Harald Arnesen [28.03.2020 15:31]:
> Since my previous attempt at providing a tail command for FreeDOS didn't
> work out, here is another go. Taken directly from 4.3BSD
> <https://www.tuhs.org/Archive/Distributions/UCB/4.3BSD/src.tar.gz>,
> with one small change.
A cleaned-up version. Compiles without errors with Watcom C.
--
Hilsen Harald
/*
* Copyright (c) 1980 Regents of the University of California.
* All rights reserved. The Berkeley software License Agreement
* specifies the terms and conditions for redistribution.
*/
#ifndef lint
char copyright[] =
"@(#) Copyright (c) 1980 Regents of the University of California.\n\
All rights reserved.\n";
#endif
#ifndef lint
char sccsid[] = "@(#)tail.c 5.2 (Berkeley) 1/10/86";
#endif
/* tail command
*
* tail where [file]
* where is +/-n[type]
* - means n lines before end
* + means nth line from beginning
* type 'b' means tail n blocks, not lines
* type 'c' means tail n characters
* Type 'r' means in lines in reverse order from end
* (for -r, default is entire buffer )
* option 'f' means loop endlessly trying to read more
* characters after the end of file, on the assumption
* that the file is growing
*/
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#define LBIN 32769
#undef BUFSIZ
#define BUFSIZ 8192
struct stat statb;
int follow;
int piped;
char bin[LBIN];
int errno;
void fexit(void);
int main(int argc, char **argv)
{
long n, di, i, j, k;
char *arg;
int partial, bylines, bkwds, fromend, lastnl;
char *p;
arg = argv[1];
if (argc <= 1 || (*arg != '-' && *arg != '+')) {
arg = "-10l";
argc++;
argv--;
}
fromend = *arg == '-';
arg++;
if (isdigit(*arg)) {
n = 0;
while (isdigit(*arg))
n = n * 10 + *arg++ - '0';
} else
n = -1;
if (!fromend && n > 0)
n--;
if (argc > 2) {
(void)close(0);
if (open(argv[2], 0) != 0) {
perror(argv[2]);
return EXIT_FAILURE;
}
}
(void)lseek(0, (off_t) 0, SEEK_CUR);
piped = errno == ESPIPE;
bylines = -1;
bkwds = 0;
while (*arg)
switch (*arg++) {
case 'b':
if (n == -1)
n = 1;
n <<= 9;
if (bylines != -1)
goto errcom;
bylines = 0;
break;
case 'c':
if (bylines != -1)
goto errcom;
bylines = 0;
break;
case 'f':
follow = 1;
break;
case 'r':
if (n == -1)
n = LBIN;
bkwds = 1;
fromend = 1;
bylines = 1;
break;
case 'l':
if (bylines != -1)
goto errcom;
bylines = 1;
break;
default:
goto errcom;
}
if (n == -1)
n = 10;
if (bylines == -1)
bylines = 1;
if (bkwds)
follow = 0;
if (fromend)
goto keep;
/*seek from beginning */
if (bylines) {
j = 0;
while (n-- > 0) {
do {
if (j-- <= 0) {
p = bin;
j = read(0, p, BUFSIZ);
if (j-- <= 0)
fexit();
}
} while (*p++ != '\n');
}
(void)write(1, p, j);
} else if (n > 0) {
if (!piped)
(void)fstat(0, &statb);
if (piped || (statb.st_mode & S_IFMT) == S_IFCHR)
while (n > 0) {
i = n > BUFSIZ ? BUFSIZ : n;
i = read(0, bin, i);
if (i <= 0)
fexit();
n -= i;
} else
(void)lseek(0, (off_t) n, SEEK_SET);
}
copy:
while ((i = read(0, bin, BUFSIZ)) > 0)
(void)write(1, bin, i);
fexit();
/*seek from end */
keep:
if (n <= 0)
fexit();
if (!piped) {
(void)fstat(0, &statb);
/* If by lines, back up 1 buffer: else back up as needed */
di = bylines ? LBIN - 1 : n;
if (statb.st_size > di)
(void)lseek(0, (off_t) - di, SEEK_END);
if (!bylines)
goto copy;
}
partial = 1;
for (;;) {
i = 0;
do {
j = read(0, &bin[i], LBIN - i);
if (j <= 0)
goto brka;
i += j;
} while (i < LBIN);
partial = 0;
}
brka:
if (!bylines) {
k = n <= i ? i - n :
partial ? 0 : n >= LBIN ? i + 1 : i - n + LBIN;
k--;
} else {
if (bkwds && bin[i == 0 ? LBIN - 1 : i - 1] != '\n') { /* force trailing newline */
bin[i] = '\n';
if (++i >= LBIN) {
i = 0;
partial = 0;
}
}
k = i;
j = 0;
do {
lastnl = k;
do {
if (--k < 0) {
if (partial) {
if (bkwds)
(void)write(1, bin,
lastnl + 1);
goto brkb;
}
k = LBIN - 1;
}
} while (bin[k] != '\n' && k != i);
if (bkwds && j > 0) {
if (k < lastnl)
(void)write(1, &bin[k + 1], lastnl - k);
else {
(void)write(1, &bin[k + 1],
LBIN - k - 1);
(void)write(1, bin, lastnl + 1);
}
}
} while (j++ < n && k != i);
brkb:
if (bkwds)
return EXIT_FAILURE;
if (k == i)
do {
if (++k >= LBIN)
k = 0;
} while (bin[k] != '\n' && k != i);
}
if (k < i)
(void)write(1, &bin[k + 1], i - k - 1);
else {
(void)write(1, &bin[k + 1], LBIN - k - 1);
(void)write(1, bin, i);
}
fexit();
errcom:
fprintf(stderr, "usage: tail [+_[n][lbc][rf]] [file]\n");
return EXIT_SUCCESS;
}
void fexit()
{
int n;
if (!follow || piped)
exit(0);
for (;;) {
sleep(1);
while ((n = read(0, bin, BUFSIZ)) > 0)
(void)write(1, bin, n);
}
}
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