Question

I would like to cut off the beginning of a large file in PHP. Use of file_get_contents() is not possible due to memory restrictions.

What is the best way to delete the first $n characters from a file?

If it is possible to do it without creating a second file, I would prefer that solution.

Update After the file has been modified, it will be used by other scripts.

Answer 1

If you don’t have enough memory to buffer the entire file, you’ll need to create two files (at least temporarily) regardless of your solution.

Look into fseek(), which allows you to go to a particular byte position within a file.

// Open the file
$filename = 'somefile.dat';
$file = fopen($filename, 'r');

// Skip the first 1 KB
fseek($file, 1024);

// Your processing goes here...

// Close the file
fclose($file);

In your case, you could open the original file for reading and the temp file for writing concurrently. Seek the original file. Loop over the original file, reading a small chunk and writing it to temp. Then rename temp to have the same name as original.