tmux.rb

tmux.rb is a Ruby DSL that compiles readable, structured block-based configuration into native tmux configuration and format strings.

At a glance

A small, hand-written ~/.tmux.conf:

set -g prefix C-a
unbind C-b
bind C-a send-prefix

set -g mouse on
set -g base-index 1
setw -g mode-keys vi

bind | split-window -h -c "#{pane_current_path}"
bind - split-window -v -c "#{pane_current_path}"
bind r source-file ~/.tmux.conf \; display-message "Reloaded"

set -g status-right "#{?window_zoomed_flag,#[fg=yellow]ZOOM #[fg=default],}#S"

The same configuration in tmux.rb, which compiles to a file tmux loads identically:

Tmux.configure do
  global.prefix = "C-a"
  unbind "C-b"
  bind("C-a").command(:send_prefix)

  global.mouse = true
  global.base_index = 1
  window.mode_keys = :vi

  bind("|").split(:h, cwd: :current)
  bind("-").split(:v, cwd: :current)
  bind("r")
    .source("~/.tmux.conf")
    .display_message("Reloaded")

  global.status.right = Tmux.format do
    if?(Tmux.window_zoomed_flag) do
        style(fg: :yellow) { text "ZOOM " }
    end
    text Tmux.session_name
  end
end

The payoff grows with the configuration. Status lines are where hand-written tmux gets hardest to read, and where the format DSL helps most:

# ~/.config/tmux/tmux.rb
Tmux.configure do
  global.prefix = "C-s"     # set-option -g prefix "C-s"
  global.mouse = true       # set-option -g mouse on
  window.mode_keys = :vi    # set-option -gw mode-keys "vi"

  global.status.right = Tmux.format do
    if?(Tmux.window_zoomed_flag) do
        left_flag "Z", bg: :white, fg: :black, attrs: :bold
    end
    left_segment Tmux.pane_current_command, bg: :colour238, fg: :white
    left_segment "#{Tmux.session_name}@#{Tmux.host}", bg: :blue, fg: :black
  end

  bind("|").split(:horizontal, cwd: :current)
end

tmux.rb build ~/.config/tmux/tmux.rb --output ~/.tmux.conf

Screenshot: the status line this configuration draws, in a zoomed window

Screenshots in this README are real tmux sessions rendering the example just above them (how they are made). They use the Catppuccin Mocha terminal color scheme and JetBrains Mono Nerd Font, with the status bar set to the terminal's own colors. Named colors such as :blue, :white, or colour1 take their shade from your terminal's color scheme; colour16 to colour255 and hex colors such as "#ff8800" look the same everywhere. Powerline edges need a font with Powerline glyphs, such as a Nerd Font.

Examples

examples/author_config.rb is the author's complete tmux configuration: structured status bars, pane borders, and window tabs, plus integration with tmux-ai-attn.
examples/popular_configs contains ten ports of well-known public tmux configurations. Each pinned upstream config sits beside its Ruby version for comparison.
examples/window_status.rb is a standalone format file.

Why

Hand-written tmux configuration gets hard to change once it grows: status lines become deeply nested #{?...,...,...} expressions where a misplaced comma silently breaks rendering, and every level of quoting has to be escaped by hand. tmux.rb keeps tmux's model but lets you write it as ordinary Ruby.

Compile, don't interpret. Ruby runs only while you build or validate a configuration. The output is plain tmux configuration, and tmux evaluates its own formats, so rendering the status line never spawns Ruby and needs nothing installed beyond tmux.
Skip manual escaping. Write text, styles, variables, and conditionals directly, without managing nested tmux quoting and escaping.
Keep tmux within reach. The DSL adds readable names and helpers but hides nothing: any option, command, or format string can still be written directly, and raw passes tmux commands through verbatim.
Generate deterministic output. The same source always produces byte-identical configuration, so the generated file is easy to review and compare in version control.
Treat the live server as a boundary. build, check, and diff never touch a running tmux server; only an explicit load does.

Installation

gem install tmux

tmux.rb needs Ruby 3.2 or newer. The full DSL is tested on tmux 3.2 and newer. Compilation requires the target tmux executable to be installed.

The gem installs the tmux.rb command (also available as tmux_rb). Ruby code that uses the library directly loads it with require "tmux".

Configuration files

Tmux.configure builds configuration commands: option setters, key bindings, and other tmux commands. Tmux.format builds one reusable value, such as the contents of status-right, which those commands can assign to an option.

A configuration file ends with either resulting object (Tmux::Config or Tmux::Format). Run it with the tmux.rb command, or use Tmux.load_file("config.rb") from Ruby. Constants and helper methods defined at the top level stay local to that file.

Configuration files are trusted code. build, check, diff, and load all execute them, with the same access as a Ruby script. Only build configurations you would be willing to run as a script. A binding created with load_config re-runs its Ruby file every time the key is pressed.

