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 = EXIT_FAILURE;
  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         USE_FEATURE_FANCY_TAIL(const char *str_s;)
  91
  92         char *tailbuf;
  93         size_t tailbufsize;
  94         int taillen = 0;
  95         int newline = 0;
  96         int nfiles, nread, nwrite, seen, i, opt;
  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 (argc >= 2 && (argv[1][0] == '+' || argv[1][0] == '-')
 105          && isdigit(argv[1][1])
 106         ) {
 107                 /* replacing arg[0] with "-n" can segfault, so... */
 108                 argv[1] = xasprintf("-n%s", argv[1]);
 109 #if 0 /* If we ever decide to make tail NOFORK */
 110                 char *s = alloca(strlen(argv[1]) + 3);
 111                 sprintf(s, "-n%s", argv[1]);
 112                 argv[1] = s;
 113 #endif
 114         }
 115 #endif
 116
 117         opt = getopt32(argv, "fc:n:" USE_FEATURE_FANCY_TAIL("qs:v"),
 118                         &str_c, &str_n USE_FEATURE_FANCY_TAIL(,&str_s));
 119 #define FOLLOW (opt & 0x1)
 120 #define COUNT_BYTES (opt & 0x2)
 121         //if (opt & 0x1) // -f
 122         if (opt & 0x2) count = eat_num(str_c); // -c
 123         if (opt & 0x4) count = eat_num(str_n); // -n
 124 #if ENABLE_FEATURE_FANCY_TAIL
 125         if (opt & 0x8) header_threshhold = INT_MAX; // -q
 126         if (opt & 0x10) sleep_period = xatou(str_s); // -s
 127         if (opt & 0x20) header_threshhold = 0; // -v
 128 #endif
 129         argc -= optind;
 130         argv += optind;
 131         from_top = G.status;
 132
 133         /* open all the files */
 134         fds = xmalloc(sizeof(int) * (argc + 1));
 135         nfiles = i = 0;
 136         G.status = EXIT_SUCCESS;
 137         if (argc == 0) {
 138                 struct stat statbuf;
 139
 140                 if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
 141                         opt &= ~1; /* clear FOLLOW */
 142                 }
 143                 *argv = (char *) bb_msg_standard_input;
 144         }
 145         do {
 146                 FILE* fil = fopen_or_warn_stdin(argv[i]);
 147                 if (!fil) {
 148                         G.status = EXIT_FAILURE;
 149                         continue;
 150                 }
 151                 fds[nfiles] = fileno(fil);
 152                 argv[nfiles++] = argv[i];
 153         } while (++i < argc);
 154
 155         if (!nfiles)
 156                 bb_error_msg_and_die("no files");
 157
 158         tailbufsize = BUFSIZ;
 159
 160         /* tail the files */
 161         if (!from_top && COUNT_BYTES) {
 162                 if (tailbufsize < count) {
 163                         tailbufsize = count + BUFSIZ;
 164                 }
 165         }
 166
 167         buf = tailbuf = xmalloc(tailbufsize);
 168
 169         fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
 170         i = 0;
 171         do {
 172                 /* Be careful.  It would be possible to optimize the count-bytes
 173                  * case if the file is seekable.  If you do though, remember that
 174                  * starting file position may not be the beginning of the file.
 175                  * Beware of backing up too far.  See example in wc.c.
 176                  */
 177                 if (!(count | from_top) && lseek(fds[i], 0, SEEK_END) >= 0) {
 178                         continue;
 179                 }
 180
 181                 if (nfiles > header_threshhold) {
 182                         tail_xprint_header(fmt, argv[i]);
 183                         fmt = header_fmt;
 184                 }
 185
 186                 buf = tailbuf;
 187                 taillen = 0;
 188                 seen = 1;
 189                 newline = 0;
 190
 191                 while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
 192                         if (from_top) {
 193                                 nwrite = nread;
 194                                 if (seen < count) {
 195                                         if (COUNT_BYTES) {
 196                                                 nwrite -= (count - seen);
 197                                                 seen = count;
 198                                         } else {
 199                                                 s = buf;
 200                                                 do {
 201                                                         --nwrite;
 202                                                         if (*s++ == '\n' && ++seen == count) {
 203                                                                 break;
 204                                                         }
 205                                                 } while (nwrite);
 206                                         }
 207                                 }
 208                                 xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 209                         } else if (count) {
 210                                 if (COUNT_BYTES) {
 211                                         taillen += nread;
 212                                         if (taillen > count) {
 213                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 214                                                 taillen = count;
 215                                         }
 216                                 } else {
 217                                         int k = nread;
 218                                         int nbuf = 0;
 219
 220                                         while (k) {
 221                                                 --k;
 222                                                 if (buf[k] == '\n') {
 223                                                         ++nbuf;
 224                                                 }
 225                                         }
 226
 227                                         if (newline + nbuf < count) {
 228                                                 newline += nbuf;
 229                                                 taillen += nread;
 230                                         } else {
 231                                                 int extra = 0;
 232
 233                                                 if (buf[nread-1] != '\n')
 234                                                         extra = 1;
 235                                                 k = newline + nbuf + 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                                                 newline = count - extra;
 246                                         }
 247                                         if (tailbufsize < taillen + BUFSIZ) {
 248                                                 tailbufsize = taillen + BUFSIZ;
 249                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 250                                         }
 251                                 }
 252                                 buf = tailbuf + taillen;
 253                         }
 254                 }
 255
 256                 if (!from_top) {
 257                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 258                 }
 259
 260                 taillen = 0;
 261         } while (++i < nfiles);
 262
 263         buf = xrealloc(tailbuf, BUFSIZ);
 264
 265         fmt = NULL;
 266
 267         if (FOLLOW) while (1) {
 268                 sleep(sleep_period);
 269                 i = 0;
 270                 do {
 271                         if (nfiles > header_threshhold) {
 272                                 fmt = header_fmt;
 273                         }
 274                         while ((nread = tail_read(fds[i], buf, BUFSIZ)) > 0) {
 275                                 if (fmt) {
 276                                         tail_xprint_header(fmt, argv[i]);
 277                                         fmt = NULL;
 278                                 }
 279                                 xwrite(STDOUT_FILENO, buf, nread);
 280                         }
 281                 } while (++i < nfiles);
 282         }
 283         if (ENABLE_FEATURE_CLEAN_UP) {
 284                 free(fds);
 285         }
 286         return G.status;
 287 }