coreutils/tail.c

   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 tarball for details.
   8  */
   9
  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 */
  13
  14 /* Mar 16, 2003      Manuel Novoa III   (mjn3@codepoet.org)
  15  *
  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)
  25  */
  26
  27 #include "busybox.h"
  28
  29 static const struct suffix_mult tail_suffixes[] = {
  30         { "b", 512 },
  31         { "k", 1024 },
  32         { "m", 1024*1024 },
  33         { NULL, 0 }
  34 };
  35
  36 static int status;
  37
  38 static void tail_xprint_header(const char *fmt, const char *filename)
  39 {
  40         if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
  41                 bb_perror_nomsg_and_die();
  42 }
  43
  44 static ssize_t tail_read(int fd, char *buf, size_t count)
  45 {
  46         ssize_t r;
  47         off_t current, end;
  48         struct stat sbuf;
  49
  50         end = current = lseek(fd, 0, SEEK_CUR);
  51         if (!fstat(fd, &sbuf))
  52                 end = sbuf.st_size;
  53         lseek(fd, end < current ? 0 : current, SEEK_SET);
  54         r = safe_read(fd, buf, count);
  55         if (r < 0) {
  56                 bb_perror_msg(bb_msg_read_error);
  57                 status = EXIT_FAILURE;
  58         }
  59
  60         return r;
  61 }
  62
  63 static const char header_fmt[] = "\n==> %s <==\n";
  64
  65 int tail_main(int argc, char **argv)
  66 {
  67         unsigned count = 10;
  68         unsigned sleep_period = 1;
  69         bool from_top = 0;
  70         int header_threshhold = 1;
  71         const char *str_c, *str_n, *str_s;
  72
  73         char *tailbuf;
  74         size_t tailbufsize;
  75         int taillen = 0;
  76         int newline = 0;
  77         int nfiles, nread, nwrite, seen, i, opt;
  78
  79         int *fds;
  80         char *s, *buf;
  81         const char *fmt;
  82
  83         void eat_num(const char *p) {
  84                 if (*p == '-') p++;
  85                 else if (*p == '+') { p++; from_top = 1; }
  86                 count = xatou_sfx(p, tail_suffixes);
  87         }
  88
  89
  90 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
  91         /* Allow legacy syntax of an initial numeric option without -n. */
  92         if (argc >= 2 && (argv[1][0] == '+' || argv[1][0] == '-')
  93          && isdigit(argv[1][1])
  94         ) {
  95                 argv[0] = "-n";
  96                 argv--;
  97                 argc++;
  98         }
  99 #endif
 100
 101         opt = getopt32(argc, argv, "fc:n:" USE_FEATURE_FANCY_TAIL("qs:v"), &str_c, &str_n, &str_s);
 102 #define FOLLOW (opt & 0x1)
 103 #define COUNT_BYTES (opt & 0x2)
 104         //if (opt & 0x1) // -f
 105         if (opt & 0x2) eat_num(str_c); // -c
 106         if (opt & 0x4) eat_num(str_n); // -n
 107 #if ENABLE_FEATURE_FANCY_TAIL
 108         if (opt & 0x8) header_threshhold = INT_MAX; // -q
 109         if (opt & 0x10) sleep_period = xatou(str_s); // -s
 110         if (opt & 0x20) header_threshhold = 0; // -v
 111 #endif
 112         argc -= optind;
 113         argv += optind;
 114
 115         /* open all the files */
 116         fds = xmalloc(sizeof(int) * (argc + 1));
 117         nfiles = i = 0;
 118         if (argc == 0) {
 119                 struct stat statbuf;
 120
 121                 if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
 122                         opt &= ~1; /* clear FOLLOW */
 123                 }
 124                 *argv = (char *) bb_msg_standard_input;
 125                 goto DO_STDIN;
 126         }
 127
 128         do {
 129                 if (NOT_LONE_DASH(argv[i])) {
 130                         fds[nfiles] = open(argv[i], O_RDONLY);
 131                         if (fds[nfiles] < 0) {
 132                                 bb_perror_msg("%s", argv[i]);
 133                                 status = EXIT_FAILURE;
 134                                 continue;
 135                         }
 136                 } else {
 137  DO_STDIN:              /* "-" */
 138                         fds[nfiles] = STDIN_FILENO;
 139                 }
 140                 argv[nfiles] = argv[i];
 141                 ++nfiles;
 142         } while (++i < argc);
 143
 144         if (!nfiles)
 145                 bb_error_msg_and_die("no files");
 146
 147         tailbufsize = BUFSIZ;
 148
 149         /* tail the files */
 150         if (!from_top && COUNT_BYTES) {
 151                 if (tailbufsize < count) {
 152                         tailbufsize = count + BUFSIZ;
 153                 }
 154         }
 155
 156         buf = tailbuf = xmalloc(tailbufsize);
 157
 158         fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
 159         i = 0;
 160         do {
 161                 /* Be careful.  It would be possible to optimize the count-bytes
 162                  * case if the file is seekable.  If you do though, remember that
 163                  * starting file position may not be the beginning of the file.
