PHP is a server-side language and one of the handy things it provides is access to the filesystem.

You can check if a file exists using file_exists():

file_exists('test.txt') //true

Get the size of a file using filesize():

filesize('test.txt')

You can open a file using fopen(). Here we open the test.txt file in read-only mode and we get what we call a file descriptor in $file:

$file = fopen('test.txt', 'r')

We can terminate the file access calling fclose($fd).

Read the content of a file into a variable:

$file = fopen('test.txt', 'r')

fread($file, filesize('test.txt'));

//or

while (!feof($file)) {
	$data .= fgets($file, 5000);
}

feof() checks that we haven’t reached the end of the file as fgets reads 5000 bytes at a time

You can also read a file line by line using fgets():

$file = fopen('test.txt', 'r')

while(!feof($file)) {
  $line = fgets($file);
  //do something
}

To write to a file you must first open it in write mode, then use fwrite():

$data = 'test';
$file = fopen('test.txt', 'w')
fwrite($file, $data);
fclose($file);

We can delete a file using unlink():

unlink('test.txt')

Those are the basics, of course there are more functions to work with files.