Tmux environment variables

The user configuration file for the tmux terminal multiplexer, .tmux.conf, supports defining and using environment variables in the configuration, with the same syntax as most shell script languages:

set-option -g default-terminal $TERM

This can be useful for any case in which it may be desirable to customise the shell environment when inside tmux, beyond setting variables like default-terminal. However, if you repeat yourself in places in your configuration file, it can also be handy to use them as named constants. An example could be establishing colour schemes:


set-window-option -g window-status-activity-bg $TMUX_COLOUR_BORDER
set-window-option -g window-status-activity-fg $TMUX_COLOUR_ACTIVE
set-window-option -g window-status-current-format "#[fg=$TMUX_COLOUR_ACTIVE]#I:#W#F"
set-window-option -g window-status-format "#[fg=$TMUX_COLOUR_INACTIVE]#I:#W#F"

The explicit commands to work with environment variables in .tmux.conf are update-environment, set-environment, and show-environment, and are featured in the manual.

Reloading tmux config

If you have made changes to your tmux configuration file in the ~/.tmux.conf file, it shouldn’t be necessary to start the server up again from scratch with kill-server. Instead, you can prompt the current tmux session to reload the configuration with the source-file command.

This can be done either from within tmux, by pressing Ctrl+B and then : to bring up a command prompt, and typing:

:source-file ~/.tmux.conf

Or simply from a shell:

$ tmux source-file ~/.tmux.conf

This should apply your changes to the running tmux server without affecting the sessions or windows within them.