This illustrates reading a line from /etc/passwd

The line: dbus:x:81:81:System message bus:/:/sbin/nologin
A print_r() of the LineReader object:
LineReader Object
(
    [filename:private] => /etc/passwd
    [fp:private] => Resource id #5
    [cache:private] => Array
        (
            [18] => dbus:x:81:81:System message bus:/:/sbin/nologin

        )

    [useCache:private] => 1
)

Caching is normally used unless turned off specifically by passing FALSE as the second argument to the constructor. This means you get a small speed increase when reading from larger files (if you re-read the same line).