From: "David G. Andersen" <dga@...>
Date: 2004-10-16T10:49:28+09:00
Subject: Popen and operations failing later

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!

  -dave

-- 
work: dga@lcs.mit.edu                          me:  dga@pobox.com
      MIT Laboratory for Computer Science           http://www.angio.net/