How can I pipe two Perl CORE::system commands in a cross-platform way?
- by Pedro Silva
I'm writing a System::Wrapper module to abstract away from CORE::system and the qx operator. I have a serial method that attempts to connect command1's output to command2's input. I've made some progress using named pipes, but POSIX::mkfifo is not cross-platform.
Here's part of what I have so far (the run method at the bottom basically calls system):
package main;
my $obj1 = System::Wrapper->new(
interpreter => 'perl',
arguments => [-pe => q{''}],
input => ['input.txt'],
description => 'Concatenate input.txt to STDOUT',
);
my $obj2 = System::Wrapper->new(
interpreter => 'perl',
arguments => [-pe => q{'$_ = reverse $_}'}],
description => 'Reverse lines of input input',
output => { '>' => 'output' },
);
$obj1->serial( $obj2 );
package System::Wrapper;
#...
sub serial {
my ($self, @commands) = @_;
eval {
require POSIX; POSIX->import();
require threads;
};
my $tmp_dir = File::Spec->tmpdir();
my $last = $self;
my @threads;
push @commands, $self;
for my $command (@commands) {
croak sprintf
"%s::serial: type of args to serial must be '%s', not '%s'",
ref $self, ref $self, ref $command || $command
unless ref $command eq ref $self;
my $named_pipe = File::Spec->catfile( $tmp_dir, int \$command );
POSIX::mkfifo( $named_pipe, 0777 )
or croak sprintf
"%s::serial: couldn't create named pipe %s: %s",
ref $self, $named_pipe, $!;
$last->output( { '>' => $named_pipe } );
$command->input( $named_pipe );
push @threads, threads->new( sub{ $last->run } );
$last = $command;
}
$_->join for @threads;
}
#...
My specific questions:
Is there an alternative to POSIX::mkfifo that is cross-platform? Win32 named pipes don't work, as you can't open those as regular files, neither do sockets, for the same reasons.
2. The above doesn't quite work; the two threads get spawned correctly, but nothing flows across the pipe. I suppose that might have something to do with pipe deadlocking or output buffering. What throws me off is that when I run those two commands in the actual shell, everything works as expected.
Point 2 is solved; a -p fifo file test was not testing the correct file.
