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 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.

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 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/configuration.nix:

{
  inputs.helic.url = github:/tek/helic;
  outputs = { nixpkgs, helic, ... }: {
    nixosConfigurations.myhost = nixpkgs.lib.nixosSystem {
      modules = [helic.nixosModule];
      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

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

$ systemctl --user start helic

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.

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
net:
  port: 10001
  hosts:
    - "remote1:1000"
    - "remote2:2000"
  timeout: 5
tmux:
  enable: true
  exe: /bin/tmux

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

{
  services.helic = {
    enable = true;
    name = "myhost";
    maxHistory = 1000;
    net = {
      port = 10001;
      hosts = ["remote1:1000" "remote2:2000"];
      timeout = 5;
    };
    tmux = {
      enable = true;
      package = old.tmux;
    };
  };
}

The meaning of these options is:

Key	Default	Description
name	Host name	An identifier for the host, used for filtering duplicates.
maxHistory	100	The number of yanks that should be kept.
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

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.