Class: File

Inherits:
Object
  • Object
show all
Defined in:
lib/rsgrep/file.rb

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.sgrep(key, filename, options = {}) ⇒ Object 



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# File 'lib/rsgrep/file.rb', line 2

def self.sgrep key, filename, options = {}
  File.open(filename) do |f|
    f.sgrep key, options
  end
end

Instance Method Details

#sgrep(key, options = {}) ⇒ Object 



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# File 'lib/rsgrep/file.rb', line 8

def sgrep key, options = {}
  # initialise the variables that the binary search algorithm needs.
  hi  = size
  lo  = 0
  mid = (hi + lo) / 2
  ret = []

  if options[:insensitive]
    comparator = Proc.new do |key, line|
      key  = key.downcase
      line = line.downcase
      if line.start_with? key
        0
      else
        key <=> line
      end
    end
  else
    comparator = Proc.new do |key, line|
      if line.start_with? key
        0
      else
        key <=> line
      end
    end
  end

  while lo < mid and mid < hi
    seek(mid)
    seek(-2, IO::SEEK_CUR) while (c = getc) != "\n" and c != nil

    case comparator.call(key, (line = gets))
    when 0
      # So we've found a line that matches the key, but this may not be the
      # first line that does (due to the nature of binary searching). This
      # begin/end block scans backwards in the file to find the first line
      # that matches the key.
      begin
        # Seek back 2 lines because "gets" will advance the file pointer
        # forward.
        2.times do
          seek(-2, IO::SEEK_CUR) # First read will always be a newline, skip it
          seek(-2, IO::SEEK_CUR) while (c = getc) != "\n" and c != nil
        end
      end while comparator.call(key, (line = gets)) == 0

      # Then scan forward line by line until all of the lines that match have
      # been added to the return array.
      ret << line.rstrip while (line = gets) != nil and comparator.call(key, line) == 0

      # and we're done!
      return ret
    when -1
      # Key is less than the line. Shift the hi value down and recalculate the
      # mid.
      hi = mid
      mid = (hi + lo) / 2
    when 1
      # Key is greater than the line. Shift the lo value up and recalculate
      # the mid.
      lo = mid
      mid = (hi + lo) / 2
    else
      raise "Should not be raised, ever."
    end
  end

  return ret
end