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 struct globals {
  37         bool status;
  38 };
  39 #define G (*(struct globals*)&bb_common_bufsiz1)
  40
  41 static void tail_xprint_header(const char *fmt, const char *filename)
  42 {
  43         if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
  44                 bb_perror_nomsg_and_die();
  45 }
  46
  47 static ssize_t tail_read(int fd, char *buf, size_t count)
  48 {
  49         ssize_t r;
  50         off_t current, end;
  51         struct stat sbuf;
  52
  53         end = current = lseek(fd, 0, SEEK_CUR);
  54         if (!fstat(fd, &sbuf))
  55                 end = sbuf.st_size;
  56         lseek(fd, end < current ? 0 : current, SEEK_SET);
  57         r = safe_read(fd, buf, count);
  58         if (r < 0) {
  59                 bb_perror_msg(bb_msg_read_error);
  60                 G.status = EXIT_FAILURE;
  61         }
  62
  63         return r;
  64 }
  65
  66 static const char header_fmt[] = "\n==> %s <==\n";
  67
  68 static unsigned eat_num(const char *p) {
  69         if (*p == '-') p++;
  70         else if (*p == '+') { p++; G.status = EXIT_FAILURE; }
  71         return xatou_sfx(p, tail_suffixes);
  72 }
  73
  74 int tail_main(int argc, char **argv);
  75 int tail_main(int argc, char **argv)
  76 {
  77         unsigned count = 10;
  78         unsigned sleep_period = 1;
  79         bool from_top;
  80         int header_threshhold = 1;
  81         const char *str_c, *str_n, *str_s;
  82
  83         char *tailbuf;
  84         size_t tailbufsize;
  85         int taillen = 0;
  86         int newline = 0;
  87         int nfiles, nread, nwrite, seen, i, opt;
  88
  89         int *fds;
  90         char *s, *buf;
  91         const char *fmt;
  92
  93 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
  94         /* Allow legacy syntax of an initial numeric option without -n. */
  95         if (argc >= 2 && (argv[1][0] == '+' || argv[1][0] == '-')
  96          && isdigit(argv[1][1])
  97         ) {
  98                 argv[0] = (char*)"-n";
  99                 argv--;
 100                 argc++;
 101         }
 102 #endif
 103
 104         opt = getopt32(argc, argv, "fc:n:" USE_FEATURE_FANCY_TAIL("qs:v"), &str_c, &str_n, &str_s);
 105 #define FOLLOW (opt & 0x1)
 106 #define COUNT_BYTES (opt & 0x2)
 107         //if (opt & 0x1) // -f
 108         if (opt & 0x2) count = eat_num(str_c); // -c
 109         if (opt & 0x4) count = eat_num(str_n); // -n
 110 #if ENABLE_FEATURE_FANCY_TAIL
 111         if (opt & 0x8) header_threshhold = INT_MAX; // -q
 112         if (opt & 0x10) sleep_period = xatou(str_s); // -s
 113         if (opt & 0x20) header_threshhold = 0; // -v
 114 #endif
 115         argc -= optind;
 116         argv += optind;
 117         from_top = G.status;
 118
 119         /* open all the files */
 120         fds = xmalloc(sizeof(int) * (argc + 1));
 121         nfiles = i = 0;
 122         G.status = EXIT_SUCCESS;
 123         if (argc == 0) {
 124                 struct stat statbuf;
 125
 126                 if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
 127                         opt &= ~1; /* clear FOLLOW */
 128                 }
 129                 *argv = (char *) bb_msg_standard_input;
 130         }
 131         do {
 132                 FILE* fil = fopen_or_warn_stdin(argv[i]);
 133                 if (!fil) {
 134                         G.status = EXIT_FAILURE;
 135                         continue;
 136                 }
 137                 fds[nfiles] = fileno(fil);
 138                 argv[nfiles++] = argv[i];
 139         } while (++i < argc);
 140
 141         if (!nfiles)
 142                 bb_error_msg_and_die("no files");
 143
 144         tailbufsize = BUFSIZ;
 145
 146         /* tail the files */
 147         if (!from_top && COUNT_BYTES) {
 148                 if (tailbufsize < count) {
 149                         tailbufsize = count + BUFSIZ;
 150                 }
 151         }
 152
 153         buf = tailbuf = xmalloc(tailbufsize);
 154
 155         fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
 156         i = 0;
 157         do {
 158                 /* Be careful.  It would be possible to optimize the count-bytes
 159                  * case if the file is seekable.  If you do though, remember that
 160                  * starting file position may not be the beginning of the file.
