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 "libbb.h"
  28
  29 static const struct suffix_mult tail_suffixes[] = {
  30         { "b", 512 },
  31         { "k", 1024 },
  32         { "m", 1024*1024 },
  33         { }
  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;
  51         struct stat sbuf;
  52
  53         /* (A good comment is missing here) */
  54         current = lseek(fd, 0, SEEK_CUR);
  55         /* /proc files report zero st_size, don't lseek them. */
  56         if (fstat(fd, &sbuf) == 0 && sbuf.st_size)
  57                 if (sbuf.st_size < current)
  58                         lseek(fd, 0, SEEK_SET);
  59
  60         r = full_read(fd, buf, count);
  61         if (r < 0) {
  62                 bb_perror_msg(bb_msg_read_error);
  63                 G.status = EXIT_FAILURE;
  64         }
  65
  66         return r;
  67 }
  68
  69 static const char header_fmt[] ALIGN1 = "\n==> %s <==\n";
  70
  71 static unsigned eat_num(const char *p)
  72 {
  73         if (*p == '-')
  74                 p++;
  75         else if (*p == '+') {
  76                 p++;
  77                 G.status = 1; /* mark that we saw "+" */
  78         }
  79         return xatou_sfx(p, tail_suffixes);
  80 }
  81
  82 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  83 int tail_main(int argc, char **argv)
  84 {
  85         unsigned count = 10;
  86         unsigned sleep_period = 1;
  87         bool from_top;
  88         int header_threshhold = 1;
  89         const char *str_c, *str_n;
  90
  91         char *tailbuf;
  92         size_t tailbufsize;
  93         int taillen = 0;
  94         int newlines_seen = 0;
  95         int nfiles, nread, nwrite, i, opt;
  96         unsigned seen;
  97
  98         int *fds;
  99         char *s, *buf;
 100         const char *fmt;
 101
 102 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 103         /* Allow legacy syntax of an initial numeric option without -n. */
 104         if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
 105          && isdigit(argv[1][1])
 106         ) {
 107                 count = eat_num(&argv[1][1]);
 108                 argv++;
 109                 argc--;
 110         }
 111 #endif
 112
 113         USE_FEATURE_FANCY_TAIL(opt_complementary = "s+";) /* -s N */
 114         opt = getopt32(argv, "fc:n:" USE_FEATURE_FANCY_TAIL("qs:v"),
 115                         &str_c, &str_n USE_FEATURE_FANCY_TAIL(,&sleep_period));
 116 #define FOLLOW (opt & 0x1)
 117 #define COUNT_BYTES (opt & 0x2)
 118         //if (opt & 0x1) // -f
 119         if (opt & 0x2) count = eat_num(str_c); // -c
 120         if (opt & 0x4) count = eat_num(str_n); // -n
 121 #if ENABLE_FEATURE_FANCY_TAIL
 122         if (opt & 0x8) header_threshhold = INT_MAX; // -q
 123         if (opt & 0x20) header_threshhold = 0; // -v
 124 #endif
 125         argc -= optind;
 126         argv += optind;
 127         from_top = G.status; /* 1 if there was "-c +N" or "-n +N" */
 128         G.status = EXIT_SUCCESS;
 129
 130         /* open all the files */
 131         fds = xmalloc(sizeof(int) * (argc + 1));
 132         if (!argv[0]) {
 133                 struct stat statbuf;
 134
 135                 if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
 136                         opt &= ~1; /* clear FOLLOW */
 137                 }
 138                 *argv = (char *) bb_msg_standard_input;
 139         }
 140         nfiles = i = 0;
 141         do {
 142                 int fd = open_or_warn_stdin(argv[i]);
 143                 if (fd < 0) {
 144                         G.status = EXIT_FAILURE;
 145                         continue;
 146                 }
 147                 fds[nfiles] = fd;
 148                 argv[nfiles++] = argv[i];
 149         } while (++i < argc);
 150
 151         if (!nfiles)
 152                 bb_error_msg_and_die("no files");
 153
 154         /* prepare the buffer */
 155         tailbufsize = BUFSIZ;
 156         if (!from_top && COUNT_BYTES) {
 157                 if (tailbufsize < count + BUFSIZ) {
 158                         tailbufsize = count + BUFSIZ;
 159                 }
 160         }
 161         tailbuf = xmalloc(tailbufsize);
 162
 163         /* tail the files */
 164         fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
 165         i = 0;
 166         do {
 167                 if (nfiles > header_threshhold) {
 168                         tail_xprint_header(fmt, argv[i]);
 169                         fmt = header_fmt;
 170                 }
 171
 172                 /* Optimizing count-bytes case if the file is seekable.
