113 lines
3.2 KiB
Python
113 lines
3.2 KiB
Python
#!/usr/bin/env python
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"""Python-Tail - Unix tail follow implementation in Python.
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python-tail can be used to monitor changes to a file.
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Example
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-------
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>>> import tail
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>>>
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>>> # Create a tail instance
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>>> t = tail.Tail('file-to-be-followed')
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>>>
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>>> # Register a callback function to be called when a new line is found in the followed file.
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>>> # If no callback function is registerd, new lines would be printed to standard out.
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>>> t.register_callback(callback_function)
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>>>
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>>> # Follow the file with 5 seconds as sleep time between iterations.
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>>> # If sleep time is not provided 1 second is used as the default time.
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>>> t.follow(s=5)
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"""
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# Author - Kasun Herath <kasunh01 at gmail.com>
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# Source - https://github.com/kasun/python-tail
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# modified by Hans-Christoph Steiner <hans@eds.org> to add the
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# background thread and support reading multiple lines per read cycle
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import os
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import sys
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import time
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import threading
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class Tail(object):
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"""Represents a tail command."""
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def __init__(self, tailed_file):
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"""Initialize a Tail instance.
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Check for file validity, assigns callback function to standard out.
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Parameters
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----------
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tailed_file
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File to be followed.
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"""
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self.check_file_validity(tailed_file)
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self.tailed_file = tailed_file
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self.callback = sys.stdout.write
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self.t_stop = threading.Event()
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def start(self, s=1):
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"""Start tailing a file in a background thread.
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Parameters
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----------
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s
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Number of seconds to wait between each iteration; Defaults to 3.
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"""
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t = threading.Thread(target=self.follow, args=(s,))
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t.start()
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def stop(self):
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"""Stop a background tail."""
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self.t_stop.set()
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def follow(self, s=1):
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"""Do a tail follow.
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If a callback function is registered it is called with every new line.
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Else printed to standard out.
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Parameters
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----------
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s
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Number of seconds to wait between each iteration; Defaults to 1.
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"""
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with open(self.tailed_file) as file_:
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# Go to the end of file
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file_.seek(0, 2)
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while not self.t_stop.is_set():
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curr_position = file_.tell()
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lines = file_.readlines()
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if len(lines) == 0:
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file_.seek(curr_position)
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else:
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for line in lines:
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self.callback(line)
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time.sleep(s)
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def register_callback(self, func):
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"""Override default callback function to provided function."""
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self.callback = func
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def check_file_validity(self, file_):
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"""Check whether the a given file exists, readable and is a file."""
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if not os.access(file_, os.F_OK):
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raise TailError("File '%s' does not exist" % (file_))
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if not os.access(file_, os.R_OK):
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raise TailError("File '%s' not readable" % (file_))
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if os.path.isdir(file_):
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raise TailError("File '%s' is a directory" % (file_))
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class TailError(Exception):
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def __init__(self, msg):
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super().__init__()
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self.message = msg
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def __str__(self):
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return self.message
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