class X::Proc::Async::OpenForWriting is Exception {}

When a Proc::Async object is opened only for reading from the external program (no :w passed to open), and a write operation such as write, print and say is performed, an exception of type X::Proc::Async::OpenForWriting is thrown:

my $proc = Proc::Async.new("echo");
$proc.start;
$proc.say(42);
CATCH { default { put .^name, ': ', .Str } };
# OUTPUT: «X::Proc::Async::OpenForWriting: Process must be opened for writing with :w to call 'say'␤»

To fix that you can use writable commands with :w flag:

my $prog = Proc::Async.new(:w, 'cat');
$prog.stdout.tap( -> $str {
    print $str;
});
my $promise = $prog.start;
await $prog.say('foo');
$prog.close-stdin;
await $promise;

Methods

method method

method method(X::Proc::Async::OpenForWriting:D:)

Returns the method name that was called and which caused the exception.