From: Randy Kramer <rhkramer@...>
Date: 2007-10-27T03:08:02+09:00
Subject: Nested blocks

Recently I've written several small utilities which are basically 
filters--they read a file one line at a time, do something with one or more 
of those lines, and write one or more lines to an output file.

(With help at various times from the list) I got those utilities working with 
a nested block structure something like this:

File.open("output file", "w") do |f| 
   File.open("input file").each do |line| 
      do stuff
   end
end

For the next somewhat similar utility, that won't work as well--I really want 
to nest the blocks the other way (at least I think so ;-).

The difference (in required functionality) is that this time I need to split 
the single input file into multiple output files (multiple entire records (of 
varying size) not exceeding a specified maximum file size).

I can see how to do it something like this (beware the pseudo-code / 
handwaving):

output_file_size = 0
f = File.open("output file")
File.for each("input_file", rec_sep) do |record| 
   if output_file_size + record.length <= max_file_size then 
      puts f.record
      output_file_size = output_file_size + record.length
   else
      f.close
      construct next output file name
      output_file_size = 0
      f = File.open(next output file) 
   end
f.close
end

But I wonder if there is a way to do it with a block for the output file. 

(ignoring an approach using something like the following to write each record:

File.open("output file").each { |f| f.puts record}

which opens and closes each output file multiple times, once for each record 
written.
)

More specifically, I'm wondering if there is a way to make something like this 
work:

create output file name (-1--i.e., one less than desired file name)
File.for each("input file", rec_sep) do |record| 
increment output file name #pretty sure this is not in the right place
   File.open("output file").each do |f| 
      if output_file_size >= max_file_size then break end
      puts f.record
   end
end

Randy Kramer