source: trunk/minix/commands/simple/tail.c@ 15

Last change on this file since 15 was 9, checked in by Mattia Monga, 14 years ago

Minix 3.1.2a
File size: 10.2 KB
Line 
1/* tail - copy the end of a file Author: Norbert Schlenker */
2
3/* Syntax: tail [-f] [-c number | -n number] [file]
4 * tail -[number][c|l][f] [file] (obsolescent)
5 * tail +[number][c|l][f] [file] (obsolescent)
6 * Flags:
7 * -c number Measure starting point in bytes. If number begins
8 * with '+', the starting point is relative to the
9 * the file's beginning. If number begins with '-'
10 * or has no sign, the starting point is relative to
11 * the end of the file.
12 * -f Keep trying to read after EOF on files and FIFOs.
13 * -n number Measure starting point in lines. The number
14 * following the flag has significance similar to
15 * that described for the -c flag.
16 *
17 * If neither -c nor -n are specified, the default is tail -n 10.
18 *
19 * In the obsolescent syntax, an argument with a 'c' following the
20 * (optional) number is equivalent to "-c number" in the standard
21 * syntax, with number including the leading sign ('+' or '-') of the
22 * argument. An argument with 'l' following the number is equivalent
23 * to "-n number" in the standard syntax. If the number is not
24 * specified, 10 is used as the default. If neither 'c' nor 'l' are
25 * specified, 'l' is assumed. The character 'f' may be suffixed to
26 * the argument and is equivalent to specifying "-f" in the standard
27 * syntax. Look for lines marked "OBSOLESCENT".
28 *
29 * If no file is specified, standard input is assumed.
30 *
31 * P1003.2 does not specify tail's behavior when a count of 0 is given.
32 * It also does not specify clearly whether the first byte (line) of a
33 * file should be numbered 0 or 1. Historical behavior is that the
34 * first byte is actually number 1 (contrary to all Unix standards).
35 * Historically, a count of 0 (or -0) results in no output whatsoever,
36 * while a count of +0 results in the entire file being copied (just like
37 * +1). The implementor does not agree with these behaviors, but has
38 * copied them slavishly. Look for lines marked "HISTORICAL".
39 *
40 * Author: Norbert Schlenker
41 * Copyright: None. Released to the public domain.
42 * Reference: P1003.2 section 4.59 (draft 10)
43 * Notes: Under Minix, this program requires chmem =30000.
44 * Bugs: No internationalization support; all messages are in English.
45 */
46
47/* Force visible Posix names */
48#ifndef _POSIX_SOURCE
49#define _POSIX_SOURCE 1
50#endif
51
52/* External interfaces */
53#include <sys/types.h>
54#include <sys/stat.h>
55#include <unistd.h>
56#include <ctype.h>
57#include <stdlib.h>
58#include <stdio.h>
59
60/* External interfaces that should have been standardized into <getopt.h> */
61extern char *optarg;
62extern int optind;
63
64/* We expect this constant to be defined in <limits.h> in a Posix program,
65 * but we'll specify it here just in case it's been left out.
66 */
67#ifndef LINE_MAX
68#define LINE_MAX 2048 /* minimum acceptable lower bound */
69#endif
70
71/* Magic numbers suggested or required by Posix specification */
72#define SUCCESS 0 /* exit code in case of success */
73#define FAILURE 1 /* or failure */
74#define DEFAULT_COUNT 10 /* default number of lines or bytes */
75#define MIN_BUFSIZE (LINE_MAX * DEFAULT_COUNT)
76#define SLEEP_INTERVAL 1 /* sleep for one second intervals with -f */
77
78#define FALSE 0
79#define TRUE 1
80
81/* Internal functions - prototyped under Minix */
82_PROTOTYPE(int main, (int argc, char **argv));
83_PROTOTYPE(int tail, (int count, int bytes, int read_until_killed));
84_PROTOTYPE(int keep_reading, (void));
85_PROTOTYPE(void usage, (void));
86
87int main(argc, argv)
88int argc;
89char *argv[];
90{
91 int cflag = FALSE;
92 int nflag = FALSE;
93 int fflag = FALSE;
94 int number = -DEFAULT_COUNT;
95 char *suffix;
96 int opt;
97 struct stat stat_buf;
98
99/* Determining whether this invocation is via the standard syntax or
100 * via an obsolescent one is a nasty kludge. Here it is, but there is
101 * no pretense at elegance.
