Its syntax is: int popen (string command, string mode)
command refers to the system command that will be executed,
mode refers to how you would use the popen() function to search a file:
$fh = fopen("data.txt","w");
fputs($fh, "A\n");
fputs($fh,"B\n");
fputs($fh,"C\n");
fclose($fh);
$fh =popen("grep B < data.txt", "r");
fpassthru($fh);
?>