Overview
Format strings allow you to customize the output of many tmux commands and the appearance of the status line. Variables are enclosed in #{ and } and are replaced with their values.
Basic Syntax
# Simple variable
#{session_name}
# Multiple variables
#{session_name}:#{window_index}.#{pane_index}
# In commands
list-sessions -F "Session: #{session_name}"
display-message "Current window: #{window_name}"
Special Characters
Replaced by a , (use inside conditionals to escape commas)
Replaced by a } (use inside conditionals to escape closing braces)
Single-Character Aliases
Some common variables have short aliases:
#S → #{session_name}#W → #{window_name}#I → #{window_index}#P → #{pane_index}#D → #{pane_id}#F → #{window_flags}#T → #{pane_title}#H → #{host}#h → #{host_short}
Conditionals
Conditionals use the ? prefix and allow branching based on variable values.
Basic Conditional
#{?session_attached,attached,not attached}
session_attached is non-zero, shows “attached”, otherwise “not attached”.
With Default
#{?window_zoomed_flag,ZOOMED,}
Nested Conditionals
#{?pane_in_mode,#[fg=yellow],#{?synchronize-panes,#[fg=red],#[fg=green]}}MODE
Multiple Conditions
#{?session_format,session,window_format,window,pane}
Escaping Inside Conditionals
Inside conditionals, use #, for comma and #} for closing brace:
#{?pane_in_mode,#[fg=white#,bg=red],#[fg=red#,bg=white]}#W
Comparisons
String Comparisons
# Equality
#{==:#{host},myhost}
# Inequality
#{!=:#{session_name},default}
# Less than
#{<:#{window_index},5}
# Greater than
#{>:#{pane_width},80}
# Less than or equal
#{<=:#{window_panes},4}
# Greater than or equal
#{>=:#{session_windows},2}
1 if true, 0 if false.
Logical Operators
# OR
#{||:#{pane_in_mode},#{alternate_on}}
# AND
#{&&:#{session_attached},#{window_active}}
# NOT
#{!:#{pane_in_mode}}
# Double NOT (convert to canonical boolean)
#{!!:#{window_name}}
Pattern Matching
Glob Pattern
# Default: glob pattern
#{m:*foo*,#{host}}
# Case-insensitive glob
#{m/i:*foo*,#{host}}
Regular Expression
# Regex match
#{m/r:^[0-9]+$,#{window_index}}
# Case-insensitive regex
#{m/ri:^A,#{window_name}}
Content Search
# Search pane content
#{C:Error}
# Regex search
#{C/r:^ERROR:}
# Case-insensitive
#{C/ri:warning}
Numeric Operations
Prefix with e and an operator:
Arithmetic
# Addition
#{e|+:5,3} # → 8
# Subtraction
#{e|-:10,3} # → 7
# Multiplication
#{e|*:4,5} # → 20
# Division
#{e|/:15,3} # → 5
# Modulus
#{e|m:10,3} # → 1
#{e|%:10,3} # → 1
Floating Point
Add f flag for floating point operations:
# Floating point multiplication with 4 decimal places
#{e|*|f|4:5.5,3} # → 16.5000
# Floating point division
#{e|/|f|2:10,3} # → 3.33
Numeric Comparisons
#{e|==:#{window_panes},1} # → 1 if one pane
#{e|>:#{pane_width},80} # → 1 if width > 80
String Manipulation
Length
# Character count
#{n:window_name}
# Display width
#{w:window_name}
Truncation
# First 10 characters
#{=10:pane_title}
# Last 10 characters
#{=-10:pane_title}
# With ellipsis suffix
#{=/10/...:pane_title}
# With ellipsis prefix
#{=-10/.../p:pane_title}
Padding
# Pad to 10 characters (left padding)
#{p10:window_name}
# Pad right
#{p-10:window_name}
Repetition
# Repeat string 5 times
#{R:=,5} # → =====
# Repeat with format
#{R:#{window_name},3}
Case Conversion
# Basename
#{b:pane_current_path}
# Dirname
#{d:pane_current_path}
Quoting
# Shell quote
#{q:window_name}
# Quote hash characters
#{q/h:window_name} # # becomes ##
Substitution
# Replace foo with bar
#{s/foo/bar/:window_name}
# Regex substitution
#{s/([0-9]+)/NUM/r:window_name}
# Case-insensitive
#{s/foo/bar/i:window_name}
# Use different delimiter
#{s|/tmp/|/var/|:pane_current_path}
Convert to String
# Default format
#{t:window_activity} # → Sun Oct 25 09:25:02 2015
# Short format for past times
#{t/p:window_activity}
strftime format (escape % as %% if needed):
#{t/f/%%H#:%%M:window_activity} # → 09:25
#{t/f/%%Y-%%m-%%d:session_created} # → 2015-10-25
Character Conversion
# ASCII to character
#{a:65} # → A
#{a:97} # → a
# Color to hex
#{c:blue} # → #0000ff
Expansion
Single Expansion
