Class: File

Inherits:
Object
  • Object
show all
Defined in:
lib/rexec/reverse_io.rb

Overview

Copyright © 2007, 2009, 2011 Samuel G. D. Williams. <www.oriontransfer.co.nz>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Constant Summary collapse

REVERSE_BUFFER_SIZE = 
128

Instance Method Summary collapse

Instance Method Details

#read_reverse(length) ⇒ Object

Read a chunk of data and then move the file pointer backwards.

Calling this function multiple times will return new data and traverse the file backwards.



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# File 'lib/rexec/reverse_io.rb', line 31

def read_reverse(length)
	offset = tell

	if offset == 0
		return nil
	end

	start = [0, offset-length].max

	seek(start, IO::SEEK_SET)

	buf = read(offset-start)

	seek(start, IO::SEEK_SET)

	return buf
end

#reverse_each_line(sep_string = $/, &block) ⇒ Object

Similar to each_line but works in reverse. Don’t forget to call seek_end before you start!



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# File 'lib/rexec/reverse_io.rb', line 80

def reverse_each_line(sep_string=$/, &block)
	line = reverse_gets(sep_string)

	while line != nil
		yield line

		line = reverse_gets(sep_string)
	end
end

#reverse_gets(sep_string = $/) ⇒ Object

This function is very similar to gets but it works in reverse.

You can use it to efficiently read a file line by line backwards.

It returns nil when there are no more lines.



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# File 'lib/rexec/reverse_io.rb', line 56

def reverse_gets(sep_string=$/)
	end_pos = tell

	offset = nil
	buf = ""

	while offset == nil
		chunk = read_reverse(REVERSE_BUFFER_SIZE)
		return (buf == "" ? nil : buf) if chunk == nil

		buf = chunk + buf

		offset = buf.rindex(sep_string)
	end

	line = buf[offset...buf.size].sub(sep_string, "")

	seek((end_pos - buf.size) + offset, IO::SEEK_SET)

	return line
end

#seek_end ⇒ Object

Seek to the end of the file



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# File 'lib/rexec/reverse_io.rb', line 23

def seek_end
	seek(0, IO::SEEK_END)
end