Perl's open() interface (and for that matter the underlying UNIX/Linux open(2) interface) don't allow you to specify a particular file descriptor.

Ah, my mistake. I was confused by the fact that C's fdopen(3) is on the same man-page as fopen(3). "fdopen" is mentioned in perldoc -f open when discussing open's '>&=6' syntax. I saw fopen(path, mode) and fdopen(fd, mode) and conflated the two's capabilities. (open a FILE* given a path, and open a FILE* given an fd number).

The usual way to handle this would be keep creating handles until the descriptor reaches the desired number.

Hmm. Looking at the source for sslclient, it seems the strategy is:

  1. Close fd's 6 and 7.
  2. Open a pipe.
  3. fd_move the pipe's ends to 6 and 7.

fd_move is a qmail-ism, apparently. It uses fcntl(current-fd,F_DUPFD,desired-fd) behind the scenes.

Note also that the parent should be creating a couple of pipes using the pipe() function to create the connections between parent and child.

Oops, yes. Thanks. Forgot in my for-this-node example that parent's "in" is child's "out" and vice versa.

For the curious, perldoc perlipc also suggests that my case warrants $SIG{PIPE} = 'IGNORE'; and $SIG{CHLD} = sub { }; # do something to handle a dead child

In reply to Re: Open a file on a specific file descriptor? by benizi
in thread Open a file on a specific file descriptor? by benizi

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.