LXR busybox/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 source tree.
   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//usage:#define tail_trivial_usage
  28//usage:       "[OPTIONS] [FILE]..."
  29//usage:#define tail_full_usage "\n\n"
  30//usage:       "Print last 10 lines of each FILE (or stdin) to stdout.\n"
  31//usage:       "With more than one FILE, precede each with a filename header.\n"
  32//usage:     "\n        -f              Print data as file grows"
  33//usage:        IF_FEATURE_FANCY_TAIL(
  34//usage:     "\n        -s SECONDS      Wait SECONDS between reads with -f"
  35//usage:        )
  36//usage:     "\n        -n N[kbm]       Print last N lines"
  37//usage:        IF_FEATURE_FANCY_TAIL(
  38//usage:     "\n        -c N[kbm]       Print last N bytes"
  39//usage:     "\n        -q              Never print headers"
  40//usage:     "\n        -v              Always print headers"
  41//usage:     "\n"
  42//usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
  43//usage:     "\nIf N starts with a '+', output begins with the Nth item from the start"
  44//usage:     "\nof each file, not from the end."
  45//usage:        )
  46//usage:
  47//usage:#define tail_example_usage
  48//usage:       "$ tail -n 1 /etc/resolv.conf\n"
  49//usage:       "nameserver 10.0.0.1\n"
  50
  51#include "libbb.h"
  52
  53static const struct suffix_mult tail_suffixes[] = {
  54        { "b", 512 },
  55        { "k", 1024 },
  56        { "m", 1024*1024 },
  57        { "", 0 }
  58};
  59
  60struct globals {
  61        bool from_top;
  62        bool exitcode;
  63} FIX_ALIASING;
  64#define G (*(struct globals*)&bb_common_bufsiz1)
  65
  66static void tail_xprint_header(const char *fmt, const char *filename)
  67{
  68        if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
  69                bb_perror_nomsg_and_die();
  70}
  71
  72static ssize_t tail_read(int fd, char *buf, size_t count)
  73{
  74        ssize_t r;
  75        off_t current;
  76        struct stat sbuf;
  77
  78        /* /proc files report zero st_size, don't lseek them. */
  79        if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
  80                current = lseek(fd, 0, SEEK_CUR);
  81                if (sbuf.st_size < current)
  82                        xlseek(fd, 0, SEEK_SET);
  83        }
  84
  85        r = full_read(fd, buf, count);
  86        if (r < 0) {
  87                bb_perror_msg(bb_msg_read_error);
  88                G.exitcode = EXIT_FAILURE;
  89        }
  90
  91        return r;
  92}
  93
  94#define header_fmt_str "\n==> %s <==\n"
  95
  96static unsigned eat_num(const char *p)
  97{
  98        if (*p == '-')
  99                p++;
 100        else if (*p == '+') {
 101                p++;
 102                G.from_top = 1;
 103        }
 104        return xatou_sfx(p, tail_suffixes);
 105}
 106
 107int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 108int tail_main(int argc, char **argv)
 109{
 110        unsigned count = 10;
 111        unsigned sleep_period = 1;
 112        const char *str_c, *str_n;
 113
 114        char *tailbuf;
 115        size_t tailbufsize;
 116        unsigned header_threshhold = 1;
 117        unsigned nfiles;
 118        int i, opt;
 119
 120        int *fds;
 121        const char *fmt;
 122
 123#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 124        /* Allow legacy syntax of an initial numeric option without -n. */
 125        if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
 126         && isdigit(argv[1][1])
 127        ) {
 128                count = eat_num(argv[1]);
 129                argv++;
 130                argc--;
 131        }
 132#endif
 133
 134        /* -s NUM, -F imlies -f */
 135        IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
 136        opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
 137                        &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
 138#define FOLLOW (opt & 0x1)
 139#define COUNT_BYTES (opt & 0x2)
 140        //if (opt & 0x1) // -f
 141        if (opt & 0x2) count = eat_num(str_c); // -c
 142        if (opt & 0x4) count = eat_num(str_n); // -n
 143#if ENABLE_FEATURE_FANCY_TAIL
 144        /* q: make it impossible for nfiles to be > header_threshhold */
 145        if (opt & 0x8) header_threshhold = UINT_MAX; // -q
 146        //if (opt & 0x10) // -s
 147        if (opt & 0x20) header_threshhold = 0; // -v
