From: Joel VanderWerf <vjoel@...>
Date: 2007-06-12T05:03:54+09:00
Subject: Re: Ruby way to update a file in place

Li Chen wrote:
> Hi all,
> 
> I just wonder what is the Ruby way to update a file in place. Do I need
> to open a temporary/new file for writing and then rename the temporary
> file?

You can open with the "r+" file mode, and use seek/rewind to move to a 
position within the file, use #truncate to end the file, and so on.

[~/tmp] cat >foo
foo
bar
baz
[~/tmp] irb
irb(main):001:0> f = File.open("foo", "r+")
=> #<File:foo>
irb(main):002:0> f.puts "FOO"
=> nil
irb(main):003:0> f.seek 8
=> 0
irb(main):004:0> f.puts "BAZ"
=> nil
irb(main):005:0> f.rewind
=> 0
irb(main):006:0> f.read
=> "FOO\nbar\nBAZ\n"
irb(main):007:0> f.close
=> nil
irb(main):008:0> [~/tmp] cat foo
FOO
bar
BAZ

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407