I have a need to run a command in a subprocess, posting a series of data lines, and reading back its stdout.

Reading the friendly manual gives an example with open2, but with some words of warning.

The problem with this is that Unix buffering is really going to ruin your day. Even though your Writer filehandle is auto-flushed, and the process on the other end will get your data in a timely manner, you can't usually do anything to force it to give it back to you in a similarly quick fashion. In this case, we could, because we gave cat a -u flag to make it unbuffered. But very few Unix commands are designed to operate over pipes, so this seldom works unless you yourself wrote the program on the other end of the double-ended pipe.
It then talks about a require module comm.pl, which uses pttys, then going on to state that this will be replaced with IPC::Chat (which does not exist - yet).

Has anyone done this kind of thing? The application I am forking is a third party program, and I have no control of how it buffers its stdout. It also has the nasty that it causes database timeouts and locking problems if the stdout is not read quickly enough.

Any help would be appreciated.

--rW

In reply to Bi-directional IPC without tears by rinceWind

Title:
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, details, 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, summary, 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.