class File

Public Class Methods

tail(path, n = 1) click to toggle source

@param path [String] - the path to the file @param n [Integer] - the number of lines to read from the path @summary Reads N lines from the end of file, without reading the entire file into memory @return [String] - the data read from the file

# File lib/compute_unit/monkey_patches.rb, line 8
def self.tail(path, n = 1)
  return '' unless File.exist?(path)

  File.open(path, 'r') do |file|
    buffer_s = 512
    line_count = 0
    file.seek(0, IO::SEEK_END)

    offset = file.pos # we start at the end

    while line_count <= n && offset > 0
      to_read = if (offset - buffer_s) < 0
                  offset
                else
                  buffer_s
                end

      file.seek(offset - to_read)
      data = file.read(to_read)

      data.reverse.each_char do |c|
        if line_count > n
          offset += 1
          break
        end
        offset -= 1
        line_count += 1 if c == "\n"
      end
    end
    file.seek(offset)
    file.read
  end
end