 164                  * Beware of backing up too far.  See example in wc.c.
 165                  */
 166                 if (!(count | from_top) && lseek(fds[i], 0, SEEK_END) >= 0) {
 167                         continue;
 168                 }
 169
 170                 if (nfiles > header_threshhold) {
 171                         tail_xprint_header(fmt, argv[i]);
 172                         fmt = header_fmt;
 173                 }
 174
 175                 buf = tailbuf;
 176                 taillen = 0;
 177                 seen = 1;
 178                 newline = 0;
 179
 180                 while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
 181                         if (from_top) {
 182                                 nwrite = nread;
 183                                 if (seen < count) {
 184                                         if (COUNT_BYTES) {
 185                                                 nwrite -= (count - seen);
 186                                                 seen = count;
 187                                         } else {
 188                                                 s = buf;
 189                                                 do {
 190                                                         --nwrite;
 191                                                         if (*s++ == '\n' && ++seen == count) {
 192                                                                 break;
 193                                                         }
 194                                                 } while (nwrite);
 195                                         }
 196                                 }
 197                                 xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 198                         } else if (count) {
 199                                 if (COUNT_BYTES) {
 200                                         taillen += nread;
 201                                         if (taillen > count) {
 202                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 203                                                 taillen = count;
 204                                         }
 205                                 } else {
 206                                         int k = nread;
 207                                         int nbuf = 0;
 208
 209                                         while (k) {
 210                                                 --k;
 211                                                 if (buf[k] == '\n') {
 212                                                         ++nbuf;
 213                                                 }
 214                                         }
 215
 216                                         if (newline + nbuf < count) {
 217                                                 newline += nbuf;
 218                                                 taillen += nread;
 219
 220                                         } else {
 221                                                 int extra = 0;
 222                                                 if (buf[nread-1] != '\n') {
 223                                                         extra = 1;
 224                                                 }
 225
 226                                                 k = newline + nbuf + extra - count;
 227                                                 s = tailbuf;
 228                                                 while (k) {
 229                                                         if (*s == '\n') {
 230                                                                 --k;
 231                                                         }
 232                                                         ++s;
 233                                                 }
 234
 235                                                 taillen += nread - (s - tailbuf);
 236                                                 memmove(tailbuf, s, taillen);
 237                                                 newline = count - extra;
 238                                         }
 239                                         if (tailbufsize < taillen + BUFSIZ) {
 240                                                 tailbufsize = taillen + BUFSIZ;
 241                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 242                                         }
 243                                 }
 244                                 buf = tailbuf + taillen;
 245                         }
 246                 }
 247
 248                 if (!from_top) {
 249                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 250                 }
 251
 252                 taillen = 0;
 253         } while (++i < nfiles);
 254
 255         buf = xrealloc(tailbuf, BUFSIZ);
 256
 257         fmt = NULL;
 258
 259         if (FOLLOW) while (1) {
 260                 sleep(sleep_period);
 261                 i = 0;
 262                 do {
 263                         if (nfiles > header_threshhold) {
 264                                 fmt = header_fmt;
 265                         }
 266                         while ((nread = tail_read(fds[i], buf, sizeof(buf))) > 0) {
 267                                 if (fmt) {
 268                                         tail_xprint_header(fmt, argv[i]);
 269                                         fmt = NULL;
 270                                 }
 271                                 xwrite(STDOUT_FILENO, buf, nread);
 272                         }
 273                 } while (++i < nfiles);
 274         }
 275
 276         return status;
 277 }