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About

Helic is a tool for synchronizing clipboard contents across X11, tmux and network, consisting of a daemon listening for changes and a CLI client for use in programs like Neovim.

X11 has three separate copy buffers, called the clipboard, the primary selection and the secondary selection. Selections are used when text is selected with the mouse, while the clipboard is updated by Ctrl-C.

When some text is copied or selected in X11, the daemon receives an event that it proceeds to broadcast to the configured targets. If the source was a selection, the X11 clipboard is updated as well.

The CLI program hel can be used to manually send text to the daemon, for example from tmux or Neovim. If remote hosts are configured, each yank event is sent over the network to update their clipboards.

Several yank events are stored in memory in order to detect duplicates and cycles.

The CLI understands four different commands:

Command Meaning
hel listen Start the daemon. This is best done from a systemd user service.
hel yank Send standard input or argument to the daemon as a manual yank event.
hel list Print the event history.
hel load Load an older event to the clipboard, given its index into the history.

The list command will print a table like this:

╭───┬──────────┬───────┬──────────┬──────────────────────────╮
│ # │ Instance │ Agent │   Time   │         Content          │
╞═══╪══════════╪═══════╪══════════╪══════════════════════════╡
│ 2 │   test   │ nvim  │ 12:00:00 │ single line              │
├───┼──────────┼───────┼──────────┼──────────────────────────┤
│ 1 │   test   │ nvim  │ 12:00:00 │ single line with newline │
├───┼──────────┼───────┼──────────┼──────────────────────────┤
│ 0 │   test   │ nvim  │ 12:00:00 │ three lines 1 [3 lines]  │
╰───┴──────────┴───────┴──────────┴──────────────────────────╯

The index in the first column, with 0 being the latest event, can be used with hel load.

Installing and Running Helic

Nix

The project uses a Nix flake to configure its build, and it is recommended to install or run it using Nix as well. If Nix is installed and configured for use with flakes, the app can be run without installation like this:

$ nix run github:tek/helic -- listen
$ echo 'yank me' | nix run github:tek/helic -- yank --agent cli
$ nix run github:tek/helic -- list 100
$ nix run github:tek/helic -- load 5

NixOS

The flake provides a NixOS module that can be used by adding it to /etc/nixos/flake.nix:

{
  inputs.helic.url = "github:tek/helic";
  outputs = { nixpkgs, helic, ... }: {
    nixosConfigurations.myhost = nixpkgs.lib.nixosSystem {
      modules = [helic.nixosModules.default];
      services.helic.enable = true;
    };
  };
}

With this, a systemd user service will be started on login and the client will be in $PATH:

$ echo 'yank me' | hel yank
$ hel yank --agent custom-name --text 'yank me'

After a rebuild, the service may not be started right away, so this command must be executed:

$ systemctl --user start helic

Globally enabled systemd user services are started for all users on login. To prevent that, you can set the module option services.helic.user = "myuser".

Without Nix

Alternatively, the app can be installed using a Haskell package manager, like Cabal:

$ cabal install helic
$ hel listen

CLI

If no command has been specified explicitly, Helic decides which one to start by the presence of stdin data:

$ hel # start daemon
$ echo 'yank me' | hel # yank

Global CLI options are specified before the command name, command-specific ones after it.

Command Name Description
Global --verbose Increase the log level.
Global --config-file FILE Use the specified file path instead of the default locations.
listen --agent NAME Used to avoid sending yanks back to the application that sent them.
list positional (hel list 5) Limit the number of printed events.
load positional (hel load 5) Choose the index of the event to be loaded.
yank --agent NAME Custom name used in the list output and to avoid cycles.
yank --text TEXT Yank text, uses stdin if not specified.

Configuring Helic

The app reads the first existing one of these three configuration files:

  • The file specified with --config-file
  • $XDG_CONFIG_DIR/helic.yaml (most likely ~/.config/helic.yaml)
  • /etc/helic.yaml

An example config file looks like this:

name: myhost
maxHistory: 1000
debounceMillis: 3000
verbose: true
net:
  enable: true
  port: 10001
  hosts:
    - "remote1:1000"
    - "remote2:2000"
  timeout: 5
tmux:
  enable: true
  exe: /bin/tmux
x11:
  enable: true
  display: ":0"

For NixOS, the file /etc/helic.yaml is generated from module options:

{
  services.helic = {
    enable = true;
    name = "myhost";
    maxHistory = 1000;
    debounceMillis = 3000;
    verbose = true;
    user = "myuser";
    net = {
      enable = true;
      port = 10001;
      hosts = ["remote1:1000" "remote2:2000"];
      timeout = 5;
    };
    tmux = {
      enable = true;
      package = pkgs.tmux;
    };
    x11 = {
      enable = true;
      display = ":0";
    };
  };
}

The meaning of these options is:

Key Default Description
name Host name An identifier for the host, used for filtering duplicates.
user null Only for NixOS: If set, only start the service for that user.
maxHistory 100 The number of yanks that should be kept.
debounceMillis 3000 The interval in milliseconds during which the same text is ignored.
verbose Increase the log level.
net.enable true Whether to send events over the network.
net.port 9500 The HTTP port the daemon listens to for both remote sync and hel yank.
net.hosts [] The addresses (with port) of the hosts to which this instance should broadcast yank events.
net.timeout 300 The timeout in milliseconds for requests to remote hosts.
tmux.enable true Whether to send events to tmux.
tmux.package pkgs.tmux Only for NixOS: The nixpkgs package used for the tmux executable.
tmux.exe tmux Only for YAML file: The path to the tmux executable
x11.enable true Whether to synchronize the X11 clipboard.
x11.display :0 The display identifier used when connecting to the default display via GTK fails.

Neovim

Neovim's clipboard requires configuration with a tool in any case, so changing it to use hel is simple:

let g:clipboard = {
  \   'name': 'helic',
  \   'copy': {
  \      '+': 'hel yank --agent nvim',
  \      '*': 'hel yank --agent nvim',
  \    },
  \   'paste': {
  \      '+': 'xsel -bo',
  \      '*': 'xsel -bo',
  \   },
  \ }

Since Helic updates the X11 clipboard, a custom paste command is not necessary.