我有一个名为file.txt
这是通过向其添加行来更新的。
我正在通过这段代码阅读它:
$fp = fopen("file.txt", "r");
$data = "";
while(!feof($fp))
{
$data .= fgets($fp, 4096);
}
echo $data;
并且出现大量的线条。
我只想回显文件的最后 5 行
我怎样才能做到这一点 ?
The file.txt
是这样的:
11111111111111
22222222222
33333333333333
44444444444
55555555555555
66666666666
对于大文件,使用 file() 将所有行读入数组有点浪费。以下是读取文件并维护最后 5 行缓冲区的方法:
$lines=array();
$fp = fopen("file.txt", "r");
while(!feof($fp))
{
$line = fgets($fp, 4096);
array_push($lines, $line);
if (count($lines)>5)
array_shift($lines);
}
fclose($fp);
您可以通过寻找一个位置(例如距离末尾大约 10 行)并进一步返回(如果不能产生 5 行),通过一些关于可能的行长度的启发式方法对此进行进一步优化。这是一个简单的实现,它演示了:
//how many lines?
$linecount=5;
//what's a typical line length?
$length=40;
//which file?
$file="test.txt";
//we double the offset factor on each iteration
//if our first guess at the file offset doesn't
//yield $linecount lines
$offset_factor=1;
$bytes=filesize($file);
$fp = fopen($file, "r") or die("Can't open $file");
$complete=false;
while (!$complete)
{
//seek to a position close to end of file
$offset = $linecount * $length * $offset_factor;
fseek($fp, -$offset, SEEK_END);
//we might seek mid-line, so read partial line
//if our offset means we're reading the whole file,
//we don't skip...
if ($offset<$bytes)
fgets($fp);
//read all following lines, store last x
$lines=array();
while(!feof($fp))
{
$line = fgets($fp);
array_push($lines, $line);
if (count($lines)>$linecount)
{
array_shift($lines);
$complete=true;
}
}
//if we read the whole file, we're done, even if we
//don't have enough lines
if ($offset>=$bytes)
$complete=true;
else
$offset_factor*=2; //otherwise let's seek even further back
}
fclose($fp);
var_dump($lines);
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