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 static unsigned eat_num(const char *p) {
  66         if (*p == '-') p++;
  67         else if (*p == '+') { p++; status = 1; }
  68         return xatou_sfx(p, tail_suffixes);
  69 }
  70
  71 int tail_main(int argc, char **argv);
  72 int tail_main(int argc, char **argv)
  73 {
  74         unsigned count = 10;
  75         unsigned sleep_period = 1;
  76         bool from_top;
  77         int header_threshhold = 1;
  78         const char *str_c, *str_n, *str_s;
  79
  80         char *tailbuf;
  81         size_t tailbufsize;
  82         int taillen = 0;
  83         int newline = 0;
  84         int nfiles, nread, nwrite, seen, i, opt;
  85
  86         int *fds;
  87         char *s, *buf;
  88         const char *fmt;
  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] = (char*)"-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) count = eat_num(str_c); // -c
 106         if (opt & 0x4) count = 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         from_top = status;
 115
 116         /* open all the files */
 117         fds = xmalloc(sizeof(int) * (argc + 1));
 118         status = nfiles = i = 0;
 119         if (argc == 0) {
 120                 struct stat statbuf;
 121
 122                 if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
 123                         opt &= ~1; /* clear FOLLOW */
 124                 }
 125                 *argv = (char *) bb_msg_standard_input;
 126                 goto DO_STDIN;
 127         }
 128
 129         do {
 130                 if (NOT_LONE_DASH(argv[i])) {
 131                         fds[nfiles] = open(argv[i], O_RDONLY);
 132                         if (fds[nfiles] < 0) {
 133                                 bb_perror_msg("%s", argv[i]);
 134                                 status = EXIT_FAILURE;
 135                                 continue;
 136                         }
 137                 } else {
 138  DO_STDIN:              /* "-" */
 139                         fds[nfiles] = STDIN_FILENO;
 140                 }
 141                 argv[nfiles] = argv[i];
 142                 ++nfiles;
 143         } while (++i < argc);
 144
 145         if (!nfiles)
 146                 bb_error_msg_and_die("no files");
 147
 148         tailbufsize = BUFSIZ;
 149
 150         /* tail the files */
 151         if (!from_top && COUNT_BYTES) {
 152                 if (tailbufsize < count) {
 153                         tailbufsize = count + BUFSIZ;
 154                 }
 155         }
 156
 157         buf = tailbuf = xmalloc(tailbufsize);
 158
 159         fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
 160         i = 0;
 161         do {
 162                 /* Be careful.  It would be possible to optimize the count-bytes
 163                  * case if the file is seekable.  If you do though, remember that
 164                  * starting file position may not be the beginning of the file.
 165                  * Beware of backing up too far.  See example in wc.c.
 166                  */
 167                 if (!(count | from_top) && lseek(fds[i], 0, SEEK_END) >= 0) {
 168                         continue;
 169                 }
 170
 171                 if (nfiles > header_threshhold) {
 172                         tail_xprint_header(fmt, argv[i]);
 173                         fmt = header_fmt;
 174                 }
 175
 176                 buf = tailbuf;
 177                 taillen = 0;
 178                 seen = 1;
 179                 newline = 0;
 180
 181                 while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
 182                         if (from_top) {
 183                                 nwrite = nread;
 184                                 if (seen < count) {
 185                                         if (COUNT_BYTES) {
 186                                                 nwrite -= (count - seen);
 187                                                 seen = count;
 188                                         } else {
 189                                                 s = buf;
 190                                                 do {
 191                                                         --nwrite;
 192                                                         if (*s++ == '\n' && ++seen == count) {
 193                                                                 break;
 194                                                         }
 195                                                 } while (nwrite);
 196                                         }
 197                                 }
 198                                 xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 199                         } else if (count) {
 200                                 if (COUNT_BYTES) {
 201                                         taillen += nread;
 202                                         if (taillen > count) {
 203                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 204                                                 taillen = count;
 205                                         }
 206                                 } else {
 207                                         int k = nread;
 208                                         int nbuf = 0;
 209
 210                                         while (k) {
 211                                                 --k;
 212                                                 if (buf[k] == '\n') {
 213                                                         ++nbuf;
 214                                                 }
 215                                         }
 216
 217                                         if (newline + nbuf < count) {
 218                                                 newline += nbuf;
 219                                                 taillen += nread;
 220
 221                                         } else {
 222                                                 int extra = 0;
 223                                                 if (buf[nread-1] != '\n') {
 224                                                         extra = 1;
 225                                                 }
 226
 227                                                 k = newline + nbuf + extra - count;
 228                                                 s = tailbuf;
 229                                                 while (k) {
 230                                                         if (*s == '\n') {
 231                                                                 --k;
 232                                                         }
 233                                                         ++s;
 234                                                 }
 235
 236                                                 taillen += nread - (s - tailbuf);
 237                                                 memmove(tailbuf, s, taillen);
 238                                                 newline = count - extra;
 239                                         }
 240                                         if (tailbufsize < taillen + BUFSIZ) {
 241                                                 tailbufsize = taillen + BUFSIZ;
 242                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 243                                         }
 244                                 }
 245                                 buf = tailbuf + taillen;
 246                         }
 247                 }
 248
 249                 if (!from_top) {
 250                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 251                 }
 252
 253                 taillen = 0;
 254         } while (++i < nfiles);
 255
 256         buf = xrealloc(tailbuf, BUFSIZ);
 257
 258         fmt = NULL;
 259
 260         if (FOLLOW) while (1) {
 261                 sleep(sleep_period);
 262                 i = 0;
 263                 do {
 264                         if (nfiles > header_threshhold) {
 265                                 fmt = header_fmt;
 266                         }
 267                         while ((nread = tail_read(fds[i], buf, sizeof(buf))) > 0) {
 268                                 if (fmt) {
 269                                         tail_xprint_header(fmt, argv[i]);
 270                                         fmt = NULL;
 271                                 }
 272                                 xwrite(STDOUT_FILENO, buf, nread);
 273                         }
 274                 } while (++i < nfiles);
 275         }
 276
 277         return status;
 278 }