From: Robert Klemme <shortcutter@...>
Date: 2007-12-24T04:49:59+09:00
Subject: Re: Fairly elementary UNIX question

On 23.12.2007 19:57, Ken Bloom wrote:
> Steckly, Ron <rsteckly@wharton.upenn.edu> wrote:
>> I've been learning a lot about the .NET architecture and scripting to it
>> using Visual Basic and C#.  I'm trying to write a program right now in
>> UNIX and I'm a little perplexed.  How do I tap into events in UNIX?  For
>> example, if I were to write a script to enter a command into the R
>> Statistics Program running in Linux, how would I do that? 
>>
>> Normally, in bash I would type R
>>
>> And a new prompt comes up and you can type whatever command you want.
>>
>> I'd like to be able to make a simple GUi for it so that its easier for
>> people to enter commands who are still learning R.  But I'm not sure how
>> to script to a terminal....
>>
>> Am I completely on the wrong track?
> 
> On UNIX, terminal programs simply have a few open pipes (which behave
> like files) by default, the standard input, standard output, and
> standard error. When you start a new program, the calling program is
> given the other end of each of those pipes. (It's a little more
> complicated, but various ruby libraries abstract away the compliation
> and make this process appear exactly as I said it.) When a program
> runs in a terminal on UNIX, the terminal is the calling process. All
> the terinal does is display the data that's written to stdout and
> stderr, and takes keyboard input and sends it to stdin.  When
> Ruby calls a program, Ruby is the calling process, and you can use the
> pipes however you want. You can get access to the pipes by using popen
> (built-in) or the Open3 or Open4 libraries.
> 
> Note that if you want the output of R to appear on Ruby's calling
> terminal, you have to do a little work to put the output there
> yourself.

Sorry to nitpick, but if you start a program from the shell without a 
pipeline and any redirections , stdout, stderr and stdin are not 
connected to pipes but to devices of the terminal.  (This is also true 
for the shell's own file descriptors 0, 1 and 2.)

Kind regards

	robert