my ($in, $out, $err) = (\*CHLD_IN, \*CHLD_OUT, \*CHLD_ERR);
    my $pid = open3($in, $out, $err, 'myprog -xyz blah')
        or die 'internal error';
    print $in "some input\n";
    close $in or die "$!: closing child STDIN\n";
    my @out = <$out>;    
    my @err = <$err>;
    close $out or die "$!: closing child STDOUT\n";    
    close $err or die "$!: closing child STDERR\n";    
    waitpid( $pid, 0 );
    my $chexit = $?;
    print STDERR @err;
    chomp @err;
    @err and exit $chexit >> 8;
    # output from subprocess is in @out ...
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As it turned out, for various reasons, I had to create an intermediate file anyway. But this example is just what I was after - many thanks, I will surely have use for it sometime soon.

I had not (didn't know about them). They certainly look interesting - I will check them out tomorrow.

Many thanks for the steer.