Blocks and helper methods

Inside Tmux.configure and Tmux.format blocks, call DSL methods directly. Methods you def and instance variables you set in a block stay visible in its nested blocks, including conditional branches. Local variables and lambdas work throughout the blocks too.

Give a block one parameter to keep Ruby's normal scoping, with the builder passed in:

def status_color = "colour37"

Tmux.configure do |c|
  # self is unchanged here, so status_color is the method defined above.
  c.global.status.style = "fg=#{status_color}" # set-option -g status-style "fg=colour37"
end

CLI

tmux.rb build config.rb                    # print the generated configuration
tmux.rb build config.rb --output tmux.conf # write it atomically
tmux.rb check config.rb                    # ask an isolated tmux server to parse it
tmux.rb diff  config.rb ~/.tmux.conf       # unified diff; exit 0 means identical
tmux.rb load  config.rb                    # compile and source into a tmux server
tmux.rb load  -S /tmp/outer.sock config.rb # ...into the server at a socket path
tmux.rb load  -L work config.rb            # ...or the server with a socket name
tmux.rb --version

Every command accepts --help.

build --output updates the destination atomically. A symlinked destination (such as a ~/.tmux.conf that points into a dotfiles repository) is followed rather than replaced, and an existing file keeps its permissions.
check checks tmux syntax in an isolated server, including commands inside if? branches. Option names and scopes are already checked during compilation. It does not apply commands or validate option values. Loading the file into an isolated server checks values too: tmux -L scratch -f /dev/null new-session -d 'sleep 600', then tmux -L scratch source-file tmux.conf.
load sources the result into the server $TMUX names, or into the one given with -S SOCKET or -L NAME. Pass one of those from inside a nested tmux, where $TMUX names the inner server.

Errors raised while evaluating a configuration are reported with the file and line that caused them.

Target tmux version

By default, configurations target the tmux on your PATH. All built-in option names and scopes are checked against that executable's supported options. To build for a different version, select its executable with --tmux:

tmux.rb build config.rb --tmux /opt/tmux-3.3/bin/tmux
tmux.rb check config.rb --tmux /opt/tmux-3.3/bin/tmux
tmux.rb load -S /tmp/outer.sock config.rb --tmux /opt/tmux-3.3/bin/tmux

From Ruby, use Tmux.load_file("config.rb", tmux: "/opt/tmux-3.3/bin/tmux") or Tmux.configure(tmux: "/opt/tmux-3.3/bin/tmux") { ... }. load refuses to apply a configuration if the destination server's version does not match the selected executable. Use tmux_from and tmux_below for settings that differ between versions; only the applicable version branch's options are checked.

Format DSL

Use Tmux.format for status lines, window tabs, pane borders, and anywhere else tmux expands formats. Assign the resulting format to an option to use it in a configuration:

# A window tab: the index in a colored block, then the name, which turns
# yellow while a flash is lit.
flash = Tmux.user_option(:@attn_flash)
phase = Tmux.user_option(:@attn_phase)

Tmux.format do
  # Set the foreground and background for what follows.
  style fg: :white, bg: :colour238
  # Literal text with the window index interpolated; it stays dynamic.
  text " #{Tmux.window_index} "
  # The name's colors: black on yellow while flashing, grey otherwise.
  if?(flash && phase) do
    style fg: :black, bg: :yellow
  end.else do
    style fg: :colour250, bg: :colour236
  end
  # The window name, padded with a space on each side.
  text " #{Tmux.window_name} "
  # Return to the default style so nothing leaks into the next tab.
  reset_style
end

Screenshot: three windows drawn with this format, the last one mid-flash

The sections below cover each part of the format DSL. Most calls can be chained; if? supports .elsif? and .else branches.

Text

text adds text that tmux shows as written. Expressions interpolated into the string stay dynamic. Other characters, including #, %, ,, and }, print literally, even inside conditional branches.

Tmux.format do
  # " 3 " for window 3: the interpolated index stays a tmux variable.
  text " #{Tmux.window_index} "
  # Expressions can also be passed as separate parts.
  text "[", Tmux.session_name, "]"
  # "#", "%", and "," print literally, even inside a conditional.
  if?(Tmux.pane_active) { text "#1, 50%" }
  # literal: true prints a string exactly as written, format code included.
  text "\#{not_a_variable}", literal: true
end

text rejects #[ and #( in a string, since styles and shell commands have their own methods (style and command).

Dates and times

strftime adds a date/time format that tmux expands each time it renders. Unlike text, its % codes are kept.

