Read a file in chunks in Ruby

Question

I need to read a file in MB chunks, is there a cleaner way to do this in Ruby:

FILENAME=\"d:\\\\tmp\\\\file.bin\"
MEGABYTE = 1024*1024
size = File.size(FILEN         


        

Answer 1

Adapted from the Ruby Cookbook page 204:

FILENAME = "d:\\tmp\\file.bin"
MEGABYTE = 1024 * 1024

class File
  def each_chunk(chunk_size = MEGABYTE)
    yield read(chunk_size) until eof?
  end
end

open(FILENAME, "rb") do |f|
  f.each_chunk { |chunk| puts chunk }
end

Disclaimer: I'm a ruby newbie and haven't tested this.

Answer 2

If you check out the ruby docs: http://ruby-doc.org/core-2.2.2/IO.html there's a line that goes like this:

IO.foreach("testfile") {|x| print "GOT ", x }

The only caveat is. Since, this process can read the temp file faster than the generated stream, IMO, a latency should be thrown in.

IO.foreach("/tmp/streamfile") {|line|
  ParseLine.parse(line)
  sleep 0.3 #pause as this process will discontine if it doesn't allow some buffering 
}

Answer 3

Alternatively, if you don't want to monkeypatch File:

until my_file.eof?
  do_something_with( my_file.read( bytes ) )
end

For example, streaming an uploaded tempfile into a new file:

# tempfile is a File instance
File.open( new_file, 'wb' ) do |f|
  # Read in small 65k chunks to limit memory usage
  f.write(tempfile.read(2**16)) until tempfile.eof?
end

Answer 4

FILENAME="d:/tmp/file.bin"

class File
  MEGABYTE = 1024*1024

  def each_chunk(chunk_size=MEGABYTE)
    yield self.read(chunk_size) until self.eof?
  end
end

open(FILENAME, "rb") do |f|
  f.each_chunk {|chunk| puts chunk }
end

It works, mbarkhau. I just moved the constant definition to the File class and added a couple of "self"s for clarity's sake.

Answer 5

You can use IO#each(sep, limit), and set sep to nil or empty string, for example:

chunk_size = 1024
File.open('/path/to/file.txt').each(nil, chunk_size) do |chunk|
  puts chunk
end