From: Ara.T.Howard@...
Date: 2004-10-16T11:24:28+09:00
Subject: Re: Popen and operations failing later

On Sat, 16 Oct 2004, David G. Andersen wrote:

> This is likely my brain missing something, but I'm having a hard
> time figuring out the source of this error.  I have code that
> does:
>
> class foo
>
>  def get_next_line
>    if the file isn't open
>       @file = popen("zcat <file>")
>    end
>    begin
>     line = @file.readline
>     return line
>    rescue => err
>     print "eek: #{err}\n"
>    end
>  end
>
>  def process
>    line = get_next_line
>    process_line(line)
>  end
>
> class bar < foo
>  def process_line(line)
>    .. do something with the line ..
>    .. write to a file ..
>  end
> end
>
> The problem is that the popen exits, typically with a
> non-zero exitcode (garbage at the end of the gzipped file).
> The next time the program does something in the
> process_line function - typically writing to a file,
> or reading/writing to/from the database - _that_
> operation generates an error.
>
> I assume I'm doing something wrong with respect to
> trapping the errors from the popen, but I'm baffled
> about exactly what I should do.
>
> Clues _very_ appreciated;  I've been bashing my head
> on this for a while.  Stuffing in lots and lots of
> begin / end checks around the operations in process_line
> typically does the trick, but it's very.. uhh, inelegant.
>
> Thanks!

not sure if it's important but

   irb(main):001:0> pipe = IO::popen 'bash -c exit'
   => #<IO:0xb73e0e1c>
   irb(main):002:0> pipe.read
   => ""
   irb(main):003:0> pipe.read
   => ""
   irb(main):004:0> pipe.read
   => ""
   irb(main):005:0> pipe.read
   => ""
   irb(main):006:0> pipe.read
   => ""

just because the process is dead - you still can 'read' from the pipe.

regards.

-a
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