 148# define FOLLOW_RETRY (opt & 0x40)
 149#else
 150# define FOLLOW_RETRY 0
 151#endif
 152        argc -= optind;
 153        argv += optind;
 154
 155        /* open all the files */
 156        fds = xmalloc(sizeof(fds[0]) * (argc + 1));
 157        if (!argv[0]) {
 158                struct stat statbuf;
 159
 160                if (fstat(STDIN_FILENO, &statbuf) == 0
 161                 && S_ISFIFO(statbuf.st_mode)
 162                ) {
 163                        opt &= ~1; /* clear FOLLOW */
 164                }
 165                argv[0] = (char *) bb_msg_standard_input;
 166        }
 167        nfiles = i = 0;
 168        do {
 169                int fd = open_or_warn_stdin(argv[i]);
 170                if (fd < 0 && !FOLLOW_RETRY) {
 171                        G.exitcode = EXIT_FAILURE;
 172                        continue;
 173                }
 174                fds[nfiles] = fd;
 175                argv[nfiles++] = argv[i];
 176        } while (++i < argc);
 177
 178        if (!nfiles)
 179                bb_error_msg_and_die("no files");
 180
 181        /* prepare the buffer */
 182        tailbufsize = BUFSIZ;
 183        if (!G.from_top && COUNT_BYTES) {
 184                if (tailbufsize < count + BUFSIZ) {
 185                        tailbufsize = count + BUFSIZ;
 186                }
 187        }
 188        /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
 189         * (In fact, it doesn't need ANY memory). So delay allocation.
 190         */
 191        tailbuf = NULL;
 192
 193        /* tail the files */
 194
 195        fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
 196        i = 0;
 197        do {
 198                char *buf;
 199                int taillen;
 200                int newlines_seen;
 201                unsigned seen;
 202                int nread;
 203                int fd = fds[i];
 204
 205                if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 206                        continue; /* may happen with -E */
 207
 208                if (nfiles > header_threshhold) {
 209                        tail_xprint_header(fmt, argv[i]);
 210                        fmt = header_fmt_str;
 211                }
 212
 213                if (!G.from_top) {
 214                        off_t current = lseek(fd, 0, SEEK_END);
 215                        if (current > 0) {
 216                                unsigned off;
 217                                if (COUNT_BYTES) {
 218                                /* Optimizing count-bytes case if the file is seekable.
 219                                 * Beware of backing up too far.
 220                                 * Also we exclude files with size 0 (because of /proc/xxx) */
 221                                        if (count == 0)
 222                                                continue; /* showing zero bytes is easy :) */
 223                                        current -= count;
 224                                        if (current < 0)
 225                                                current = 0;
 226                                        xlseek(fd, current, SEEK_SET);
 227                                        bb_copyfd_size(fd, STDOUT_FILENO, count);
 228                                        continue;
 229                                }
 230#if 1 /* This is technically incorrect for *LONG* strings, but very useful */
 231                                /* Optimizing count-lines case if the file is seekable.
 232                                 * We assume the lines are <64k.
 233                                 * (Users complain that tail takes too long
 234                                 * on multi-gigabyte files) */
 235                                off = (count | 0xf); /* for small counts, be more paranoid */
 236                                if (off > (INT_MAX / (64*1024)))
 237                                        off = (INT_MAX / (64*1024));
 238                                current -= off * (64*1024);
 239                                if (current < 0)
 240                                        current = 0;
 241                                xlseek(fd, current, SEEK_SET);
 242#endif
 243                        }
 244                }
 245
 246                if (!tailbuf)
 247                        tailbuf = xmalloc(tailbufsize);
 248
 249                buf = tailbuf;
 250                taillen = 0;
 251                /* "We saw 1st line/byte".
