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Re: [vox-tech] How to check for data coming in STDIN
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Re: [vox-tech] How to check for data coming in STDIN



On Thu, Jun 21, 2001 at 09:50:02AM -0500, Jay Strauss wrote:
> Actually, I don't get it (well I get it enough to use in my code, but...)
> 
> -t  Filehandle is opened to a tty.
> 
> What does this mean?  I suppose I don't understand what a "tty" is.  I'd
> think "-t" would return a 0 if I wasn't piping something in on STDIN, vs
> returning a 1 when no STDIN

Well, as I mentioned before, there's no such thing as 'no STDIN'
unless you explicitly close it from within the program.  When you
start it without piping, you certainly still have STDIN - the tty.

A tty is actually an archaic abbreviation that isn't really used in
it's original meaning - teletype (I believe - someone correct me
otherwise).  These were 'dumb' terminals that just knew how to accept
and display text, and communicate with a 'smarter' server.  Linux of
course is full of terminals (or more accurately, terminal emulators),
and these are what get called ttys now.  The tty is essentially your
console, xterm, or whatever.

So whenever you invoke a program from the console without specifying a
redirection, your stdin, stdout, and stderr are all connected to that
console, which by definition is a tty.  But pipes and file
redirections are not ttys since they're not the console.  So -t
returns true when STDIN is the console, and false otherwise.

HTH,
Micah


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