From: ara.t.howard@...
Date: 2006-09-28T06:50:03+09:00
Subject: Re: how to determine if pipe is given

On Thu, 28 Sep 2006 gwtmp01@mac.com wrote:

> If your program is prepared to deal with piped input, why are you concerned
> about input coming from the keyboard?  If I found a program that worked as:
>
> 	cat file | program
>
> and as
>
> 	program < file
>
> but did not work as just
>
> 	program

it may well work, but hang forever in cron though:

this is as easy to do as

   infile = get_infile          # oops, returned nil
   system "program #{ infile }" # hangs forever

that's also very problematic for prorgams which take two arguments:

   cat infile | program - outfile
   cat infile | program - - | outfile_filter > outfile

note that you cannot simply say that the abscence of infile means stdin and
similar for outfile because

   program infile_or_outfile?

i'm sure one could skin this differently, i just have debugged many hung
processes that make assumptions based on STDIN.tty?

kind regards.

-a
-- 
in order to be effective truth must penetrate like an arrow - and that is
likely to hurt. -- wei wu wei