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, 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[] ALIGN1 = "\n==> %s <==\n";
  67
  68 static unsigned eat_num(const char *p)
  69 {
  70         if (*p == '-') p++;
  71         else if (*p == '+') { p++; G.status = EXIT_FAILURE; }
  72         return xatou_sfx(p, tail_suffixes);
  73 }
  74
  75 int tail_main(int argc, char **argv);
  76 int tail_main(int argc, char **argv)
  77 {
  78         unsigned count = 10;
  79         unsigned sleep_period = 1;
  80         bool from_top;
  81         int header_threshhold = 1;
  82         const char *str_c, *str_n;
  83         USE_FEATURE_FANCY_TAIL(const char *str_s;)
  84
  85         char *tailbuf;
  86         size_t tailbufsize;
  87         int taillen = 0;
  88         int newline = 0;
  89         int nfiles, nread, nwrite, seen, i, opt;
  90
  91         int *fds;
  92         char *s, *buf;
  93         const char *fmt;
  94
  95 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
  96         /* Allow legacy syntax of an initial numeric option without -n. */
  97         if (argc >= 2 && (argv[1][0] == '+' || argv[1][0] == '-')
  98          && isdigit(argv[1][1])
  99         ) {
 100                 /* replacing arg[0] with "-n" can segfault, so... */
 101                 argv[1] = xasprintf("-n%s", argv[1]);
 102 #if 0 /* If we ever decide to make tail NOFORK */
 103                 char *s = alloca(strlen(argv[1]) + 3);
 104                 sprintf(s, "-n%s", argv[1]);
 105                 argv[1] = s;
 106 #endif
 107         }
 108 #endif
 109
 110         opt = getopt32(argc, argv, "fc:n:" USE_FEATURE_FANCY_TAIL("qs:v"),
 111                         &str_c, &str_n USE_FEATURE_FANCY_TAIL(,&str_s));
 112 #define FOLLOW (opt & 0x1)
 113 #define COUNT_BYTES (opt & 0x2)
 114         //if (opt & 0x1) // -f
 115         if (opt & 0x2) count = eat_num(str_c); // -c
 116         if (opt & 0x4) count = eat_num(str_n); // -n
 117 #if ENABLE_FEATURE_FANCY_TAIL
 118         if (opt & 0x8) header_threshhold = INT_MAX; // -q
 119         if (opt & 0x10) sleep_period = xatou(str_s); // -s
 120         if (opt & 0x20) header_threshhold = 0; // -v
 121 #endif
 122         argc -= optind;
 123         argv += optind;
 124         from_top = G.status;
 125
 126         /* open all the files */
 127         fds = xmalloc(sizeof(int) * (argc + 1));
 128         nfiles = i = 0;
 129         G.status = EXIT_SUCCESS;
 130         if (argc == 0) {
 131                 struct stat statbuf;
 132
 133                 if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
 134                         opt &= ~1; /* clear FOLLOW */
 135                 }
 136                 *argv = (char *) bb_msg_standard_input;
 137         }
 138         do {
 139                 FILE* fil = fopen_or_warn_stdin(argv[i]);
 140                 if (!fil) {
 141                         G.status = EXIT_FAILURE;
 142                         continue;
 143                 }
 144                 fds[nfiles] = fileno(fil);
 145                 argv[nfiles++] = argv[i];
 146         } while (++i < argc);
 147
 148         if (!nfiles)
 149                 bb_error_msg_and_die("no files");
 150
 151         tailbufsize = BUFSIZ;
 152
 153         /* tail the files */
 154         if (!from_top && COUNT_BYTES) {
 155                 if (tailbufsize < count) {
 156                         tailbufsize = count + BUFSIZ;
 157                 }
 158         }
 159
 160         buf = tailbuf = xmalloc(tailbufsize);
 161
 162         fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
 163         i = 0;
 164         do {
 165                 /* Be careful.  It would be possible to optimize the count-bytes
 166                  * case if the file is seekable.  If you do though, remember that
 167                  * starting file position may not be the beginning of the file.
 168                  * Beware of backing up too far.  See example in wc.c.
 169                  */
 170                 if (!(count | from_top) && lseek(fds[i], 0, SEEK_END) >= 0) {
 171                         continue;
 172                 }
 173
 174                 if (nfiles > header_threshhold) {
 175                         tail_xprint_header(fmt, argv[i]);
 176                         fmt = header_fmt;
 177                 }
 178
 179                 buf = tailbuf;
 180                 taillen = 0;
 181                 seen = 1;
 182                 newline = 0;
 183
 184                 while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
 185                         if (from_top) {
 186                                 nwrite = nread;
 187                                 if (seen < count) {
 188                                         if (COUNT_BYTES) {
 189                                                 nwrite -= (count - seen);
 190                                                 seen = count;
 191                                         } else {
 192                                                 s = buf;
 193                                                 do {
 194                                                         --nwrite;
 195                                                         if (*s++ == '\n' && ++seen == count) {
 196                                                                 break;
 197                                                         }
 198                                                 } while (nwrite);
 199                                         }
 200                                 }
 201                                 xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 202                         } else if (count) {
 203                                 if (COUNT_BYTES) {
 204                                         taillen += nread;
 205                                         if (taillen > count) {
 206                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 207                                                 taillen = count;
 208                                         }
 209                                 } else {
 210                                         int k = nread;
 211                                         int nbuf = 0;
 212
 213                                         while (k) {
 214                                                 --k;
 215                                                 if (buf[k] == '\n') {
 216                                                         ++nbuf;
 217                                                 }
 218                                         }
 219
 220                                         if (newline + nbuf < count) {
 221                                                 newline += nbuf;
 222                                                 taillen += nread;
 223                                         } else {
 224                                                 int extra = 0;
 225
 226                                                 if (buf[nread-1] != '\n')
 227                                                         extra = 1;
 228                                                 k = newline + nbuf + extra - count;
 229                                                 s = tailbuf;
 230                                                 while (k) {
 231                                                         if (*s == '\n') {
 232                                                                 --k;
 233                                                         }
 234                                                         ++s;
 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         if (ENABLE_FEATURE_CLEAN_UP) {
 277                 free(fds);
 278         }
 279         return G.status;
 280 }