 252                 * Used only by +N code ("start from Nth", 1-based): */
 253                seen = 1;
 254                newlines_seen = 0;
 255                while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
 256                        if (G.from_top) {
 257                                int nwrite = nread;
 258                                if (seen < count) {
 259                                        /* We need to skip a few more bytes/lines */
 260                                        if (COUNT_BYTES) {
 261                                                nwrite -= (count - seen);
 262                                                seen = count;
 263                                        } else {
 264                                                char *s = buf;
 265                                                do {
 266                                                        --nwrite;
 267                                                        if (*s++ == '\n' && ++seen == count) {
 268                                                                break;
 269                                                        }
 270                                                } while (nwrite);
 271                                        }
 272                                }
 273                                if (nwrite > 0)
 274                                        xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 275                        } else if (count) {
 276                                if (COUNT_BYTES) {
 277                                        taillen += nread;
 278                                        if (taillen > (int)count) {
 279                                                memmove(tailbuf, tailbuf + taillen - count, count);
 280                                                taillen = count;
 281                                        }
 282                                } else {
 283                                        int k = nread;
 284                                        int newlines_in_buf = 0;
 285
 286                                        do { /* count '\n' in last read */
 287                                                k--;
 288                                                if (buf[k] == '\n') {
 289                                                        newlines_in_buf++;
 290                                                }
 291                                        } while (k);
 292
 293                                        if (newlines_seen + newlines_in_buf < (int)count) {
 294                                                newlines_seen += newlines_in_buf;
 295                                                taillen += nread;
 296                                        } else {
 297                                                int extra = (buf[nread-1] != '\n');
 298                                                char *s;
 299
 300                                                k = newlines_seen + newlines_in_buf + extra - count;
 301                                                s = tailbuf;
 302                                                while (k) {
 303                                                        if (*s == '\n') {
 304                                                                k--;
 305                                                        }
 306                                                        s++;
 307                                                }
 308                                                taillen += nread - (s - tailbuf);
 309                                                memmove(tailbuf, s, taillen);
 310                                                newlines_seen = count - extra;
 311                                        }
 312                                        if (tailbufsize < (size_t)taillen + BUFSIZ) {
 313                                                tailbufsize = taillen + BUFSIZ;
 314                                                tailbuf = xrealloc(tailbuf, tailbufsize);
 315                                        }
 316                                }
 317                                buf = tailbuf + taillen;
 318                        }
 319                } /* while (tail_read() > 0) */
 320                if (!G.from_top) {
 321                        xwrite(STDOUT_FILENO, tailbuf, taillen);
 322                }
 323        } while (++i < nfiles);
 324
 325        tailbuf = xrealloc(tailbuf, BUFSIZ);
 326
 327        fmt = NULL;
 328
 329        if (FOLLOW) while (1) {
 330                sleep(sleep_period);
 331
 332                i = 0;
 333                do {
 334                        int nread;
 335                        const char *filename = argv[i];
 336                        int fd = fds[i];
 337
 338                        if (FOLLOW_RETRY) {
 339                                struct stat sbuf, fsbuf;
 340
 341                                if (fd < 0
 342                                 || fstat(fd, &fsbuf) < 0
 343                                 || stat(filename, &sbuf) < 0
 344                                 || fsbuf.st_dev != sbuf.st_dev
 345                                 || fsbuf.st_ino != sbuf.st_ino
 346                                ) {
 347                                        int new_fd;
 348
 349                                        if (fd >= 0)
 350                                                close(fd);
 351                                        new_fd = open(filename, O_RDONLY);
 352                                        if (new_fd >= 0) {
 353                                                bb_error_msg("%s has %s; following end of new file",
 354                                                        filename, (fd < 0) ? "appeared" : "been replaced"
 355                                                );
 356                                        } else if (fd >= 0) {
 357                                                bb_perror_msg("%s has become inaccessible", filename);
 358                                        }
 359                                        fds[i] = fd = new_fd;
 360                                }
 361                        }
 362                        if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 363                                continue;
 364                        if (nfiles > header_threshhold) {
 365                                fmt = header_fmt_str;
 366                        }
 367                        while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
 368                                if (fmt) {
 369                                        tail_xprint_header(fmt, filename);
 370                                        fmt = NULL;
 371                                }
 372                                xwrite(STDOUT_FILENO, tailbuf, nread);
 373                        }
 374                } while (++i < nfiles);
 375        } /* while (1) */
 376
 377        if (ENABLE_FEATURE_CLEAN_UP) {
 378                free(fds);
 379                free(tailbuf);
 380        }
 381        return G.exitcode;
 382}
 383