On Thu, Jul 27, 2017 at 7:49 PM, Norman Gaywood <ngayw...@gmail.com> wrote:

> my $input = q:to/EOS/;
> line of text
> another line
> my $cat  = run 'cat', '-n', :in($input.print), :out;
> my $output = $cat.out.get;
> $cat.in.close;
> $cat.out.close;
> say "done";
> say $output;
> But that is not correct. I seem to be missing something.

:in, :out, :err want a filehandle (or will create one if you specify True,
which is what pair syntax gives you if you specify one of them without a
filehandle). Not a string; and .print applied to a Str does not turn the
string into a filehandle, it sends the string to the filehandle in $*OUT.

my $cat = run 'cat', '-n', :in, :out;
$cat.in.print($input); # this .print, on IO::Handle, prints the string to
that handle
my $output = $cat.out.slurp: :close;

Note that you need to be very careful to avoid the "open3" deadlock: pipes
have limited buffers, and if you do this all in one thread when the data is
large enough to block on write, and the receiving program then blocks on
write back to you, you will deadlock. No language can protect you from
this. The solution is that either the writer or the reader (or both) needs
to be in its own thread so that if one blocks, the other can keep running
and eventually clear the block.

brandon s allbery kf8nh                               sine nomine associates
allber...@gmail.com                                  ballb...@sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net

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