# Std. IO streams in Ruby **URL:** \ **Category:** Rails\ **Created:** [August 1, 2010, 8:29pm UTC](https://www.ruby-forum.com/t/std-io-streams-in-ruby/197143 "2010-08-01T20:29:57Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![silver-spoon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aeb1de/32.png) [@silver-spoon](https://www.ruby-forum.com/u/silver-spoon)\ **Post date:** [August 1, 2010, 8:29pm UTC](https://www.ruby-forum.com/t/std-io-streams-in-ruby/197143/1 "2010-08-01T20:29:57Z")
In my rails controller, I am doing the following : @output = `g++ j.cpp -o "prog" && ./prog` This gives the output in the @output variable which i can display in my view. But the above works only if the j.cpp is correct and doesn’t expect any user input. How can I use the stdin/stderr and stdout streams here so that : If the user has to give input, I open a dialog box on the view with a textfield where he/she can enter the input, and the program continues to execute. If there are any errors in the file, then I should be able to get the errors and display them to the user. I tried doing this : @output = `g++ j.cpp -o "prog" && ./prog| tee prog` This allows me to enter the user input at the server command prompt (the server log…i don’t know what do we call it), but I want it to be entered in a textfield in the view. In short, how can I get control of stdin, so that whenever the stdin waits for some user input, i get to know that it is waiting for the user input and then i can show the user a text field and get the user input to be passed in the stdin stream. Let me know if there’s a doubt in the question. ---
**Author:** ![silver-spoon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aeb1de/32.png) [@silver-spoon](https://www.ruby-forum.com/u/silver-spoon)\ **Post date:** [August 1, 2010, 9:32pm UTC](https://www.ruby-forum.com/t/std-io-streams-in-ruby/197143/2 "2010-08-01T21:32:02Z")
On Aug 1, 7:29 pm, Jatin K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > textfield where he/she can enter the input, and the program continues to > > In short, how can I get control of stdin, so that whenever the stdin > waits for some user input, i get to know that it is waiting for the user > input and then i can show the user a text field and get the user input > to be passed in the stdin stream. > Let me know if there’s a doubt in the question. Well in a plain old ruby script IO.popen allows you to run a command and gets you the command stdin/stdout (and open3/popen3 gets you stderr too). Controlling this interactively via a webapp is much more tricky. A single http request only has a single response, so you’d have to break this up across multiple requests. There’s no guarantee that the next request from the user will go to the same rails instance, so figuring out what do do with the IO objects connecting you to the command being run is tricky enough. One possible way out is to have some long running daemon process that does that actual running of the command and have your rails actions communicate with that. If just polling for whether the command is waiting for input isn’t acceptable then you might need to look at comet and that sort of thing. If you can restrict yourself to specific browsers, the new html5 websockets stuff might be interesting too Fred ---
**Author:** ![silver-spoon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aeb1de/32.png) [@silver-spoon](https://www.ruby-forum.com/u/silver-spoon)\ **Post date:** [August 1, 2010, 10:09pm UTC](https://www.ruby-forum.com/t/std-io-streams-in-ruby/197143/3 "2010-08-01T22:09:37Z")
Frederick C. wrote: > On Aug 1, 7:29�pm, Jatin K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > textfield where he/she can enter the input, and the program continues to > > > > In short, how can I get control of stdin, so that whenever the stdin > > waits for some user input, i get to know that it is waiting for the user > > input and then i can show the user a text field and get the user input > > to be passed in the stdin stream. > > Let me know if there’s a doubt in the question. > > Well in a plain old ruby script IO.popen allows you to run a command > and gets you the command stdin/stdout (and open3/popen3 gets you > stderr too). > > Controlling this interactively via a webapp is much more tricky. A > single http request only has a single response, so you’d have to break > this up across multiple requests. There’s no guarantee that the next > request from the user will go to the same rails instance, so figuring > out what do do with the IO objects connecting you to the command being > run is tricky enough. > > One possible way out is to have some long running daemon process that > does that actual running of the command and have your rails actions > communicate with that. If just polling for whether the command is > waiting for input isn’t acceptable then you might need to look at > comet and that sort of thing. If you can restrict yourself to specific > browsers, the new html5 websockets stuff might be interesting too > > Fred @Fred :-I have been looking over the internet for a solution but never got a real answer. Thanks for your help. My web app allows the user to run code in the browser window itself, so do i really need to do polling for that? I mean is there any better solution? If not, how can I use your approach. I have never tried something like that before, so a little confused. Can you explain it using a little code snippet? That would really help me out. Also, the responses would be through AJAX. The user code will be sent back to server through an AJAX call, the file created for the code and then the response back to the browser(the output of file executed) in an AJAX call. So, that guarantee that next request will go to same rails instance, won’t that vanish away or not? Could be elaborate a little bit on this too. ---
**Author:** ![silver-spoon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aeb1de/32.png) [@silver-spoon](https://www.ruby-forum.com/u/silver-spoon)\ **Post date:** [August 2, 2010, 1:34am UTC](https://www.ruby-forum.com/t/std-io-streams-in-ruby/197143/4 "2010-08-02T01:34:22Z")
On Aug 1, 9:09 pm, Jatin K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > something like that before, so a little confused. Can you explain it > using a little code snippet? That would really help me out. Don’t have any code snippets, just one way I’d try tackling this - run the commands from a separate ruby process and use whatever mechanism you want (drb might be handy) to allow your controller action to get from this process what the state of the command being run is. > Also, the responses would be through AJAX. The user code will be sent > back to server through an AJAX call, the file created for the code and > then the response back to the browser(the output of file executed) in an > AJAX call. So, that guarantee that next request will go to same rails > instance, won’t that vanish away or not? Could be elaborate a little bit > on this too. Unless I’ve misunderstood your command needs to keep running over the course of several requests if you’re going to be getting input from the users at the point. Unless you’re willing for your rails code to just block until input is required ( not a great idea) you’ll need some form of polling/comet.