busybox/coreutils/tail.c

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/* vi: set sw=4 ts=4: */
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/*
* Mini tail implementation for busybox
*
* Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
*
* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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*/
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/* BB_AUDIT SUSv3 compliant (need fancy for -c) */
/* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
/* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
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/* Mar 16, 2003 Manuel Novoa III (mjn3@codepoet.org)
*
* Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
* Bugs fixed (although I may have forgotten one or two... it was pretty bad)
* 1) mixing printf/write without fflush()ing stdout
* 2) no check that any open files are present
* 3) optstring had -q taking an arg
* 4) no error checking on write in some cases, and a warning even then
* 5) q and s interaction bug
* 6) no check for lseek error
* 7) lseek attempted when count==0 even if arg was +0 (from top)
*/
#include "libbb.h"
static const struct suffix_mult tail_suffixes[] = {
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{ "b", 512 },
{ "k", 1024 },
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{ "m", 1024*1024 },
{ }
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};
struct globals {
bool status;
};
#define G (*(struct globals*)&bb_common_bufsiz1)
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static void tail_xprint_header(const char *fmt, const char *filename)
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{
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if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
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bb_perror_nomsg_and_die();
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}
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static ssize_t tail_read(int fd, char *buf, size_t count)
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{
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ssize_t r;
off_t current;
struct stat sbuf;
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/* (A good comment is missing here) */
current = lseek(fd, 0, SEEK_CUR);
/* /proc files report zero st_size, don't lseek them. */
if (fstat(fd, &sbuf) == 0 && sbuf.st_size)
if (sbuf.st_size < current)
lseek(fd, 0, SEEK_SET);
r = full_read(fd, buf, count);
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if (r < 0) {
bb_perror_msg(bb_msg_read_error);
G.status = EXIT_FAILURE;
}
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return r;
}
static const char header_fmt[] ALIGN1 = "\n==> %s <==\n";
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static unsigned eat_num(const char *p)
{
if (*p == '-')
p++;
else if (*p == '+') {
p++;
G.status = 1; /* mark that we saw "+" */
}
return xatou_sfx(p, tail_suffixes);
}
int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int tail_main(int argc, char **argv)
{
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unsigned count = 10;
unsigned sleep_period = 1;
bool from_top;
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int header_threshhold = 1;
const char *str_c, *str_n;
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char *tailbuf;
size_t tailbufsize;
int taillen = 0;
int newlines_seen = 0;
int nfiles, nread, nwrite, i, opt;
unsigned seen;
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int *fds;
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char *s, *buf;
const char *fmt;
#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
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/* Allow legacy syntax of an initial numeric option without -n. */
if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
&& isdigit(argv[1][1])
) {
count = eat_num(argv[1]);
argv++;
argc--;
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}
#endif
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IF_FEATURE_FANCY_TAIL(opt_complementary = "s+";) /* -s N */
opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:v"),
&str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
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#define FOLLOW (opt & 0x1)
#define COUNT_BYTES (opt & 0x2)
//if (opt & 0x1) // -f
if (opt & 0x2) count = eat_num(str_c); // -c
if (opt & 0x4) count = eat_num(str_n); // -n
#if ENABLE_FEATURE_FANCY_TAIL
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if (opt & 0x8) header_threshhold = INT_MAX; // -q
if (opt & 0x20) header_threshhold = 0; // -v
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#endif
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argc -= optind;
argv += optind;
from_top = G.status; /* 1 if there was "-c +N" or "-n +N" */
G.status = EXIT_SUCCESS;
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/* open all the files */
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fds = xmalloc(sizeof(int) * (argc + 1));
if (!argv[0]) {
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struct stat statbuf;
if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
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opt &= ~1; /* clear FOLLOW */
}
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*argv = (char *) bb_msg_standard_input;
}
nfiles = i = 0;
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do {
int fd = open_or_warn_stdin(argv[i]);
if (fd < 0) {
G.status = EXIT_FAILURE;
continue;
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}
fds[nfiles] = fd;
argv[nfiles++] = argv[i];
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} while (++i < argc);
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if (!nfiles)
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bb_error_msg_and_die("no files");
/* prepare the buffer */
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tailbufsize = BUFSIZ;
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if (!from_top && COUNT_BYTES) {
if (tailbufsize < count + BUFSIZ) {
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tailbufsize = count + BUFSIZ;
}
}
tailbuf = xmalloc(tailbufsize);
/* tail the files */
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fmt = header_fmt + 1; /* Skip header leading newline on first output. */
i = 0;
do {
if (nfiles > header_threshhold) {
tail_xprint_header(fmt, argv[i]);
fmt = header_fmt;
}
/* Optimizing count-bytes case if the file is seekable.
* Beware of backing up too far.
* Also we exclude files with size 0 (because of /proc/xxx) */
if (COUNT_BYTES && !from_top) {
off_t current = lseek(fds[i], 0, SEEK_END);
if (current > 0) {
if (count == 0)
continue; /* showing zero lines is easy :) */
current -= count;
if (current < 0)
current = 0;
xlseek(fds[i], current, SEEK_SET);
bb_copyfd_size(fds[i], STDOUT_FILENO, count);
continue;
}
}
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buf = tailbuf;
taillen = 0;
seen = 1;
newlines_seen = 0;
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while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
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if (from_top) {
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nwrite = nread;
if (seen < count) {
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if (COUNT_BYTES) {
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nwrite -= (count - seen);
seen = count;
} else {
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s = buf;
do {
--nwrite;
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if (*s++ == '\n' && ++seen == count) {
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break;
}
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} while (nwrite);
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}
}
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xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
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} else if (count) {
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if (COUNT_BYTES) {
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taillen += nread;
if (taillen > (int)count) {
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memmove(tailbuf, tailbuf + taillen - count, count);
taillen = count;
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}
} else {
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int k = nread;
int newlines_in_buf = 0;
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do { /* count '\n' in last read */
k--;
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if (buf[k] == '\n') {
newlines_in_buf++;
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}
} while (k);
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if (newlines_seen + newlines_in_buf < (int)count) {
newlines_seen += newlines_in_buf;
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taillen += nread;
} else {
int extra = (buf[nread-1] != '\n');
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k = newlines_seen + newlines_in_buf + extra - count;
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s = tailbuf;
while (k) {
if (*s == '\n') {
k--;
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}
s++;
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}
taillen += nread - (s - tailbuf);
memmove(tailbuf, s, taillen);
newlines_seen = count - extra;
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}
if (tailbufsize < (size_t)taillen + BUFSIZ) {
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tailbufsize = taillen + BUFSIZ;
tailbuf = xrealloc(tailbuf, tailbufsize);
}
}
buf = tailbuf + taillen;
}
} /* while (tail_read() > 0) */
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if (!from_top) {
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xwrite(STDOUT_FILENO, tailbuf, taillen);
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}
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} while (++i < nfiles);
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buf = xrealloc(tailbuf, BUFSIZ);
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fmt = NULL;
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if (FOLLOW) while (1) {
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sleep(sleep_period);
i = 0;
do {
if (nfiles > header_threshhold) {
fmt = header_fmt;
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}
while ((nread = tail_read(fds[i], buf, BUFSIZ)) > 0) {
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if (fmt) {
tail_xprint_header(fmt, argv[i]);
fmt = NULL;
}
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xwrite(STDOUT_FILENO, buf, nread);
}
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} while (++i < nfiles);
}
if (ENABLE_FEATURE_CLEAN_UP) {
free(fds);
}
return G.status;
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}