loop through text file

[bookbuyer2000]

I've seen this question asked before, with different answers. I'm curious which is the most "efficient" (fastest, lowest overhead, etc.) way for php to do the following:

Find all numbers in a large textfile that begins with the three-digit-sequence "658" and replace those numbers by itself mulitplied by 2.

A sample of my textfile might look like:

"577563","green","apple","658377"
"38821","blue","banana","658820"
"599382","yellow","grape","6588993"

In that example, there are 3 numbers that begin with "658":
658377, 658820, and 6588993

I want those 3 numbers replaced with 1316754, 1317640 13177986

My textfile is extremely large, hence my need for the "most efficient" way for php to do this.

Thank you! 🙂

[bradgrafelman]

One solution that uses more memory:

$data = file_get_contents('file.txt');
$data = preg_replace('/"(658\d*)"/e', '"($1 * 2)"', $data);
file_put_contents('file.txt', $data);

[Installer]

This should use less memory and for large files may not be much slower if at all:

$find = '658';
$fpr = fopen($file, 'r');
$fpw = fopen($new_file, 'w');
while ($line = fgetcsv($fpr)) {
    foreach ($line as & $each) {
        if (strpos($each, $find) === 0) {
            $each *= 2;
        }
    }
    fputcsv($fpw, $line);
}
fclose($fpr);
fclose($fpw);

But it does consume more editor space.