# Trouble with open/write/close cycle **URL:** \ **Category:** ruby-talk\ **Created:** [24 March 2006 16:43 UTC](https://rubytalk.org/t/trouble-with-open-write-close-cycle/26077 "2006-03-24T16:43:08Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Tobias\_DiPasquale](https://avatars.discourse-cdn.com/v4/letter/t/958977/32.png) [@Tobias\_DiPasquale](https://rubytalk.org/u/Tobias_DiPasquale)\ **Post date:** [24 March 2006 16:43 UTC](https://rubytalk.org/t/trouble-with-open-write-close-cycle/26077/1 "2006-03-24T16:43:08Z")
Hi all, I'm having trouble getting an open/write/close cycle to actually put the correct data in the file. Here's some code that illustrates the problem: \ x = "012345678\n" 10.times do   len = 0   begin     len = File.stat( 'junk').size   rescue     len = 0   end   puts len.to\_s   f = File.open 'crapper', 'w'   f.seek len   f.write x   f.close end \ produces: 0 10 20 30 40 50 60 70 80 90 as output. However, the file 'junk' is filled with zeroes, except for the last 10 bytes, which are what you'd expect them to be: \ puma:~\> od -h junk 0000000 0000 0000 0000 0000 0000 0000 0000 0000 > **···** > > \* > 0000120 0000 0000 0000 0000 0000 3130 3332 3534 > 0000140 3736 0a38 > 0000144 > puma:~\> > \ > > Anyone know what I'm doing wrong? I tried using sysseek and syswrite, > but I got the same results. Is Ruby's internal buffering screwing me up > here somehow? TIA. > > -- > Toby DiPasquale > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Tobias\_DiPasquale](https://avatars.discourse-cdn.com/v4/letter/t/958977/32.png) [@Tobias\_DiPasquale](https://rubytalk.org/u/Tobias_DiPasquale)\ **Post date:** [24 March 2006 16:46 UTC](https://rubytalk.org/t/trouble-with-open-write-close-cycle/26077/2 "2006-03-24T16:46:08Z")
From above: - f = File.open 'crapper', 'w' + f = File.open 'junk', 'w' Sorry. > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Mike\_Stok1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/mike_stok1/32/2065_2.png) [@Mike\_Stok1](https://rubytalk.org/u/Mike_Stok1)\ **Post date:** [24 March 2006 16:57 UTC](https://rubytalk.org/t/trouble-with-open-write-close-cycle/26077/3 "2006-03-24T16:57:47Z")
opening a file for writing truncates it. Does this, opening it for reading & writing, do what you want? x = "012345678\n" 10.times do    len = 0    begin      len = File.stat( 'junk').size    rescue      len = 0    end    puts len.to\_s    f = File.open 'junk',File::RDWR|File::CREAT    f.seek len    f.write x    f.close end Mike > **···** > > On 24-Mar-06, at 11:43 AM, Toby DiPasquale wrote: > > > Hi all, > > > > I'm having trouble getting an open/write/close cycle to actually put the > > correct data in the file. Here's some code that illustrates the problem: > > > > \ > > x = "012345678\n" > > 10.times do > >   len = 0 > >   begin > >     len = File.stat( 'junk').size > >   rescue > >     len = 0 > >   end > >   puts len.to\_s > >   f = File.open 'crapper', 'w' > >   f.seek len > >   f.write x > >   f.close > > end > > \ > > > > produces: > > > > 0 > > 10 > > 20 > > 30 > > 40 > > 50 > > 60 > > 70 > > 80 > > 90 > > > > as output. However, the file 'junk' is filled with zeroes, except for > > the last 10 bytes, which are what you'd expect them to be: > > -- > > Mike Stok \ > [http://www.stok.ca/~mike/](http://www.stok.ca/~mike/) > > The "`Stok' disclaimers" apply. ---
**Author:** ![Chris6](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@Chris6](https://rubytalk.org/u/Chris6)\ **Post date:** [24 March 2006 16:58 UTC](https://rubytalk.org/t/trouble-with-open-write-close-cycle/26077/4 "2006-03-24T16:58:52Z")
> \ >     len = File.stat( 'junk').size > \ >   f = File.open 'crapper', 'w' Are there really 2 files? or is this a typo? The docs on IO::open says tha using the 'w' mode cause the file to be truncated if it exists. You need to look at 'a' mode cheers ---
**Author:** ![James\_Edward\_Gray\_II](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@James\_Edward\_Gray\_II](https://rubytalk.org/u/James_Edward_Gray_II)\ **Post date:** [24 March 2006 17:01 UTC](https://rubytalk.org/t/trouble-with-open-write-close-cycle/26077/5 "2006-03-24T17:01:47Z")
The above procedure seems like a complex way to do: File.open("junk", "a")... Will that work for you? James Edward Gray II > **···** > > On Mar 24, 2006, at 10:43 AM, Toby DiPasquale wrote: > > >   begin > >     len = File.stat( 'junk').size > >   rescue > >     len = 0 > >   end > >   puts len.to\_s > >   f = File.open 'crapper', 'w' > >   f.seek len ---
**Author:** ![Tobias\_DiPasquale](https://avatars.discourse-cdn.com/v4/letter/t/958977/32.png) [@Tobias\_DiPasquale](https://rubytalk.org/u/Tobias_DiPasquale)\ **Post date:** [24 March 2006 17:03 UTC](https://rubytalk.org/t/trouble-with-open-write-close-cycle/26077/6 "2006-03-24T17:03:39Z")
Mike Stok wrote: > opening a file for writing truncates it. ARRRGH! I'm a moron. Of course, you are right. Thanks for the mental clue-by-four. > **···** > > -- > Toby DiPasquale > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Tobias\_DiPasquale](https://avatars.discourse-cdn.com/v4/letter/t/958977/32.png) [@Tobias\_DiPasquale](https://rubytalk.org/u/Tobias_DiPasquale)\ **Post date:** [24 March 2006 17:03 UTC](https://rubytalk.org/t/trouble-with-open-write-close-cycle/26077/7 "2006-03-24T17:03:52Z")
James Gray wrote: > The above procedure seems like a complex way to do: > > File.open("junk", "a")... > > Will that work for you? No, the above code was just a small example to illustrate the issue. The real code does lots more before and after each write. > **···** > > -- > Toby DiPasquale > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Chris6](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@Chris6](https://rubytalk.org/u/Chris6)\ **Post date:** [24 March 2006 17:08 UTC](https://rubytalk.org/t/trouble-with-open-write-close-cycle/26077/8 "2006-03-24T17:08:52Z")
Toby DiPasquale wrote: > From above: > > - f = File.open 'crapper', 'w' > + f = File.open 'junk', 'w' > > Sorry. Not a problem. When I run your snippet i get: > ruby -w fwrite-test.rb 0 11 22 33 44 55 66 77 88 99 It looks like seeking on an empty file fills it with null data. Not sure if thats a Ruby thing or a feature of the underlying IO libs. change the 'w' to an 'a' (an delete the current 'junk' file) and the file produced looks like: 012345678 012345678 012345678 012345678 012345678 012345678 012345678 012345678 012345678 012345678 cheers