This module can be included in your own File subclasses or used to extend files you want to tail.
File::Tail version
If this attribute is set to a true value, File::Fail’s tail method raises a BreakException if the end of the file is reached.
Default buffer size, that is used while going backward from a file’s end. This defaults to nil, which means that File::Tail attempts to derive this value from the filesystem block size.
The start value of the sleep interval. This value goes against max_interval if the tailed file is silent for a sufficient time.
The maximum interval File::Tail sleeps, before it tries to take some action like reading the next few lines or reopening the file.
If this attribute is set to a true value, File::Tail persists on reopening a deleted file waiting max_interval seconds between the attempts. This is useful if logfiles are moved away while rotation occurs but are recreated at the same place after a while. It defaults to true.
If this attribute is set to a true value, File::Tail attempts to reopen it’s tailed file after suspicious_interval seconds of silence.
If this attribute is set to a true value, File::Fail’s tail method just returns if the end of the file is reached.
This attribute is the invterval in seconds before File::Tail gets suspicious that something has happend to it’s tailed file and an attempt to reopen it is made.
If the attribute reopen_suspicious is set to a non true value, suspicious_interval is meaningless. It defaults to 60 seconds.
The callback is called with self as an argument after a reopen has occured. This allows a tailing script to find out, if a logfile has been rotated.
# File lib/file/tail.rb, line 71 def after_reopen(&block) @after_reopen = block end
Rewind the last n lines of this file, starting from the end. The default is to start tailing directly from the end of the file.
The additional argument bufsize is used to determine the buffer size that is used to step through the file backwards. It defaults to the block size of the filesystem this file belongs to or 8192 bytes if this cannot be determined.
# File lib/file/tail.rb, line 117 def backward(n = 0, bufsize = nil) if n <= 0 seek(0, File::SEEK_END) return self end bufsize ||= default_bufsize || stat.blksize || 8192 size = stat.size begin if bufsize < size seek(0, File::SEEK_END) while n > 0 and tell > 0 do start = tell seek(-bufsize, File::SEEK_CUR) buffer = read(bufsize) n -= buffer.count("\n") seek(-bufsize, File::SEEK_CUR) end else rewind buffer = read(size) n -= buffer.count("\n") rewind end rescue Errno::EINVAL size = tell retry end pos = -1 while n < 0 # forward if we are too far back pos = buffer.index("\n", pos + 1) n += 1 end seek(pos + 1, File::SEEK_CUR) self end
Skip the first n lines of this file. The default is to don’t skip any lines at all and start at the beginning of this file.
# File lib/file/tail.rb, line 99 def forward(n = 0) rewind while n > 0 and not eof? readline n -= 1 end self end
This method tails this file and yields to the given block for every new line that is read. If no block is given an array of those lines is returned instead. (In this case it’s better to use a reasonable value for n or set the return_if_eof or break_if_eof attribute to a true value to stop the method call from blocking.)
If the argument n is given, only the next n lines are read and the method call returns. Otherwise this method call doesn’t return, but yields to block for every new line read from this file for ever.
# File lib/file/tail.rb, line 165 def tail(n = nil, &block) # :yields: line @n = n result = [] array_result = false unless block block = lambda { |line| result << line } array_result = true end preset_attributes unless @lines loop do begin restat read_line(&block) redo rescue ReopenException => e until eof? || @n == 0 block.call readline @n -= 1 if @n end reopen_file(e.mode) @after_reopen.call self if @after_reopen rescue ReturnException return array_result ? result : nil end end end
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