Tmux.format do
  # "Tue 14:05", refreshed with the status line.
  strftime "%a %H:%M"
end

Appending expressions, formats, and format code

append adds tmux format source as is: an expression, a format built elsewhere, or a string of tmux format code. Unlike text, a string given to append is format code, not literal text.

clock = Tmux.format { strftime "%H:%M" }

Tmux.format do
  # An expression.
  append Tmux.pane_current_path
  # Another format.
  append clock
  # Raw tmux format code, for anything the DSL has no helper for.
  append "\#{t:window_activity}"
end

Shell commands

command adds a #(...) shell command, which tmux runs in the background and replaces with its output. Its text is format source, so #{...} codes expand before the shell sees it. Commands must have balanced parentheses.

Tmux.format do
  # The current git branch of the active pane's directory.
  command "git -C \#{pane_current_path} branch --show-current"
end

Styles

style sets colors and attributes for what follows; reset_style returns to the default. Given a block, style applies only to the block's content, which p: pads with spaces on both sides, and the style from before the block returns after it.

Tmux.format do
  # Colors and attributes as a hash.
  style fg: "#000000", bg: "#ff0000", attrs: :bold
  text " warning "
  # Attribute names alone.
  style :nobold
  # A styled, padded block: the window index in white on blue.
  style(fg: "#ffffff", bg: :blue, p: 1) do
    append Tmux.window_index
  end
  # After the block, the black on red from before it returns.
  text " here "
  # Back to the default style.
  reset_style
end

Screenshot: this format in the status line

Conditionals

if? chooses content each time tmux renders. It includes its block when the condition is true; use ! to negate a condition. Chain .else on if? for the false branch, or omit it to emit nothing when false. Add .elsif?(condition) for more branches; the first matching branch wins. Every branch can contain any format DSL calls, including nested conditionals.

See Expressions and conditions for variables, comparisons, and combining tests with &&, ||, and !. The same tests work in configuration conditionals.

Tmux.format do
  # Show "(name)" when the window is zoomed, the plain name otherwise.
  if?(Tmux.window_zoomed_flag) do
    text "(#{Tmux.window_name})"
  end.else do
    append Tmux.window_name
  end
  # Show a marker unless the pane is in a mode (copy mode, for example).
  if?(!Tmux.pane_in_mode) { text " *" }
  # Show " sync" first, otherwise " mode" in copy mode, or " async".
  if?(Tmux.pane_synchronized) do
    text " sync"
  end.elsif?(Tmux.pane_in_mode) do
    text " mode"
  end.else do
    text " async"
  end
end

Screenshot: this format in a zoomed window

Outside a format block, Tmux.if? builds a reusable conditional format with the same .elsif? and .else chain. Its branches use the format DSL; assign the result to an option or append it inside another format:

label = Tmux.if?(Tmux.pane_in_mode) do
  text "copy"
end.elsif?(Tmux.client_prefix) do
  text "prefix"
end.else do
  text "normal"
end

Tmux.configure do
  global.status.left = label
  global.status.right = Tmux.format do
    text "["
    append label
    text "]"
  end
end

Value and style switches

Use a conditional chain to choose which format DSL calls run. Use switch to choose a value to pass to a call, such as a color for fg: or bg:. The returned expression can be reused across styles or formats.

Call switch inside Tmux.format or Tmux.configure blocks, or Tmux.switch outside them. Both calls build the same kind of expression; choosing a value does not itself add content or configuration commands.

Both choose the first matching condition when tmux renders. A switch requires an else: value; a conditional chain can omit .else to emit nothing when no condition matches.

switch_style chooses a set of style attributes for the content that follows. It takes the same mapping as switch, with style hashes as the choices, and is shorthand for a conditional chain whose branches only call style.

Tmux.format do
  # Orange while the prefix key is held, green in copy mode, grey otherwise.
  background = switch(
    Tmux.client_prefix => "#FF8800",
    Tmux.pane_in_mode => "#6A9955",
    else: "#A6ADC8"
  )
  # Use that color as a background.
  style(fg: :black, bg: background, p: 1) { append Tmux.session_name }
  # Back to the default style, then a space.
  reset_style
  text " "
  # Choose an entire style: red when input is off, blue otherwise.
  switch_style(Tmux.pane_input_off => {fg: :red}, else: {fg: :blue})
  text "#{Tmux.pane_index}"
end

switch values can contain tmux format code. For literal text, use text inside a conditional branch instead.

Screenshot: this format with pane input disabled, with the prefix held, and in copy mode

Wrapping

wrap surrounds a block's content with a prefix and suffix. The suffix is drawn in the style that was active before the block, even if the block changed it, including a style chosen by switch_style.

