| 1 | ---
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| 2 | default_highlighter: oils-sh
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| 3 | ---
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| 4 |
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| 5 | Oils Headless Mode: For Alternative UIs
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| 6 | =======================================
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| 7 |
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| 8 | A GUI or [TUI][] process can start Oils like this:
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| 9 |
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| 10 | osh --headless
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| 11 |
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| 12 | and send messages to it over a Unix domain socket. In this mode, the language
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| 13 | and shell state are **decoupled** from the user interface.
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| 14 |
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| 15 | This is a unique feature that other shells don't have!
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| 16 |
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| 17 | [TUI]: https://en.wikipedia.org/wiki/Text-based_user_interface
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| 18 |
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| 19 | Note: This doc is **in progress**. Join the `#shell-gui` channel on
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| 20 | [Zulip]($xref:zulip) for current information.
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| 21 |
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| 22 | <div id="toc">
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| 23 | </div>
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| 24 |
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| 25 | ## The General Idea
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| 26 |
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| 27 | The UI process should handle these things:
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| 28 |
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| 29 | - Auto-completion. It should use Oils for parsing, and not try to parse shell
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| 30 | itself!
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| 31 | - History: Allow the user to retrieve commands typed in the past.
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| 32 | - Cancelling commands in progress.
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| 33 | - Optional: multiplexing among multiple headless shells.
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| 34 |
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| 35 | The shell process handles these things:
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| 36 |
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| 37 | - Parsing and evaluating the language
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| 38 | - Maintaining state (shell options, variables, etc.)
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| 39 |
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| 40 | ## How to Write a Client for a Headless Shell
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| 41 |
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| 42 | ### Implement the FANOS Protocol
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| 43 |
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| 44 | FANOS stands for *File descriptors and Netstrings Over Sockets*. It's a
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| 45 | **control** protocol that already has 2 implementations, which are very small:
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| 46 |
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| 47 | - [client/py_fanos.py]($oils-src): 102 lines of code
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| 48 | - [cpp/fanos_shared.c]($oils-src): 215 lines of code
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| 49 |
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| 50 | ### Send Commands and File Descriptors to the "Server"
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| 51 |
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| 52 | List of commands:
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| 53 |
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| 54 | - `EVAL`. Parse and evaluate a shell command. The logic is similar to the
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| 55 | `eval` and `source` builtins.
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| 56 | - It can be used for both user-entered commands and "behind the scenes"
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| 57 | functions for the shell UI.
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| 58 | - The stdin, stdout, and stderr of **the shell and its child processes** will
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| 59 | be redirected to the descriptors you pass.
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| 60 | - There's no history expansion for now. The UI can implement this itself,
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| 61 | and Oils may be able to help.
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| 62 |
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| 63 | TODO: More commands.
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| 64 |
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| 65 | ### Query Shell State and Render it in the UI
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| 66 |
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| 67 | You may want to use commands like these to draw the UI:
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| 68 |
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| 69 | - `echo ${PS1@P}` -- render the prompt
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| 70 | - `echo $PWD $_` -- get the current directory and current status
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| 71 |
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| 72 | You can redirect them to a pipe, rather than displaying them in the terminal.
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| 73 |
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| 74 | Remember that a fundamental difference between a REPL and a GUI is that a GUI
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| 75 | **shows state** explicitly. This is a good thing and you should take advantage
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| 76 | of it!
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| 77 |
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| 78 | ### Example Code
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| 79 |
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| 80 | See [client/headless_demo.py]($oils-src). This is pure Python code that's
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| 81 | divorced from the rest of Oils.
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| 82 |
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| 83 | ## Related Links
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| 84 |
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| 85 | Feel free to edit these pages:
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| 86 |
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| 87 | - [Headless Mode][] on the wiki. We want there to be a rich ecosystem of
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| 88 | interactive shells built upon Oils.
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| 89 | - [Interactive Shell][] on the wiki. Be inspired by these nice projects, many
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| 90 | of which have screenshots!
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| 91 |
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| 92 | [Headless Mode]: https://github.com/oilshell/oil/wiki/Headless-Mode
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| 93 |
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| 94 | [Interactive Shell]: https://github.com/oilshell/oil/wiki/Interactive-Shell
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