Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

It would help to see the exact code and output from a failure. I still don't understand 100% but it sounds like your failure is on the read side -- that you try reading from the device and get an empty "line". In the first read examples, you're opening the device with O_NDELAY. If I remember correctly, on most *nix systems, the way that behaves with a terminal device is that it returns nothing if nothing is available on the terminal at the time of the read. It seems like that behavior may be matching exactly what you're seeing. I also believe that an open using O_NDELAY may itself return immediately, before the terminal device is ready, which could cause problems that only show up when timing changes.

In general, reading directly from terminal devices like this is tricky and error prone. So you may want to revisit exactly what it is you're trying to achieve -- something else I can't really gather from the example so far. The last open is cat'ing the terminal device and reading from that output. That should do almost the same thing the opens before it are attempting, but it should avoid the O_NDELAY issues ... I think. It would help to know the context the terminal device is bneing read in -- what's being typed there, how that device relates to the one the program is running on, etc.

In reply to Re^3: Wierd File pipe problem... by steves
in thread Wierd File pipe problem... by bferlin

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others musing on the Monastery: (10)
    As of 2019-05-24 17:25 GMT
    Find Nodes?
      Voting Booth?
      Do you enjoy 3D movies?

      Results (150 votes). Check out past polls.

      • (Sep 10, 2018 at 22:53 UTC) Welcome new users!