Tmux.format do
  switch_style(Tmux.pane_input_off => {fg: :red}, else: {fg: :blue})
  # Yellow "session:window.pane", with brackets in the selected color.
  wrap "[", "]" do
    style fg: :yellow
    text "#{Tmux.session_name}:#{Tmux.window_index}."
    # Highlight only the pane number while the prefix is held.
    if?(Tmux.client_prefix) { style fg: :white }
    append Tmux.pane_index
  end
  # A template lambda receives a placeholder for the green command name.
  wrap ->(content) { " (#{content}) " } do
    style fg: :green
    append Tmux.pane_current_command
  end
end

Screenshot: this format in the status line

Powerline helpers

Flags, segments, and chips draw Powerline-style blocks with their edge glyphs and color transitions. Their content can be a string (with interpolated expressions), an expression, or an array mixing the two; a block draws custom content instead.

left_segment / right_segment: adjoining blocks with one pointed edge. left_segment draws its edge over the previous block's background automatically. For right_segment, set over: to the next block's background to join the blocks without gaps.
left_flag / right_flag: a self-contained badge, pointed at one end and notched at the other. over: sets the background behind the point; notch_over: can set a different background for the notch. If omitted, the notch uses the same background as the point.
chip: a floating block with an edge on each side. When both edges are thin, bg: colors the outline and text, and over: sets the shared background behind the edges and content (default :default). fg: sets the text color for chips with solid edges.
p: sets the padding spaces on each side (default 1); attrs: styles the content.
left: and right: choose a chip's edge shapes: :triangle (the default), :thin, :round, :round_thin, :rslant (/), or :lslant (\). The keyword supplies the side, so left: :round, right: :round makes a rounded chip. Using the same slant on both sides makes a parallelogram; the two slants can also be mixed.
glyph: accepts the same shapes for flags and segments, using the helper's left_ or right_ direction. Exact names from Tmux::Glyph and literal glyph strings are also accepted when you want a specific character.

left_ helpers point left, for the right side of the status line; right_ helpers point right, for the left side:

# status-right: blocks chained from right to left.
Tmux.format do
  # Path (with the home directory shortened to ~), then command; each edge
  # is drawn over the previous block's color.
  left_segment Tmux.pane_current_path.substitute("^#{Dir.home}", "~"), bg: :colour236, fg: :white
  left_segment Tmux.pane_current_command, bg: :colour238, fg: :white
end

Screenshot: this format as status-right

# status-left: blocks chained from left to right.
Tmux.format do
  # Each edge sits over the next block's background for a continuous chain.
  right_segment Tmux.session_name, bg: :blue, fg: :black, over: :colour238
  # Content as a keyword, with its padding supplied by the string.
  right_segment content: " #{Tmux.window_index} ", bg: :colour238, fg: :white, p: 0, over: :colour236
  # The final edge meets the default background; only the text is italic.
  right_flag(bg: :colour236, fg: :white, over: :default, attrs: :italics, close: false) do
    text " #{Tmux.host_short} "
  end
end

Screenshot: this format as status-left

Tmux.format do
  # A chip with the default triangle edges...
  chip "default", bg: :blue, fg: :black
  text " "
  # ...rounded edges...
  chip "round", bg: :magenta, fg: :black, left: :round, right: :round
  text " "
  # ...thin edges and cyan text, all on the default background...
  chip "thin", bg: :cyan, fg: :black, left: :thin, right: :thin
  text " "
  # ...and slants leaning right or left, with the side inferred for each edge.
  chip "rslant", bg: :yellow, fg: :black, left: :rslant, right: :rslant
  text " "
  chip "lslant", bg: :green, fg: :black, left: :lslant, right: :lslant
end

Screenshot: these chips in the status line

Zones

Tmux.pane_border builds a format from left, centre, and right zones, in that order whatever order they are defined in. Each zone is an ordinary format block.

Tmux.configure do
  global.status = false
  # Heavy pane borders with a label along the top, the active one in blue.
  window.pane.border.status = :top
  window.pane.border.lines = :heavy
  window.pane.border.style = {fg: "#45475a"}
  window.pane.active_border.style = {fg: "#89b4fa"}

  active = Tmux.pane_active
  accent = switch(active => "#89b4fa", else: "#45475a")
  window.pane.border.format = Tmux.pane_border do
    # The command and directory on the left, brighter on the active pane...
    left do
      style(fg: switch(active => "#cdd6f4", else: "#7f849c"), p: 1) do
        text "#{Tmux.pane_current_command} #{Tmux.pane_current_path.substitute("^#{Dir.home}", "~")}"
      end
    end
    # ...the window name in the middle...
    center { append " #{Tmux.window_name} "}
    # ...and the pane number as a chip on the right.
    right { chip Tmux.pane_index, bg: accent, fg: "#11111b", left: :round, right: :round, p: 0 }
  end
end

Screenshot: two panes with these borders

Expanding options

expand_option inserts a user option's value and expands it as a format, for segments that a plugin or script maintains. Spell user-option names with tmux's @ prefix: :@my_plugin_segment as a Ruby symbol, or "@my_plugin_segment" as a string. The same spelling works for Tmux.user_option expressions and scoped assignments such as global[:@my_plugin_segment] = "...".

