set is the alias of set-option.
set -g is used to set global options and -ga appends values to existing settings.
From Tmux’s man page:
With -a, and if the option expects a string or a style, value is
appended to the existing setting. For example:set -g status-left "foo" set -ag status-left "bar"Will result in ‘foobar’. And:
set -g status-style "bg=red" set -ag status-style "fg=blue"Will result in a red background and blue foreground. Without -a, the
result would be the default background and a blue foreground.
set-window-option (alias setw) is used to configure window options (allow-rename, mode-keys, synchronize-panes, etc.) and the same flag options are available.
See:
- https://linux.die.net/man/1/tmux
- https://superuser.com/questions/758843/difference-between-global-server-session-and-window-options