Check file

<?php/*********************************************************//* File verification and input                           *//* Stelcheck                                             *//*********************************************************/print "Checking input... ";  $usr = str_replace(" ", "", $_GET['user']);  if($usr == ""){    echo 'Error : User name is empty!';    exit;  }print "Done<br />";print "Opening user file... ";$user = fopen("username.txt", "r+") or die("Unable to open file!");if ($user){    print "Done<br />";    print "Verifying user identity... ";    while (!feof($user)) {        $buffer = str_replace(" ", "", fgets($user, 4096));        if($buffer == $_GET['user'].""){          echo 'Error : User name already exist!';          fclose($user);          exit;        }    }    print "Done<br />";    print "Inserting user...";    $userString = "\r\n".$usr;    if (fwrite($user, $userString) === FALSE) {        echo "Cannot write to file username.txt";        exit;    }    print "Done!<br />";    fclose($user);}?>