Tmux.format do
  # Whatever format string a plugin keeps in @my_plugin_segment.
  expand_option :@my_plugin_segment
end

Expressions and conditions

Expressions represent tmux values that are evaluated when tmux uses them. Use them as conditions in both configuration and format blocks, interpolate them into text, or pass them to append, style, and the Powerline helpers.

Tmux.format do
  # Built-in variables: client_prefix, pane_active, pane_current_command,
  # pane_current_path, pane_in_mode, pane_index, pane_input_off, pane_mode,
  # pane_synchronized, window_index, window_name, window_zoomed_flag,
  # session_name, host, host_short.
  text "#{Tmux.session_name} "
  # Any other tmux variable by name.
  text "#{Tmux.variable(:window_panes)} "
  # A user option (@attn_state).
  if?(Tmux.user_option(:@attn_state)) { text "!" }
  # Raw tmux format code as an expression.
  text Tmux.raw("\#{t:session_created}")
end

Use >, <, >=, and <= for numeric comparisons, and == / != for string comparisons. Put the expression on the left of the operator; literal operands are escaped for you:

command = Tmux.pane_current_command

Tmux.format do
  # String comparison.
  if?(command == "vim") { text "editing" }
  if?(command != "zsh") { text "busy" }

  # Numeric comparison.
  if?(Tmux.pane_index > 9) { text "more than 9" }
  if?(Tmux.pane_index < 2) { text "fewer than 2" }
  if?(Tmux.pane_index >= 10) { text "10 or more" }
  if?(Tmux.pane_index <= 1) { text "1 or fewer" }

  # Regular-expression match.
  if?(command.matches("^(bash|zsh|fish)$")) { text "shell" }

  # Regular-expression substitution: shorten the home directory to "~/".
  text Tmux.pane_current_path.substitute("^#{Dir.home}/", "~/")
end

substitute does not accept : in its pattern or replacement.

Combining conditions

Write && / || directly in if?, .elsif?, or Tmux.if? conditions, or in inline switch / switch_style condition keys. Use ! to negate an expression. Comparisons bind more tightly than && / ||, and parentheses work as in ordinary Ruby:

active = Tmux.pane_active

Tmux.format do
  if?(active && Tmux.client_prefix) { text "prefix" }
    .elsif?(active && Tmux.pane_in_mode) { text "copy mode" }
    .else { text "normal" }

  style fg: switch(active && Tmux.client_prefix => :red, else: :white)
end

Use tmux expressions as logical operands, not Ruby booleans or nil. Keep conditions to a single expression, without assignments, control flow, or nested blocks. To reuse conditional content, build a Tmux.if? format.

&& / || require configuration files run through the CLI or Tmux.load_file, not plain Ruby require, load, or direct library calls. Put combined conditions directly in the calls above, not in intermediate assignments such as combined = active && Tmux.client_prefix. Use if?, not Ruby's if, for conditions that depend on tmux state.

Configuration DSL

Inside Tmux.configure, statements apply in the order they are written.

Options by name

global (session options), window (window and pane options), and server support every built-in option available in the target tmux version, each in its proper scope. Unknown names and settings in the wrong scope raise errors. Use underscores for native dashes, group related names with dots, or use the exact native name in brackets. These spellings are interchangeable and use the same validation, as the equivalent assignments below show. Assigning sets an option, << appends to it, and unset reverts it to its inherited value. Style options also accept a hash.

Tmux.configure do
  # Three equivalent ways to set status-interval.
  global.status_interval = 5        # set-option -g status-interval 5
  global.status.interval = 5        # set-option -g status-interval 5
  global[:"status-interval"] = 5    # set-option -g status-interval 5

  # Session options.
  global.prefix = "C-s"              # set-option -g prefix "C-s"
  global.prefix2 = "C-a"             # set-option -g prefix2 "C-a"
  global.base_index = 1              # set-option -g base-index 1
  global.status.position = :top      # set-option -g status-position "top"

  # A style option, written as a hash.
  global.status.style = {bg: :default, fg: :white} # set-option -g status-style "bg=default,fg=white"

  # Window and pane options.
  window.mode_keys = :vi             # set-option -gw mode-keys "vi"

  # The same flexibility applies to pane-border-lines.
  window.pane_border_lines = :heavy  # set-option -gw pane-border-lines "heavy"
  window.pane.border.lines = :heavy  # set-option -gw pane-border-lines "heavy"
  window[:"pane-border-lines"] = :heavy # set-option -gw pane-border-lines "heavy"

  # Server options; << appends (set-option -a).
  server.escape_time = 0             # set-option -s escape-time 0
  server.terminal_features << ",*:RGB" # set-option -sa terminal-features ",*:RGB"

  # Revert to the inherited value.
  window.status.bell_style.unset     # set-option -gwu window-status-bell-style
end

Native names, custom options, and arrays

Bracket notation accepts native option names with the same validation. Use it for custom @ options, whose names you or a plugin define. Integer indices select elements of tmux array options.

