Neat Ruby Tricks: File.open Return Values

Published 17 November 2009 by Farrel

Back when I started using Ruby I would often read in data from a file as follows

1 file = File.new( 'data.txt' )
2 parsed_data = parse( file )
3 file.close

Later I switched to using File.open which handles closing the file for you

1 parsed_data = nil # Required otherwise parsed_data will be nil outside the block
2 File.open( 'data.txt' ) do |file|
3   parsed_data = parse( file )
4 end

Recently I realised, and felt pretty stupid for not having realised it earlier, that File.open will return the last expression evaluated in it’s block. Which means the above can be rewritten as

1 parsed_data = File.open( 'data.txt' ) do |file|
2   parse( file )
3 end

or as a much more elegent single line version (and now my preferred method)

1 parsed_data = File.open( 'data.txt' ){ |file| parse( file )}

Farrel Lifson is a lead developer at Aimred.