# Expand format in variable
#{E:status-left}
Double Expansion with strftime
# Expand and process time formats
#{T:status-left}
Literal
# Don't expand
#{l:#{?pane_in_mode,yes,no}} # → #{?pane_in_mode,yes,no}
Loops
Loop Over Items
# Loop sessions
#{S:#{session_name} }
# Loop windows
#{W:#{window_index}:#{window_name} }
# Loop panes
#{P:#{pane_index} }
# Loop clients
#{L:#{client_name} }
With Sort Order
# Sort by index
#{S/i:#{session_name} }
# Sort by name
#{W/n:#{window_name} }
# Sort by activity time
#{S/t:#{session_name} }
# Reverse sort
#{W/r:#{window_index} }
#{W:#{window_name},#[fg=red]#{window_name}}
Check Existence
# Check window exists
#{N/w:mywindow} # → 1 if exists
# Check session exists
#{N/s:mysession} # → 1 if exists
Session Variables
#{session_name} (alias: #S): Name of session#{session_id}: Unique session ID (1,2, etc.)#{session_created}: Time session created#{session_activity}: Time of last activity#{session_attached}: Number of clients attached#{session_windows}: Number of windows#{session_group}: Name of session group#{session_grouped}: 1 if session in a group
Window Variables
#{window_name} (alias: #W): Name of window#{window_index} (alias: #I): Index of window#{window_id}: Unique window ID (@1, @2, etc.)#{window_active}: 1 if window is active#{window_flags} (alias: #F): Window flags#{window_panes}: Number of panes in window#{window_width}, #{window_height}: Window dimensions#{window_layout}: Layout description#{window_zoomed_flag}: 1 if window is zoomed
Pane Variables
#{pane_id} (alias: #D): Unique pane ID (%1, %2, etc.)#{pane_index} (alias: #P): Index of pane#{pane_title} (alias: #T): Title of pane#{pane_current_path}: Current working directory#{pane_current_command}: Current command#{pane_width}, #{pane_height}: Pane dimensions#{pane_active}: 1 if active pane#{pane_in_mode}: Number of modes pane is in#{pane_pid}: PID of first process in pane#{pane_tty}: Pseudo terminal of pane
Client Variables
#{client_name}: Name of client#{client_tty}: Pseudo terminal of client#{client_width}, #{client_height}: Client dimensions#{client_session}: Name of attached session#{client_created}: Time client created#{client_activity}: Time of last activity#{client_prefix}: 1 if prefix key pressed#{client_readonly}: 1 if client is read-only
Server Variables
#{host} (alias: #H): Hostname#{host_short} (alias: #h): Hostname without domain#{pid}: Server PID#{socket_path}: Server socket path#{start_time}: Server start time#{version}: Server version#{server_sessions}: Number of sessions
Buffer Variables
#{buffer_name}: Name of buffer#{buffer_size}: Size in bytes#{buffer_created}: Time created#{buffer_sample}: Sample of buffer content
Other Variables
#{cursor_x}, #{cursor_y}: Cursor position#{scroll_region_upper}, #{scroll_region_lower}: Scroll region#{alternate_on}: 1 if alternate screen is on#{history_size}: Number of lines in history#{history_limit}: Maximum history lines#{copy_cursor_x}, #{copy_cursor_y}: Copy mode cursor#{selection_present}: 1 if selection in copy mode
Practical Examples
Status Line
# Session info with colors
set -g status-left "#[fg=green]#S #[fg=yellow]#I:#P"
# Right status with conditionals
set -g status-right "#{?client_prefix,#[fg=red],#[fg=green]}#{host_short}"
# Window status
set -g window-status-format "#I:#W#{?window_flags,#{window_flags}, }"
set -g window-status-current-format "#[fg=red]#I:#W#F"
# Custom session list
list-sessions -F "#{session_name}: #{session_windows} windows, #{session_attached} clients"
# Window list with activity
list-windows -F "#I: #W #{?window_activity_flag,(active),}"
# Pane info
list-panes -F "Pane #P: #{pane_current_command} in #{pane_current_path}"
Conditional Logic
# Show different info based on context
display-message "Status: #{?session_attached,Attached,Detached} #{?window_zoomed_flag,- Zoomed,}"
# Dynamic colors
set -g status-style "bg=#{?client_prefix,red,green}"
# Truncate and pad window name
set -g window-status-format "#{=/10/...:window_name}#{p-15:pane_title}"
# Count and display
set -g status-right "#{E:#{e|+:#{window_panes},0}} panes"