Tmux.configure do
  # Brackets demonstrate an exact native name; global.status_interval = 5 is equivalent.
  global[:"status-interval"] = 5    # set-option -g status-interval 5
  window.monitor_bell = true        # set-option -gw monitor-bell on
  server.exit_empty = false         # set-option -s exit-empty off

  # Custom options use their native @ names, in whichever scope you need.
  global[:@my_plugin_color] = "colour37" # set-option -g @my_plugin_color "colour37"
  window[:@my_plugin_segment] = "!"     # set-option -gw @my_plugin_segment "!"

  # A custom terminal key sequence in an array option.
  server.user_keys[0] = "\033[5;30012~" # set-option -s user-keys[0] "\033[5;30012~"

  # Append to the current value.
  global.update_environment << "MY_VAR" # set-option -ga update-environment "MY_VAR"

  # Revert an option.
  global.status.right.unset         # set-option -gu status-right
end

Format-valued options

Assign a Tmux.format wherever an option takes a format string:

Tmux.configure do
  # An option whose value is a format...
  # set-option -g status-left " #{session_name} "
  global.status.left = Tmux.format do
    text " #{Tmux.session_name} "
  end

  # ...and a window option whose value is a format.
  # set-option -gw window-status-format " #{window_index}:#{window_name} "
  window.status.format = Tmux.format do
    text " #{Tmux.window_index}:#{Tmux.window_name} "
  end
end

Variable expansion

When tmux loads the configuration it expands $NAME (a name starting with a letter or _) and a leading ~ in option values, just as in hand-written configuration. expand: false keeps a value literal until a shell or a #(...) command sees it. Use an option's set method to pass expand: false or append: true alongside its value.

Tmux.configure do
  # tmux stores your home directory here, expanded when the file loads.
  global[:@home] = "$HOME" # set-option -g @home "$HOME"

  # Stored literally, as "~/bin/$COMMAND".
  global[:@literal_path].set("~/bin/$COMMAND", expand: false) # set-option -g @literal_path "\~/bin/\$COMMAND"

  # The shell, not tmux, expands $HOME each time the command runs.
  # set-option -g status-right "#([ -f \$HOME/.name ] && cat \$HOME/.name || hostname)"
  global.status.right.set(Tmux.format do
    command '[ -f $HOME/.name ] && cat $HOME/.name || hostname'
  end, expand: false)
end

Environment, sourcing, and shell commands

Tmux.configure do
  # A global environment variable for new panes.
  environment "EDITOR", "nvim"

  # Load another tmux file; quiet: true skips a missing one without an error.
  source "~/.tmux.local.conf", quiet: true

  # Run a shell command while the file loads (background: true for -b).
  run_shell "~/.tmux/plugins/tpm/tpm", background: true
end

Key bindings

bind maps a key to commands. Name the commands in a chain, write a block of commands, or pass a tmux command string. table: picks a key table, no_prefix: true binds without the prefix (-n), repeat: true allows repeating (-r), and note: adds a description (-N). unbind removes a binding.

Given only a key, bind returns a chain. Each method adds a command, and cwd sets the directory for the split or new_window before it:

Tmux.configure do
  # tmux: bind-key "-" split-window -v -c "#{pane_current_path}"
  bind("-").split(:vertical).cwd(:current)

  # tmux: bind-key "|" split-window -h -l "30%" -c "~/src"
  bind("|").split(:horizontal, size: "30%", cwd: "~/src")

  # tmux: bind-key "c" new-window
  bind("c").new_window

  # Commands run in order: a named window, then back to the last pane.
  # tmux: bind-key "C" new-window -n "scratch" -c "#{pane_current_path}" \; select-pane -t "{last}"
  bind("C").new_window(name: "scratch").cwd(:current).select_pane(target: "{last}")

  # tmux: bind-key -r "h" select-pane -L
  bind("h", repeat: true).select_pane(:left)

  # tmux: bind-key -r "<" resize-pane -L 10
  bind("<", repeat: true).resize_pane(:left, 10)

  # tmux: bind-key -n "M-z" resize-pane -Z
  bind("M-z", no_prefix: true).zoom

  # tmux: bind-key "r" source-file "~/.tmux.conf" \; display-message "Reloaded"
  bind("r").source("~/.tmux.conf").display_message("Reloaded")
end

split takes tmux's direction names: :vertical (-v) puts the new pane below, and :horizontal (-h) puts it to the right. :v and :h are shorthand for them. Pane directions are :left, :right, :up, and :down. The named commands are split, new_window, select_pane, resize_pane, zoom, kill_pane, kill_window, source, display_message, display_menu, copy_mode, and load_config. Use command for any other tmux command (its arguments are quoted for you) and raw for a command written exactly as tmux expects it.