102 */
103 if (argc == 1) { /* simple: default read of a pipe */
104 exit(tail(-DEFAULT_COUNT, 0, fflag));
105 }
106 if ((argv[1][0] == '+') || /* OBSOLESCENT */
107 (argv[1][0] == '-' && ((isdigit(argv[1][1])) ||
108 (argv[1][1] == 'l') ||
109 (argv[1][1] == 'c' && argv[1][2] == 'f')))) {
110 --argc; ++argv;
111 if (isdigit(argv[0][1])) {
112 number = (int)strtol(argv[0], &suffix, 10);
113 if (number == 0) { /* HISTORICAL */
114 if (argv[0][0] == '+')
115 number = 1;
116 else
117 exit(SUCCESS);
118 }
119 } else {
120 number = (argv[0][0] == '+') ? DEFAULT_COUNT : -DEFAULT_COUNT;
121 suffix = &(argv[0][1]);
122 }
123 if (*suffix != '\0') {
124 if (*suffix == 'c') {
125 cflag = TRUE;
126 ++suffix;
127 }
128 else
129 if (*suffix == 'l') {
130 nflag = TRUE;
131 ++suffix;
132 }
133 }
134 if (*suffix != '\0') {
135 if (*suffix == 'f') {
136 fflag = TRUE;
137 ++suffix;
138 }
139 }
140 if (*suffix != '\0') { /* bad form: assume to be a file name */
141 number = -DEFAULT_COUNT;
142 cflag = nflag = FALSE;
143 fflag = FALSE;
144 } else {
145 --argc; ++argv;
146 }
147 } else { /* new standard syntax */
148 while ((opt = getopt(argc, argv, "c:fn:")) != EOF) {
149 switch (opt) {
150 case 'c':
151 cflag = TRUE;
152 if (*optarg == '+' || *optarg == '-')
153 number = atoi(optarg);
154 else
155 if (isdigit(*optarg))
156 number = -atoi(optarg);
157 else
158 usage();
159 if (number == 0) { /* HISTORICAL */
160 if (*optarg == '+')
161 number = 1;
162 else
163 exit(SUCCESS);
164 }
165 break;
166 case 'f':
167 fflag = TRUE;
168 break;
169 case 'n':
170 nflag = TRUE;
171 if (*optarg == '+' || *optarg == '-')
172 number = atoi(optarg);
173 else
174 if (isdigit(*optarg))
175 number = -atoi(optarg);
176 else
177 usage();
178 if (number == 0) { /* HISTORICAL */
179 if (*optarg == '+')
180 number = 1;
181 else
182 exit(SUCCESS);
183 }
184 break;
185 default:
186 usage();
187 /* NOTREACHED */
188 }
189 }
190 argc -= optind;
191 argv += optind;
192 }
193
194 if (argc > 1 || /* too many arguments */
195 (cflag && nflag)) { /* both bytes and lines specified */
196 usage();
197 }
198
199 if (argc > 0) { /* an actual file */
200 if (freopen(argv[0], "r", stdin) != stdin) {
201 fputs("tail: could not open ", stderr);
202 fputs(argv[0], stderr);
203 fputs("\n", stderr);
204 exit(FAILURE);
205 }
206 /* There is an optimization possibility here. If a file is being
207 * read, we need not look at the front of it. If we seek backwards
208 * from the end, we can (potentially) avoid looking at most of the
209 * file. Some systems fail when asked to seek backwards to a point
210 * before the start of the file, so we avoid that possibility.
