Read a file from line X to line Y ?

Question

Hello,

Is there a way to read a file in PHP5 from line X to line Y into a string, without reading the entire file.

I would like to return huge files (10,000+ lines) using ajax requests. Each request will provide the client with additional lines. And due to the fact that the file can reach large sizes, I would like to avoid reading it whole over and over again.

Thank you.

Answer 1

Here is the possible solution :)

<?php
$f = fopen('sample.txt', 'r');
$lineNo = 0;
$startLine = 3;
$endLine = 6;
while ($line = fgets($f)) {
    $lineNo++;
    if ($lineNo >= $startLine) {
        echo $line;
    }
    if ($lineNo == $endLine) {
        break;
    }
}
fclose($f);
?>

Answer 2

Well, you can't use function fseek to seek the appropriate position because it works with given number of bytes.

I think that it's not possible without some sort of cache or going through lines one after the other.

Answer 3

I was afraid of that... I guess it's plan B then :S

For each AJAX request I'm going to:

1. Read into a string the number of lines I'm going to return to the client.
2. Copy the rest of the file into a temp file.
3. Return string to the client.

It's lame, and it will probably be pretty slow with 10,000+ lines files, but I guess it's better than reading the same over and over again, at least the temp file is getting shorter with every request... No?

Answer 4

Yes, you can do that easily with SplFileObject::seek

$file = new SplFileObject('filename.txt');
$file->seek(1000);
for($i = 0; !$file->eof() && $i < 1000; $i++) {
    echo $file->current(); 
    $file->next();
}

This is a method from the SeekableIterator interface and not to be confused with fseek.

And because SplFileObject is iterable you can do it even easier with a LimitIterator:

$file = new SplFileObject('longFile.txt');
$fileIterator = new LimitIterator($file, 1000, 2000);
foreach($fileIterator as $line) {
    echo $line, PHP_EOL;
}

Again, this is zero-based, so it's line 1001 to 2001.