The block form uses the same methods, one command per line, so cwd on its own line applies to the split above it:

Tmux.configure do
  # tmux: bind-key "|" split-window -h -c "some-dir"
  bind "|" do
    split :h # or :horizontal
    cwd "some-dir"
  end

  # tmux: bind-key "C" new-window -n "scratch" -c "#{pane_current_path}" \; select-pane -t "{last}"
  bind "C" do
    new_window name: "scratch"
    cwd :current
    select_pane target: "{last}"
  end
end

Command strings pass through as written:

Tmux.configure do
  # A command string.
  # tmux: bind-key "|" split-window -h -c "#{pane_current_path}"
  bind "|", %q{split-window -h -c "#{pane_current_path}"}

  # Repeatable, so prefix + < < < resizes three times.
  # tmux: bind-key -r "<" resize-pane -L 10
  bind "<", "resize-pane -L 10", repeat: true

  # Without the prefix, with a description for list-keys -N.
  # tmux: bind-key -n -N "Zoom the pane" "M-z" resize-pane -Z
  bind "M-z", "resize-pane -Z", no_prefix: true, note: "Zoom the pane"

  # A block in the copy-mode-vi key table.
  # tmux: bind-key -T "copy-mode-vi" "WheelUpPane" select-pane \; send-keys -t "{mouse}" -X clear-selection \; send-keys -t "{mouse}" -X -N 5 scroll-up
  bind "WheelUpPane", table: "copy-mode-vi" do
    # Select the pane under the mouse...
    select_pane

    # ...then send copy-mode commands to it.
    copy_mode :clear_selection, target: "{mouse}"
    copy_mode :scroll_up, target: "{mouse}", count: 5
  end

  # Remove the default prefix binding, a root-table binding, and a
  # copy-mode one.
  # tmux: unbind-key "C-b"
  unbind "C-b"

  # tmux: unbind-key -n "M-z"
  unbind "M-z", no_prefix: true

  # tmux: unbind-key -T "copy-mode-vi" "v"
  unbind "v", table: "copy-mode-vi"
end

Blocks suit longer bindings, such as a menu or a command with no named helper:

Tmux.configure do
  # tmux: bind-key "m" display-menu -T "Layout" "Tiled" "t" "select-layout tiled" "" "Even horizontal" "h" "select-layout \"even-horizontal\" \\; display-message \"Layout: even horizontal\""
  bind "m" do
    # A menu titled "Layout"; each item runs a command or a command block.
    display_menu title: "Layout" do
      item "Tiled", key: "t", command: "select-layout tiled"
      separator
      item "Even horizontal", key: "h" do
        command :select_layout, "even-horizontal"
        display_message "Layout: even horizontal"
      end
    end
  end

  # Any command, with quoted arguments.
  # tmux: bind-key "S" swap-pane "-s" "{last}" \; select-pane -t "{last}"
  bind "S" do
    command :swap_pane, "-s", "{last}"
    select_pane target: "{last}"
  end

  # raw adds a command exactly as written.
  # tmux: bind-key "X" confirm-before -p 'kill window? (y/n)' kill-window
  bind "X" do
    raw "confirm-before -p 'kill window? (y/n)' kill-window"
  end
end

commands builds a command sequence outside a binding, so helper methods can return one and several bindings can share it:

Tmux.configure do
  def split_here(direction)
    commands do
      split direction, cwd: :current
      display_message "split"
    end
  end

  # tmux: bind-key "|" split-window -h -c "#{pane_current_path}" \; display-message "split"
  bind "|", split_here(:horizontal)

  # tmux: bind-key "-" split-window -v -c "#{pane_current_path}" \; display-message "split"
  bind "-", split_here(:vertical)
end

Reloading from Ruby

load_config returns commands that recompile a Ruby configuration and load it, for use with bind. The binding passes the running server's socket, so it reloads the server whose key was pressed.

Tmux.configure do
  # A helper method, reusable in this configuration.
  def reload_config
    load_config __FILE__, message: "tmux reloaded"
  end

  # prefix + r recompiles this file and loads it.
  bind "r", reload_config

  # executable: names the tmux.rb to run, e.g. one outside $PATH.
  bind "R", load_config(__FILE__, executable: File.expand_path("~/bin/tmux.rb"))
end

Conditional configuration

Use the same conditional chain as in format blocks to choose which configuration commands tmux runs. Pass a tmux expression directly, or use shell("command") to check whether a shell command exits successfully. Shell checks run when tmux applies the configuration. Later branches are checked only if the earlier ones fail. Use Tmux.shell(...) to define a reusable check outside a configuration block.