 173                  * Beware of backing up too far.
 174                  * Also we exclude files with size 0 (because of /proc/xxx) */
 175                 if (COUNT_BYTES && !from_top) {
 176                         off_t current = lseek(fds[i], 0, SEEK_END);
 177                         if (current > 0) {
 178                                 if (count == 0)
 179                                         continue; /* showing zero lines is easy :) */
 180                                 current -= count;
 181                                 if (current < 0)
 182                                         current = 0;
 183                                 xlseek(fds[i], current, SEEK_SET);
 184                                 bb_copyfd_size(fds[i], STDOUT_FILENO, count);
 185                                 continue;
 186                         }
 187                 }
 188
 189                 buf = tailbuf;
 190                 taillen = 0;
 191                 seen = 1;
 192                 newlines_seen = 0;
 193                 while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
 194                         if (from_top) {
 195                                 nwrite = nread;
 196                                 if (seen < count) {
 197                                         if (COUNT_BYTES) {
 198                                                 nwrite -= (count - seen);
 199                                                 seen = count;
 200                                         } else {
 201                                                 s = buf;
 202                                                 do {
 203                                                         --nwrite;
 204                                                         if (*s++ == '\n' && ++seen == count) {
 205                                                                 break;
 206                                                         }
 207                                                 } while (nwrite);
 208                                         }
 209                                 }
 210                                 xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 211                         } else if (count) {
 212                                 if (COUNT_BYTES) {
 213                                         taillen += nread;
 214                                         if (taillen > (int)count) {
 215                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 216                                                 taillen = count;
 217                                         }
 218                                 } else {
 219                                         int k = nread;
 220                                         int newlines_in_buf = 0;
 221
 222                                         do { /* count '\n' in last read */
 223                                                 k--;
 224                                                 if (buf[k] == '\n') {
 225                                                         newlines_in_buf++;
 226                                                 }
 227                                         } while (k);
 228
 229                                         if (newlines_seen + newlines_in_buf < (int)count) {
 230                                                 newlines_seen += newlines_in_buf;
 231                                                 taillen += nread;
 232                                         } else {
 233                                                 int extra = (buf[nread-1] != '\n');
 234
 235                                                 k = newlines_seen + newlines_in_buf + extra - count;
 236                                                 s = tailbuf;
 237                                                 while (k) {
 238                                                         if (*s == '\n') {
 239                                                                 k--;
 240                                                         }
 241                                                         s++;
 242                                                 }
 243                                                 taillen += nread - (s - tailbuf);
 244                                                 memmove(tailbuf, s, taillen);
 245                                                 newlines_seen = count - extra;
 246                                         }
 247                                         if (tailbufsize < (size_t)taillen + BUFSIZ) {
 248                                                 tailbufsize = taillen + BUFSIZ;
 249                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 250                                         }
 251                                 }
 252                                 buf = tailbuf + taillen;
 253                         }
 254                 } /* while (tail_read() > 0) */
 255                 if (!from_top) {
 256                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 257                 }
 258         } while (++i < nfiles);
 259
 260         buf = xrealloc(tailbuf, BUFSIZ);
 261
 262         fmt = NULL;
 263
 264         if (FOLLOW) while (1) {
 265                 sleep(sleep_period);
 266                 i = 0;
 267                 do {
 268                         if (nfiles > header_threshhold) {
 269                                 fmt = header_fmt;
 270                         }
 271                         while ((nread = tail_read(fds[i], buf, BUFSIZ)) > 0) {
 272                                 if (fmt) {
 273                                         tail_xprint_header(fmt, argv[i]);
 274                                         fmt = NULL;
 275                                 }
 276                                 xwrite(STDOUT_FILENO, buf, nread);
 277                         }
 278                 } while (++i < nfiles);
 279         }
 280         if (ENABLE_FEATURE_CLEAN_UP) {
 281                 free(fds);
 282         }
 283         return G.status;
 284 }