211 */
212 if (number < 0 && fstat(fileno(stdin), &stat_buf) == 0) {
213 long offset = cflag ? (long)number : (long)number * LINE_MAX;
214
215 if (-offset < stat_buf.st_size)
216 fseek(stdin, offset, SEEK_END);
217 }
218 } else {
219 fflag = FALSE; /* force -f off when reading a pipe */
220 }
221 exit(tail(number, cflag, fflag));
222 /* NOTREACHED */
223}
224
225int tail(count, bytes, read_until_killed)
226int count; /* lines or bytes desired */
227int bytes; /* TRUE if we want bytes */
228int read_until_killed; /* keep reading at EOF */
229{
230 int c;
231 char *buf; /* pointer to input buffer */
232 char *buf_end; /* and one past its end */
233 char *start; /* pointer to first desired character in buf */
234 char *finish; /* pointer past last desired character */
235 int wrapped_once = FALSE; /* TRUE after buf has been filled once */
236
237/* This is magic. If count is positive, it means start at the count'th
238 * line or byte, with the first line or byte considered number 1. Thus,
239 * we want to SKIP one less line or byte than the number specified. In
240 * the negative case, we look backward from the end of the file for the
241 * (count + 1)'th newline or byte, so we really want the count to be one
242 * LARGER than was specified (in absolute value). In either case, the
243 * right thing to do is:
244 */
245 --count;
246
247/* Count is positive: skip the desired lines or bytes and then copy. */
248 if (count >= 0) {
249 while (count > 0 && (c = getchar()) != EOF) {
250 if (bytes || c == '\n')
251 --count;
252 }
253 while ((c = getchar()) != EOF) {
254 if (putchar(c) == EOF)
255 return FAILURE;
256 }
257 if (read_until_killed)
258 return keep_reading();
259 return ferror(stdin) ? FAILURE : SUCCESS;
260 }
261
262/* Count is negative: allocate a reasonably large buffer. */
263 if ((buf = (char *)malloc(MIN_BUFSIZE + 1)) == (char *)NULL) {
264 fputs("tail: out of memory\n", stderr);
265 return FAILURE;
266 }
267 buf_end = buf + (MIN_BUFSIZE + 1);
268
269/* Read the entire file into the buffer. */
270 finish = buf;
271 while ((c = getchar()) != EOF) {
272 *finish++ = c;
273 if (finish == buf_end) {
274 finish = buf;
275 wrapped_once = TRUE;
276 }
277 }
278 if (ferror(stdin))
279 return FAILURE;
280
281/* Back up inside the buffer. The count has already been adjusted to
282 * back up exactly one character too far, so we will bump the buffer
283 * pointer once after we're done.
284 *
285 * BUG: For large line counts, the buffer may not be large enough to
286 * hold all the lines. The specification allows the program to
287 * fail in such a case - this program will simply dump the entire
288 * buffer's contents as its best attempt at the desired behavior.
289 */
290 if (finish != buf || wrapped_once) { /* file was not empty */
291 start = (finish == buf) ? buf_end - 1 : finish - 1;
292 while (start != finish) {
293 if ((bytes || *start == '\n') && ++count == 0)
294 break;
295 if (start == buf) {
296 start = buf_end - 1;
297 if (!wrapped_once) /* never wrapped: stop now */
298 break;
299 } else {
300 --start;
301 }
302 }
303 if (++start == buf_end) { /* bump after going too far */
304 start = buf;
305 }
306 if (finish > start) {
307 fwrite(start, 1, finish - start, stdout);
308 } else {
309 fwrite(start, 1, buf_end - start, stdout);
310 fwrite(buf, 1, finish - buf, stdout);
311 }
312 }
313 if (read_until_killed)
314 return keep_reading();
315 return ferror(stdout) ? FAILURE : SUCCESS;
316}
317
318/* Wake at intervals to reread standard input. Copy anything read to
319 * standard output and then go to sleep again.
320 */
321int keep_reading()
322{
323 char buf[1024];
324 int n;
325 int i;
326 off_t pos;
327 struct stat st;
328
329 pos = lseek(0, (off_t) 0, SEEK_CUR);
330 for (;;) {
331 for (i = 0; i < 60; i++) {
332 while ((n = read(0, buf, sizeof(buf))) > 0) {
333 if (write(1, buf, n) < 0) return FAILURE;
334 }
335 if (n < 0) return FAILURE;
336
337 sleep(SLEEP_INTERVAL);
338 }
339
340 /* Rewind if suddenly truncated. */
341 if (pos != -1) {
342 if (fstat(0, &st) == -1) {
343 pos = -1;
344 } else
345 if (st.st_size < pos) {
346 pos = lseek(0, (off_t) 0, SEEK_SET);
347 } else {
348 pos = st.st_size;
349 }
350 }
351 }
352}
353
354/* Tell the user the standard syntax. */
355void usage()
356{
357 fputs("Usage: tail [-f] [-c number | -n number] [file]\n", stderr);
358 exit(FAILURE);
359}
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