Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.jpl.nasa.gov (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: What am I missing from chat2.pl?
Message-ID: <1991Jun10.173227.4630@jpl-devvax.jpl.nasa.gov>
Date: 10 Jun 91 17:32:27 GMT
References: <1991May27.120442.16645@colorado.edu> <1991May27.160539.8127@iWarp.intel.com> <1991May27.215623.20884@colorado.edu>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 47

In article <1991May27.215623.20884@colorado.edu> frechett@spot.Colorado.EDU (-=Runaway Daemon=-) writes:
: Here's the situation.. I have a client (addapted from the in the man pages)
: and I want to be able to poll stdin and the socket both.. Was hoping to 
: find something in chat2.pl but if you haven't written a select then I 
: suspect that I am am going to have a bit of aproblem..   
: 
: It is a simple matter to listen to the socket and parse what I see and 
: such.. OR to listen to the users's input but as soon as I start to try to 
: deal with both.. it stalls on something.. Here is a code fragment...
: 
: S is the socket.. 
: 
: sub fhbits {
: 	local(@fhlist) = split(' ',$_[0]);
: 	local($bits);
: 	for (@fhlist) {
: 		vec($bits,fileno($_),1)=1;
: 	}
: 	$bits;
:     }
: $rin = "";
: $rin = &fhbits('stdin S');
: # the problem here is that I don't see ANYTHING in $rin  Is it 
: # unprintable.. and just what the hell is it anyway.. 

It's a bit vector, 8 bits to the byte, so of course it's not guaranteed
to be printable.  You get the bits out with vec() just like you put them in.
Alternately, use unpack('b*', ...) to turn it into a string of 0's and 1's.

:                if ($child = fork) {
:                      for (;;) {
: # it pauses here fine.. waiting for something to come through.. 
: ($nfound) = select($rout=$rin, undef,undef,undef);
: # but I am totally stuck here... I couldn't see what $rin was and I can't 
: # see what $rout is.. so I don't know what filedescriptors are ready.. 
: # not only that but when I put in a line like... 
: if ($nfound == 1) { read(S,$output,1024); print "$output"; } 
: # and then sent it only stuff through the socket.. it still wasn't 
: # trapping it.. It just froze stdin of course.. It just displays what is 
: # coming throught the socket but the select didn't see it and read didn't see
: # it..   What's wrong?

read() calls C's fread() function, which is going to try to read 1024 bytes
come hell or high water (or both, if too many snowballs melt there).  Use
sysread() instead--that's one of the reasons it's there.

Larry