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#!/usr/bin/env python
"""
Clone of the standard UNIX "tail" command.
This example shows how you can utilize some of the buitlin I/O components
in circuits to write a very simple clone of the standard UNIX "tail" command.
"""
import sys
from circuits import Component, Debugger
from circuits.io import File, Write, stdout
class Tail(Component):
# Shorthand for declaring a compoent to be a part of this component.
stdout = stdout
def init(self, filename):
"""
Initialize Tail Component
Using the convenience ``init`` method we simply register a ``File``
Component as part of our ``Tail`` Component and ask it to seek to
the end of the file.
"""
File(filename, 'r', autoclose=False).register(self).seek(0, 2)
def read(self, data):
"""
Read Event Handler
This event is triggered by the underlying ``File`` Component for
when there is data to be processed. Here we simply fire a ``Write``
event and target the ``stdout`` component instance that is a part of
our system -- thus writing the contents of the file we read out
to standard output.
"""
self.fire(Write(data), self.stdout)
# Setup and run the system.
(Tail(sys.argv[1]) + Debugger()).run()
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