Pipe in Zig. Notice that EOF can only be read once child or parent close the pipe. Doesnt matter if we dup or not.

pipe.zig

const std = @import("std");
const os = std.os;
pub fn main() !void {
    const alloc = std.testing.allocator;
    const pipe = try os.pipe(); // read end [0], write end [1]
    const read_dup = try os.dup(pipe[0]);
    const write_dup = try os.dup(pipe[1]); // for simplicity

    const pid_result = try os.fork();
    if (pid_result == 0) {
        std.debug.print("child spawned\n", .{});
        // we are the child
        const rd_pipe = std.fs.File{ .handle = read_dup };
        os.close(pipe[0]);
        os.close(pipe[1]);
        os.close(write_dup);

        const content = try rd_pipe.reader().readAllAlloc(alloc, 10_000);
        std.debug.print("content: {s}\n", .{content});
        // usually we exec here, but in this example we do something simpler
        rd_pipe.close();
    } else {
        std.debug.print("parent spawned\n", .{});
        // we are the parent
        const wr_pipe = std.fs.File{ .handle = pipe[1] };
        os.close(pipe[0]); // close read end
        os.close(read_dup);
        os.close(write_dup);

        try wr_pipe.writer().writeAll("test123123123123123123blablabla\n"); // no \n to test things
        std.debug.print("waiting for child to print stuff\n", .{});
        while (true) {
            std.time.sleep(1_000_000_000);
            std.debug.print("tick\n", .{});
        }
        wr_pipe.close(); // close write end
        // we must close or think of a delimiter
    }
}