*1024);
250 if (current < 0)
251 current = 0;
252 xlseek(fd, current, SEEK_SET);
253 #endif
254 }
255 }
256
257 if (!tailbuf)
258 tailbuf = xmalloc(tailbufsize);
259
260 buf = tailbuf;
261 taillen = 0;
262 /* "We saw 1st line/byte".
263 * Used only by +N code ("start from Nth", 1-based): */
264 seen = 1;
265 newlines_seen = 0;
266 while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
267 if (G.from_top) {
268 int nwrite = nread;
269 if (seen < count) {
270 /* We need to skip a few more bytes/lines */
271 if (COUNT_BYTES) {
272 nwrite -= (count - seen);
273 seen += nread;
274 } else {
275 char *s = buf;
276 do {
277 --nwrite;
278 if (*s++ == '\n' && ++seen == count) {
279 break;
280 }
281 } while (nwrite);
282 }
283 }
284 if (nwrite > 0)
285 xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
286 } else if (count) {
287 if (COUNT_BYTES) {
288 taillen += nread;
289 if (taillen > (int)count) {
290 memmove(tailbuf, tailbuf + taillen - count, count);
291 taillen = count;
292 }
293 } else {
294 int k = nread;
295 int newlines_in_buf = 0;
296
297 do { /* count '\n' in last read */
298 k--;
299 if (buf[k] == '\n') {
300 newlines_in_buf++;
301 }
302 } while (k);
303
304 if (newlines_seen + newlines_in_buf < (int)count) {
305 newlines_seen += newlines_in_buf;
306 taillen += nread;
307 } else {
308 int extra = (buf[nread-1] != '\n');
309 char *s;
310
311 k = newlines_seen + newlines_in_buf + extra - count;
312 s = tailbuf;
313 while (k) {
314 if (*s == '\n') {
315 k--;
316 }
317 s++;
318 }
319 taillen += nread - (s - tailbuf);
320 memmove(tailbuf, s, taillen);
321 newlines_seen = count - extra;
322 }
323 if (tailbufsize < (size_t)taillen + BUFSIZ) {
324 tailbufsize = taillen + BUFSIZ;
325 tailbuf = xrealloc(tailbuf, tailbufsize);
326 }
327 }
328 buf = tailbuf + taillen;
329 }
330 } /* while (tail_read() > 0) */
331 if (!G.from_top) {
332 xwrite(STDOUT_FILENO, tailbuf, taillen);
333 }
334 } while (++i < nfiles);
335 prev_fd = fds[i-1];
336
337 tailbuf = xrealloc(tailbuf, BUFSIZ);
338
339 fmt = NULL;
340
341 if (FOLLOW) while (1) {
342 sleep(sleep_period);
343
344 i = 0;
345 do {
346 int nread;
347 const char *filename = argv[i];
348 int fd = fds[i];
349 int new_fd = -1;
350 struct stat sbuf;
351
352 if (FOLLOW_RETRY) {
353 struct stat fsbuf;
354
355 if (fd < 0
356 || fstat(fd, &fsbuf) < 0
357 || stat(filename, &sbuf) < 0
358 || fsbuf.st_dev != sbuf.st_dev
359 || fsbuf.st_ino != sbuf.st_ino
360 ) {
361 /* Looks like file has been created/renamed/deleted */
362 new_fd = open(filename, O_RDONLY);
363 if (new_fd >= 0) {
364 bb_error_msg("%s has %s; following end of new file",
365 filename, (fd < 0) ? "appeared" : "been replaced"
366 );
367 if (fd < 0) {
368 /* No previously open fd for this file,
369 * start using new_fd immediately. */
370 fds[i] = fd = new_fd;
371 new_fd = -1;
372 }
373 } else if (fd >= 0) {
374 bb_perror_msg("%s has been renamed or deleted", filename);
375 }
376 }
377 }
378 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
379 continue;
380 if (nfiles > header_threshold) {
381 fmt = header_fmt_str;
382 }
383 for (;;) {
384 /* tail -f keeps following files even if they are truncated */
385 /* /proc files report zero st_size, don't lseek them */
386 if (fstat(fd, &sbuf) == 0
387 /* && S_ISREG(sbuf.st_mode) TODO? */
388 && sbuf.st_size > 0
389 ) {
390 off_t current = lseek(fd, 0, SEEK_CUR);
391 if (sbuf.st_size < current) {
392 //bb_perror_msg("%s: file truncated", filename); - says coreutils 8.32
393 xlseek(fd, 0, SEEK_SET);
394 }
395 }
396
397 nread = tail_read(fd, tailbuf, BUFSIZ);
398 if (nread <= 0) {
399 if (new_fd < 0)
400 break;
401 /* Switch to "tail -F"ing the new file */
402 xmove_fd(new_fd, fd);
403 new_fd = -1;
404 continue;
405 }
406 if (fmt && (fd != prev_fd)) {
407 tail_xprint_header(fmt, filename);
408 fmt = NULL;
409 prev_fd = fd;
410 }
411 xwrite(STDOUT_FILENO, tailbuf, nread);
412 }
413 } while (++i < nfiles);
414 } /* while (1) */
415
416 if (ENABLE_FEATURE_CLEAN_UP) {
417 free(fds);
418 free(tailbuf);
419 }
420 return G.exitcode;
421 }
422