Use shell("command", background: true) to let tmux continue without waiting for the check. For an existing native format string, use Tmux.raw('...') as the condition; if?(expression, background: true) also supports tmux's background flag. Shell checks can be used in configuration conditionals; format blocks use tmux expressions.

tmux_from and tmux_below apply configuration on tmux at least, or older than, a "major.minor" version, based on the running server's version.

Tmux.configure do
  # Choose the first available clipboard tool.
  if?(shell("command -v pbcopy")) do
    global[:@yank_command] = "pbcopy" # set-option -g @yank_command "pbcopy"
  end.elsif?(shell("command -v wl-copy")) do
    global[:@yank_command] = "wl-copy" # set-option -g @yank_command "wl-copy"
  end.else do
    global[:@yank_command] = "xclip -selection clipboard" # set-option -g @yank_command "xclip -selection clipboard"
  end

  # Choose a style based on the shell environment.
  if?(shell('test -n "$SSH_CONNECTION"')) do
    global.status.style = "bg=colour52" # set-option -g status-style "bg=colour52"
  end.else do
    global.status.style = "bg=colour236" # set-option -g status-style "bg=colour236"
  end

  # A format condition instead of a shell command.
  if?(Tmux.host_short == "laptop") do
    global.status.style = "bg=colour22" # set-option -g status-style "bg=colour22"
  end

  # Don't wait for a slow check while tmux starts.
  if?(shell("command -v slow-check", background: true)) do
    global[:@slow_check] = "yes" # set-option -g @slow_check "yes"
  end

  # Only on tmux 3.2 or newer...
  tmux_from "3.2" do
    server.extended_keys = :on # set-option -s extended-keys "on"
  end

  # ...and a fallback for older versions, with .else for the rest.
  tmux_below "3.0" do
    global.status.style = "bg=black" # set-option -g status-style "bg=black"
  end.else do
    global.status.style = "bg=terminal" # set-option -g status-style "bg=terminal"
  end
end

Comments and hooks

comment writes # lines into the generated file, for whoever reads or edits it. hook sets a tmux hook from a command string or a block of commands, as bind does; index: gives it its own slot so setting it again replaces that slot rather than adding a copy, and scope: picks :global (session hooks), :window, or :pane.

Tmux.configure do
  # # Snapshot sessions whenever one closes.
  comment "Snapshot sessions whenever one closes."

  # tmux: set-hook -g "session-closed[100]" "run-shell -b \"save-sessions\""
  hook "session-closed", %q{run-shell -b "save-sessions"}, index: 100

  # tmux: set-hook -gw "pane-focus-in" "display-message \"focused\""
  hook("pane-focus-in", scope: :window) { display_message "focused" }
end

Raw commands and composition

raw passes tmux commands through verbatim (one per line; a trailing \ continues a line), and blank adds an empty line. append includes another configuration's statements, and use accepts any object that responds to to_config, such as a plugin's Ruby package.

shared = Tmux.configure { global.history_limit = 50_000 } # set-option -g history-limit 50000

# Anything with a to_config method can be used.
clipboard = Object.new
def clipboard.to_config = Tmux.configure { server.set_clipboard = :external } # set-option -s set-clipboard "external"

Tmux.configure do
  # Verbatim tmux commands, including a continued line.
  raw "set-option -g display-time 2000"
  raw "bind-key T \\\n  clock-mode"
  blank

  # Another configuration's statements, in place.
  append shared
  use clipboard
end

Development

bundle install
bundle exec rake test

bundle exec rake test uses the tmux on your PATH. bundle exec rake test:tmux builds each tmux version CI tests (3.2a, the newest release of each later minor version, and the development branch) from source into tmp/tmux and runs the suite against each; set VERSIONS="3.2a 3.8" to pick some. Building needs a C compiler, bison, pkg-config, and the libevent and ncurses headers.

The suite starts throwaway tmux servers on sockets in temporary directories and never touches your running server. Tests that need tmux are skipped when it is not installed, except on CI, where they fail. After an intended change to the author config's output, regenerate its fixture with UPDATE_FIXTURES=1 bundle exec rake test and review the diff.

The README screenshots are regenerated from real tmux sessions with bundle exec rake screenshots; see docs/screenshots.

Build the gem with bundle exec rake build (into pkg/), and publish with bundle exec rake release.

License

MIT. See LICENSE. The ported configurations in examples/popular_configs keep their upstream licenses beside them.

Name		Name	Last commit message	Last commit date
.github/workflows		.github/workflows
bin		bin
docs		docs
examples		examples
lib		lib
script		script
test		test
.gitignore		.gitignore
CHANGELOG.md		CHANGELOG.md
Gemfile		Gemfile
LICENSE		LICENSE
README.md		README.md
Rakefile		Rakefile
VISION.md		VISION.md
tmux.gemspec		tmux.gemspec

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