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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <LibCore/ArgsParser.h>
#include <LibCore/File.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define DEFAULT_LINE_COUNT 10
static int tail_from_pos(Core::File& 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.data(), b.size()) < 0)
return 1;
}
return 0;
}
static off_t find_seek_pos(Core::File& 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, Core::SeekMode::FromEndPosition, &pos)) {
warnln("Failed to find end of file: {}", file.error_string());
return 1;
}
off_t end = pos;
int lines = 0;
// FIXME: Reading char-by-char is only OK if IODevice'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.data() == '\n' && (end - pos) > 1) {
lines++;
if (lines == wanted_lines)
break;
}
}
}
return pos;
}
int main(int argc, char* argv[])
{
if (pledge("stdio rpath", nullptr) < 0) {
perror("pledge");
return 1;
}
bool follow = false;
int line_count = DEFAULT_LINE_COUNT;
const char* file = nullptr;
Core::ArgsParser args_parser;
args_parser.set_general_help("Print the end ('tail') of a file.");
args_parser.add_option(follow, "Output data as it is written to the file", "follow", 'f');
args_parser.add_option(line_count, "Fetch the specified number of lines", "lines", 'n', "number");
args_parser.add_positional_argument(file, "File path", "file");
args_parser.parse(argc, argv);
auto f = Core::File::construct(file);
if (!f->open(Core::OpenMode::ReadOnly)) {
warnln("Failed to open {}: {}", f->name(), f->error_string());
exit(1);
}
if (pledge("stdio", nullptr) < 0) {
perror("pledge");
return 1;
}
auto pos = find_seek_pos(*f, line_count);
return tail_from_pos(*f, pos, follow);
}
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