1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
|
#include <AK/Assertions.h>
#include <LibCore/CArgsParser.h>
#include <LibCore/CFile.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define DEFAULT_LINE_COUNT 10
int tail_from_pos(CFile& file, off_t startline, bool want_follow)
{
if (!file.seek(startline + 1))
return 1;
while (true) {
const auto& b = file.read(4096);
if (b.is_empty()) {
if (!want_follow) {
break;
} else {
while (!file.can_read()) {
// FIXME: would be nice to have access to can_read_from_fd with an infinite timeout
usleep(100);
}
continue;
}
}
if (write(STDOUT_FILENO, b.pointer(), b.size()) < 0)
return 1;
}
return 0;
}
off_t find_seek_pos(CFile& file, int wanted_lines)
{
// Rather than reading the whole file, start at the end and work backwards,
// stopping when we've found the number of lines we want.
off_t pos = 0;
if (!file.seek(0, CIODevice::SeekMode::FromEndPosition, &pos)) {
fprintf(stderr, "Failed to find end of file: %s\n", file.error_string());
return 1;
}
off_t end = pos;
int lines = 0;
// FIXME: Reading char-by-char is only OK if CIODevice's read buffer
// is smart enough to not read char-by-char. Fix it there, or fix it here :)
for (; pos >= 0; pos--) {
file.seek(pos);
const auto& ch = file.read(1);
if (ch.is_empty()) {
// Presumably the file got truncated?
// Keep trying to read backwards...
} else {
if (*ch.pointer() == '\n' && (end - pos) > 1) {
lines++;
if (lines == wanted_lines)
break;
}
}
}
return pos;
}
int main(int argc, char* argv[])
{
CArgsParser args_parser("tail");
args_parser.add_arg("f", "follow -- appended data is output as it is written to the file");
args_parser.add_arg("n", "lines", "fetch the specified number of lines");
args_parser.add_required_single_value("file");
CArgsParserResult args = args_parser.parse(argc, argv);
Vector<String> values = args.get_single_values();
if (values.size() != 1) {
args_parser.print_usage();
return 1;
}
int line_count = 0;
if (args.is_present("n")) {
line_count = strtol(args.get("n").characters(), NULL, 10);
if (errno == EINVAL) {
args_parser.print_usage();
return 1;
}
} else {
line_count = DEFAULT_LINE_COUNT;
}
CFile f(values[0]);
if (!f.open(CIODevice::ReadOnly)) {
fprintf(stderr, "Error opening file %s: %s\n", f.filename().characters(), strerror(errno));
exit(1);
}
bool flag_follow = args.is_present("f");
auto pos = find_seek_pos(f, line_count);
return tail_from_pos(f, pos, flag_follow);
}
|
