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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



Thanks,

that works.

Jay
----- Original Message ----- 
From: "Micah Cowan" <micah@cowanbox.com>
To: <vox-tech@franz.mother.com>
Sent: Wednesday, June 20, 2001 6:30 PM
Subject: Re: [vox-tech] How to check for data coming in STDIN


> On Wed, Jun 20, 2001 at 06:06:39PM -0500, Jay Strauss wrote:
> > In perl, if I have a pgm:
> > 
> > while (<>) {
> >     print "this is the line: $_";
> > }
> > 
> > normally I'd invoke the pgm like:
> > 
> > echo "repeat this line" | ./pgm
> > 
> > But if I accidentally invoke it like:
> > 
> > ./pgm 
> > 
> > How would I prevent the while loop from running (i.e. pseudocode):
> > 
> > while (<>) if (exists <STDIN>) {
> >     print "$_";
> > }
> 
> Well, that won't work - and the while (<>) actually does that for you
> automatically anyway.
> 
> It won't work though because STDIN /does/ exist.  It's the interactive
> tty by default (when it's not getting a redirected input).
> 
> You can exploit /that/ fact, though, by doing this (tested):
> 
> -------
> #!/usr/bin/perl -w
> 
> die "Hey!  I was expecting a redirected STDIN!\n" if (-t);
> print "this is the line: $_" while (<>);
> -------
> 
> The -t test evaluates to true if it's argument is a tty - if no arg is
> given, STDIN is assumed.
> 
> Micah


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