flipper has asked for the wisdom of the Perl Monks concerning the following question:

Hello Monks,

I'm using fork() exec() and socketpair() to start a child and capture its output, something like
socketpair($r_stdout, $w_stdout, AF_UNIX, SOCK_STREAM, PF_UNSPEC);
socketpair($r_stderr, $w_stderr, AF_UNIX, SOCK_STREAM, PF_UNSPEC);

if(fork()){
                close $w_stdout;
                #read from $r_stdout etc
}else{
                my $so_fd=fileno($w_stdout);
                open STDOUT, ">&$so_fd";
                exec('something') or die;
}

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The problem I have is I have to exec and capture the output of a script which writes to FD3, something like perl -e 'open STDOUT, ">&3";print  "hello, world\n"'
so I'd like to open fd3 to one half of a socketpair - is this possible? The loose equivalent of bash exec 3>/tmp/z

I guess I'd have to be careful not to clobber any of my socketpairs...

Thanks!

Replies are listed 'Best First'.
Re: working with files by number
by flipper (Beadle) on Mar 24, 2009 at 16:42 UTC
    got it...
    if(fork()){
                #read
}else{
                my $so_fd=fileno($w_stdout);
                my $se_fd=fileno($w_stderr);
                my $si_fd=fileno($r_stdin);
#
# fd3 must be $w_fd3, so backup current fd3, and reopen 3 to $w_fd3
#
                my $old3=dup(3);
                my $new3=dup2(fileno($w_fd3), 3);
#
# then if any of the other fd's we were going to use was 3, change it 
+to the backup fd
#
                for my $i ($so_fd, $se_fd, $si_fd){
                        if ($i == 3){
                                $i=$old3;
                        }
                }
                open STDOUT, ">&$so_fd";
                open STDERR, ">&$se_fd";
                open STDIN, "<&$si_fd";

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[d/l]
      For the interested, dup and dup2 are located in POSIX.
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