 161                  * Beware of backing up too far.  See example in wc.c.
 162                  */
 163                 if (!(count | from_top) && lseek(fds[i], 0, SEEK_END) >= 0) {
 164                         continue;
 165                 }
 166
 167                 if (nfiles > header_threshhold) {
 168                         tail_xprint_header(fmt, argv[i]);
 169                         fmt = header_fmt;
 170                 }
 171
 172                 buf = tailbuf;
 173                 taillen = 0;
 174                 seen = 1;
 175                 newline = 0;
 176
 177                 while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
 178                         if (from_top) {
 179                                 nwrite = nread;
 180                                 if (seen < count) {
 181                                         if (COUNT_BYTES) {
 182                                                 nwrite -= (count - seen);
 183                                                 seen = count;
 184                                         } else {
 185                                                 s = buf;
 186                                                 do {
 187                                                         --nwrite;
 188                                                         if (*s++ == '\n' && ++seen == count) {
 189                                                                 break;
 190                                                         }
 191                                                 } while (nwrite);
 192                                         }
 193                                 }
 194                                 xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 195                         } else if (count) {
 196                                 if (COUNT_BYTES) {
 197                                         taillen += nread;
 198                                         if (taillen > count) {
 199                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 200                                                 taillen = count;
 201                                         }
 202                                 } else {
 203                                         int k = nread;
 204                                         int nbuf = 0;
 205
 206                                         while (k) {
 207                                                 --k;
 208                                                 if (buf[k] == '\n') {
 209                                                         ++nbuf;
 210                                                 }
 211                                         }
 212
 213                                         if (newline + nbuf < count) {
 214                                                 newline += nbuf;
 215                                                 taillen += nread;
 216                                         } else {
 217                                                 int extra = 0;
 218
 219                                                 if (buf[nread-1] != '\n')
 220                                                         extra = 1;
 221                                                 k = newline + nbuf + extra - count;
 222                                                 s = tailbuf;
 223                                                 while (k) {
 224                                                         if (*s == '\n') {
 225                                                                 --k;
 226                                                         }
 227                                                         ++s;
 228                                                 }
 229                                                 taillen += nread - (s - tailbuf);
 230                                                 memmove(tailbuf, s, taillen);
 231                                                 newline = count - extra;
 232                                         }
 233                                         if (tailbufsize < taillen + BUFSIZ) {
 234                                                 tailbufsize = taillen + BUFSIZ;
 235                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 236                                         }
 237                                 }
 238                                 buf = tailbuf + taillen;
 239                         }
 240                 }
 241
 242                 if (!from_top) {
 243                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 244                 }
 245
 246                 taillen = 0;
 247         } while (++i < nfiles);
 248
 249         buf = xrealloc(tailbuf, BUFSIZ);
 250
 251         fmt = NULL;
 252
 253         if (FOLLOW) while (1) {
 254                 sleep(sleep_period);
 255                 i = 0;
 256                 do {
 257                         if (nfiles > header_threshhold) {
 258                                 fmt = header_fmt;
 259                         }
 260                         while ((nread = tail_read(fds[i], buf, sizeof(buf))) > 0) {
 261                                 if (fmt) {
 262                                         tail_xprint_header(fmt, argv[i]);
 263                                         fmt = NULL;
 264                                 }
 265                                 xwrite(STDOUT_FILENO, buf, nread);
 266                         }
 267                 } while (++i < nfiles);
 268         }
 269         if (ENABLE_FEATURE_CLEAN_UP) {
 270                 free(fds);
 271         }
 272         return G.status;
 273 }