# Input redirection in ruby **URL:** \ **Category:** ruby-talk\ **Created:** [31 July 2008 14:10 UTC](https://rubytalk.org/t/input-redirection-in-ruby/48032 "2008-07-31T14:10:10Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Michal\_hramrach\_Such](https://avatars.discourse-cdn.com/v4/letter/m/3ab097/32.png) [@Michal\_hramrach\_Such](https://rubytalk.org/u/Michal_hramrach_Such)\ **Post date:** [31 July 2008 14:10 UTC](https://rubytalk.org/t/input-redirection-in-ruby/48032/1 "2008-07-31T14:10:10Z")
Hello I could not find any way to redirect input and output of programs in ruby. You can capture the fds but not redirect AFAICT. So unless there is something I have overlooked I add the the ruby wishlist: let popen and popen3 take IO arguments for use as stdin, stdout, and stderr. Since they can be named in 1.9 (or was that dropped?) you may specify anything you want. These should probably work only with IO that is backed by a real fd, support for StringIO or similar might be problematic. Thanks Michal ---
**Author:** ![Shadowfirebird](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@Shadowfirebird](https://rubytalk.org/u/Shadowfirebird)\ **Post date:** [31 July 2008 14:27 UTC](https://rubytalk.org/t/input-redirection-in-ruby/48032/2 "2008-07-31T14:27:13Z")
Well, you can say $stderr.puts "message", for example. But I'm guessing that you are talking about something more comprehensive? > **···** > > On Thu, Jul 31, 2008 at 3:10 PM, Michal Suchanek \ wrote: > > > Hello > > > > I could not find any way to redirect input and output of programs in ruby. > > > > You can capture the fds but not redirect AFAICT. > > > > So unless there is something I have overlooked I add the the ruby wishlist: > > > > let popen and popen3 take IO arguments for use as stdin, stdout, and > > stderr. Since they can be named in 1.9 (or was that dropped?) you may > > specify anything you want. These should probably work only with IO > > that is backed by a real fd, support for StringIO or similar might be > > problematic. > > > > Thanks > > > > Michal > > -- > Me, I imagine places that I have never seen / The colored lights in > fountains, blue and green / And I imagine places that I will never go > / Behind these clouds that hang here dark and low > But it's there when I'm holding you / There when I'm sleeping too / > There when there's nothing left of me / Hanging out behind the > burned-out factories / Out of reach but leading me / Into the > beautiful sea ---
**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\ **Post date:** [31 July 2008 17:19 UTC](https://rubytalk.org/t/input-redirection-in-ruby/48032/3 "2008-07-31T17:19:22Z")
You can - and it's pretty easy also. The key feature to know is IO#reopen: robert@fussel ~ $ rm x robert@fussel ~ $ ./ro.rb foo 1 foo 2 robert@fussel ~ $ head x insgesamt 4319 drwx------+ 22 robert Kein 0 Feb 17 16:27 Anwendungsdaten drwx------+ 2 robert Kein 0 Jul 27 23:24 Cookies drwx------+ 12 robert Kein 0 Jul 27 14:18 Desktop drwx------+ 2 robert Kein 0 Aug 18 2004 Druckumgebung drwx------+ 17 robert Kein 0 Apr 20 12:14 Eigene Dateien drwx------+ 5 robert Kein 0 Feb 8 19:58 Favoriten drwx------+ 6 robert Kein 0 Sep 17 2006 Lokale Einstellungen -rwx------+ 1 robert Kein 4194304 Jul 27 12:07 NTUSER.DAT drwx------+ 2 robert Kein 0 Mar 24 18:05 Netzwerkumgebung robert@fussel ~ $ cat ro.rb #!/bin/env ruby puts "foo 1" fork do    STDOUT.reopen("x", "w")    exec "ls", "-l" end puts "foo 2" robert@fussel ~ $ Alternatively you can use the shell's redirection feature when invoking system with one argument only: robert@fussel ~ $ ruby -e 'system "ls -l \> xx"' robert@fussel ~ $ head xx insgesamt 4323 drwx------+ 22 robert Kein 0 Feb 17 16:27 Anwendungsdaten drwx------+ 2 robert Kein 0 Jul 27 23:24 Cookies drwx------+ 12 robert Kein 0 Jul 27 14:18 Desktop drwx------+ 2 robert Kein 0 Aug 18 2004 Druckumgebung drwx------+ 17 robert Kein 0 Apr 20 12:14 Eigene Dateien drwx------+ 5 robert Kein 0 Feb 8 19:58 Favoriten drwx------+ 6 robert Kein 0 Sep 17 2006 Lokale Einstellungen -rwx------+ 1 robert Kein 4194304 Jul 27 12:07 NTUSER.DAT drwx------+ 2 robert Kein 0 Mar 24 18:05 Netzwerkumgebung robert@fussel ~ $ Cheers   robert > **···** > > On 31.07.2008 16:10, Michal Suchanek wrote: > > > I could not find any way to redirect input and output of programs in ruby. > > > > You can capture the fds but not redirect AFAICT. ---
**Author:** ![Michal\_hramrach\_Such](https://avatars.discourse-cdn.com/v4/letter/m/3ab097/32.png) [@Michal\_hramrach\_Such](https://rubytalk.org/u/Michal_hramrach_Such)\ **Post date:** [31 July 2008 23:10 UTC](https://rubytalk.org/t/input-redirection-in-ruby/48032/4 "2008-07-31T23:10:30Z")
Yes, this makes stuff much easier. Still to do what shell does when you use a shell pipe you need a working fork. I am not sure how fork is emulated on platforms that use spawn like Windows. According to porting tutorials passing the fd's is possible with the windows API but doing a full fork() is hard - it normally requires copying the whole address space manually because part of the NT core functionality is not exposed in the Win32 API. Thanks Michal > **···** > > On 31/07/2008, Robert Klemme \ wrote: > > > On 31.07.2008 16:10, Michal Suchanek wrote: > > > > \> I could not find any way to redirect input and output of programs in ruby. > > \> > > \> You can capture the fds but not redirect AFAICT. > > \> > > > > You can - and it's pretty easy also. The key feature to know is IO#reopen: ---
**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\ **Post date:** [1 August 2008 06:47 UTC](https://rubytalk.org/t/input-redirection-in-ruby/48032/5 "2008-08-01T06:47:24Z")
Well, I was actually on Windows (although I have to admit that I use the cygwin version all the time). 🙂 Can't remember: do IO.popen and friends work in the Windows version? If it does, then you got your redirection with pipes already. Kind regards robert > **···** > > 2008/8/1 Michal Suchanek \: > > > On 31/07/2008, Robert Klemme \ wrote: > > > > > On 31.07.2008 16:10, Michal Suchanek wrote: > > > > > > \> I could not find any way to redirect input and output of programs in ruby. > > > \> > > > \> You can capture the fds but not redirect AFAICT. > > > \> > > > > > > You can - and it's pretty easy also. The key feature to know is IO#reopen: > > > > Yes, this makes stuff much easier. Still to do what shell does when > > you use a shell pipe you need a working fork. I am not sure how fork > > is emulated on platforms that use spawn like Windows. > > -- > use.inject do |as, often| as.you\_can - without end