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working with files by number

by flipper (Beadle)
on Mar 24, 2009 at 14:18 UTC ( #752882=perlquestion: print w/replies, xml ) Need Help??

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; }


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";
      For the interested, dup and dup2 are located in POSIX.

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