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#!/usr/bin/perl -w
#hooks up two processes, 2nd of which has one line of output per line of input, expected by the first, which starts off the communication
# if you don't know how to fork/exec in a C program, this could be helpful under limited cirmustances (would be ok to liaise with sentserver)
#WARNING: because it waits for the result from command 2 after sending every line, and especially if command 1 does the same, using sentserver as command 2 won't actually buy you any real parallelism.
use strict;
use IPC::Open2;
use POSIX qw(pipe dup2 STDIN_FILENO STDOUT_FILENO);
#use IO::Handle;
$,=' ';
my $quiet=$ENV{QUIET};
sub info {
print STDERR @_ unless $quiet;
}
my @c1;
if (scalar @ARGV) {
do {
push @c1,shift
} while scalar @ARGV && $c1[$#c1] ne '--';
}
pop @c1;
my @c2=@ARGV;
@ARGV=();
(scalar @c1 && scalar @c2) || die "usage: $0 cmd1 args -- cmd2 args; hooks up two processes, 2nd of which has one line of output per line of input, expected by the first, which starts off the communication. crosses stdin/stderr of cmd1 and cmd2 line by line (both must flush on newline and output. cmd1 initiates the conversation (sends the first line). QUIET=1 env var suppresses debugging output. default: attempts to cross stdin/stdout of c1 and c2 directly (via two unidirectional posix pipes created before fork). env SERIAL=1: (no parallelism possible) but lines exchanged are logged unless QUIET. if SNAKE then stdin -> c1 -> c2 -> c1 -> stdout";
info("1 cmd:",@c1,"\n");
info("2 cmd:",@c2,"\n");
sub lineto {
select $_[0];
$|=1;
shift;
print @_;
}
my $snake=$ENV{SNAKE};
my $serial=$ENV{SERIAL};
if ($serial || $snake) {
my ($R1,$W1,$R2,$W2);
my $c1p=open2($R1,$W1,@c1); # Open2 R W backward from Open3.
my $c2p=open2($R2,$W2,@c2);
if ($snake) {
while(<STDIN>) {
lineto($W1,$_);
last unless defined ($_=<$R1>);
lineto($W2,$_);
last unless defined ($_=<$R2>);
lineto($W1,$_);
last unless defined ($_=<$R1>);
lineto(*STDOUT,$_);
}
} else {
while(<$R1>) {
info("1:",$_);
lineto($W2,$_);
last unless defined ($_=<$R2>);
info("2:",$_);
lineto($W1,$_);
}
}
} else {
my @rw1=POSIX::pipe();
my @rw2=POSIX::pipe();
my $pid=undef;
$SIG{CHLD} = sub { wait };
while (not defined ($pid=fork())) {
sleep 1;
}
POSIX::close(STDOUT_FILENO);
POSIX::close(STDIN_FILENO);
if ($pid) {
POSIX::dup2($rw1[1],STDOUT_FILENO);
POSIX::dup2($rw2[0],STDIN_FILENO);
exec @c1;
} else {
POSIX::dup2($rw2[1],STDOUT_FILENO);
POSIX::dup2($rw1[0],STDIN_FILENO);
exec @c2;
}
while (wait()!=-1) {}
}
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