# How to catch STDIO STREAM? **URL:** \ **Category:** Ruby\ **Created:** [May 26, 2008, 11:53pm UTC](https://www.ruby-forum.com/t/how-to-catch-stdio-stream/138699 "2008-05-26T23:53:36Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![cheyne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b9bd4f/32.png) [@cheyne](https://www.ruby-forum.com/u/cheyne)\ **Post date:** [May 26, 2008, 11:53pm UTC](https://www.ruby-forum.com/t/how-to-catch-stdio-stream/138699/1 "2008-05-26T23:53:36Z")
Hi, there How can I capture a error massage from the STD IO? For instance, I have a program call foo.exe and i run the program ./foo.exe Then the program prints out some error messages. How can I write a script that capture the errors and save then into a file? ---
**Author:** ![cheyne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b9bd4f/32.png) [@cheyne](https://www.ruby-forum.com/u/cheyne)\ **Post date:** [May 26, 2008, 11:59pm UTC](https://www.ruby-forum.com/t/how-to-catch-stdio-stream/138699/2 "2008-05-26T23:59:46Z")
-------- Original-Nachricht -------- > Datum: Tue, 27 May 2008 06:52:55 +0900 > Von: Cheyne Li [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > An: removed\_email\_address@domain.invalid > Betreff: How to catch STDIO STREAM? > – > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). Dear Cheyne, have a look at this: [http://www.ruby-doc.org/stdlib/libdoc/open3/rdoc/index.html](http://www.ruby-doc.org/stdlib/libdoc/open3/rdoc/index.html) Best regards, Axel ---
**Author:** ![cheyne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b9bd4f/32.png) [@cheyne](https://www.ruby-forum.com/u/cheyne)\ **Post date:** [May 27, 2008, 12:39am UTC](https://www.ruby-forum.com/t/how-to-catch-stdio-stream/138699/3 "2008-05-27T00:39:40Z")
-------- Original-Nachricht -------- > Datum: Tue, 27 May 2008 07:21:55 +0900 > Von: Cheyne Li [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > An: removed\_email\_address@domain.invalid > Betreff: Re: How to catch STDIO STREAM? > Thank you for your information. I tried, but it only give me result like > #IO:0xf60e8 > > So, is there a way to convert it into string? Dear Cheyne, yes, there is. Use readlines, like this: * * * require “open3” filenames=%w[file1 file2 file3] inp,out,err=Open3.popen3(“xargs”,“ls”,“-l”) filenames.each{|f| inp.puts f} inp.close output=out.readlines errout=err.readlines ## puts “sent #{filenames.size} lines of input” puts “got back #{output.size} lines of output” puts “these were the errors, if any:” puts errout Best regards, Axel ---
**Author:** ![cheyne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b9bd4f/32.png) [@cheyne](https://www.ruby-forum.com/u/cheyne)\ **Post date:** [May 27, 2008, 8:45am UTC](https://www.ruby-forum.com/t/how-to-catch-stdio-stream/138699/4 "2008-05-27T08:45:39Z")
On 26.05.2008 23:52, Cheyne Li wrote: > How can I capture a error massage from the STD IO? > For instance, I have a program call foo.exe and i run the program > /foo.exe > > Then the program prints out some error messages. > > How can I write a script that capture the errors and save then into a > file? You do not need Ruby for that. At an arbitrary shell prompt: foo.exe \> errors.txt Kind regards robert ---
**Author:** ![cheyne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b9bd4f/32.png) [@cheyne](https://www.ruby-forum.com/u/cheyne)\ **Post date:** [May 27, 2008, 12:22am UTC](https://www.ruby-forum.com/t/how-to-catch-stdio-stream/138699/5 "2008-05-27T00:22:24Z")
Thank you for your information. I tried, but it only give me result like #IO:0xf60e8 So, is there a way to convert it into string? Axel E. wrote: > -------- Original-Nachricht -------- > > > Datum: Tue, 27 May 2008 06:52:55 +0900 > > Von: Cheyne Li [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > > An: removed\_email\_address@domain.invalid > > Betreff: How to catch STDIO STREAM? > > > – > > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). > > Dear Cheyne, > > have a look at this: > > [http://www.ruby-doc.org/stdlib/libdoc/open3/rdoc/index.html](http://www.ruby-doc.org/stdlib/libdoc/open3/rdoc/index.html) > > Best regards, > > Axel ---
**Author:** ![cheyne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b9bd4f/32.png) [@cheyne](https://www.ruby-forum.com/u/cheyne)\ **Post date:** [May 27, 2008, 4:25pm UTC](https://www.ruby-forum.com/t/how-to-catch-stdio-stream/138699/6 "2008-05-27T16:25:07Z")
Robert K. wrote: > foo.exe \> errors.txt I’m sorry, I don’t know Windows that well, but wouldn’t that redirect stdout and not stderr? Or maybe it would redirect both, but what I think the OP wants is to just redirect the errors while still printing the normal messages to the screen. ---
**Author:** ![cheyne](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b9bd4f/32.png) [@cheyne](https://www.ruby-forum.com/u/cheyne)\ **Post date:** [May 27, 2008, 5:45pm UTC](https://www.ruby-forum.com/t/how-to-catch-stdio-stream/138699/7 "2008-05-27T17:45:35Z")
On 27.05.2008 16:23, Sebastian H. wrote: > Robert K. wrote: > > > foo.exe \> errors.txt > > I’m sorry, I don’t know Windows that well, but wouldn’t that redirect stdout > and not stderr? Correct. > Or maybe it would redirect both, but what I think the OP > wants is to just redirect the errors while still printing the normal messages > to the screen. He did not mention explicitly which stream he wanted to redirect that’s why I presented this solution. Of course, you can as well redirect stderr on Windows. Kind regards robert