Class: File

Inherits:
Object show all
Defined in:
lib/epitools/core_ext/file.rb

Instance Method Summary collapse

Instance Method Details

#reverse_each(&block) ⇒ Object

A streaming reverse_each implementation. (For large files, it’s faster and uses less memory.)



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# File 'lib/epitools/core_ext/file.rb', line 13

def reverse_each(&block)
  return to_enum(:reverse_each) unless block_given?

  seek_end
  reverse_each_from_current_pos(&block)
end

#reverse_each_from_current_pos {|fragment| ... } ⇒ Object

Read each line of file backwards (from the current position.)

Yields:

  • (fragment) 


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# File 'lib/epitools/core_ext/file.rb', line 54

def reverse_each_from_current_pos
  return to_enum(:reverse_each_from_current_pos) unless block_given?

  # read the rest of the current line, in case we started in the middle of a line
  start_pos = pos
  fragment = readline rescue ""
  seek(start_pos)

  while data = reverse_read(4096)
    lines = data.each_line.to_a
    lines.last << fragment unless lines.last[-1] == "\n"

    fragment = lines.first

    lines[1..-1].reverse_each { |line| yield line }
  end

  yield fragment
end

#reverse_read(length, block_aligned = false) ⇒ Object

Read the previous length bytes. After the read, pos will be at the beginning of the region that you just read. Returns nil when the beginning of the file is reached.

If the block_aligned argument is true, reads will always be aligned to file positions which are multiples of 512 bytes. (This should increase performance slightly.)



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# File 'lib/epitools/core_ext/file.rb', line 27

def reverse_read(length, block_aligned=false)
  raise "length must be a multiple of 512" if block_aligned and length % 512 != 0

  end_pos = pos
  return nil if end_pos == 0

  if block_aligned
    misalignment = end_pos % length
    length      += misalignment
  end

  if length >= end_pos # this read will take us to the beginning of the file
    seek(0)
  else
    seek(-length, IO::SEEK_CUR)
  end

  start_pos = pos
  data      = read(end_pos - start_pos)
  seek(start_pos)

  data
end

#reverse_readline ⇒ Object

Read the previous line (leaving pos at the beginning of the string that was read.)

Raises:



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# File 'lib/epitools/core_ext/file.rb', line 91

def reverse_readline
  raise BOFError.new("beginning of file reached") if pos == 0

  seek_backwards_to("\n", 512, -2)
  new_pos = pos
  data = readline
  seek(new_pos)
  data
end

#seek_backwards_to(string, blocksize = 512, rindex_end = -1)) ⇒ Object

Scan backwards in the file until string is found, and set the IO’s pos to the first character after the matched string.



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# File 'lib/epitools/core_ext/file.rb', line 104

def seek_backwards_to(string, blocksize=512, rindex_end=-1)
  loop do
    data = reverse_read(blocksize)

    if index = data.rindex(string, rindex_end)
      seek(index+string.size, IO::SEEK_CUR)
      break
    elsif pos == 0
      break
    end
  end
end

#seek_end ⇒ Object

Seek to EOF



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# File 'lib/epitools/core_ext/file.rb', line 77

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

#seek_start ⇒ Object

Seek to BOF



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# File 'lib/epitools/core_ext/file.rb', line 84

def seek_start
  seek(0)
end