Bash – Tmux – Get number of panes in the current window in bash variable

tmux (since v1.5) provides TMUX_PANE in the environment of the process it launches for a pane; each new pane gets a server-unique value. So, assuming that TMUX_PANE is available in your environment, then this should do what I think you want:

tmux display -pt "${TMUX_PANE:?}" '#{pane_index}'

The ${…:?} syntax in a Bourne-like shell prevents the expansion of missing or empty parameters. In this case, an empty expansion would fall back to the default of using “the currently active pane”, which is usually—but not always—the same as “this pane” (they will likely differ if the command’s tty is not the one that tmux started; e.g. because of using script or expect, et cetera).

The following worked for me.

To ~/.bashrc, add the line:

PS1='$([ -n "$TMUX" ] && tmux setenv TMUXPWD_$(tmux display -p "#I") $PWD)\u@\H:\w$ '

And to ~/.tmux.conf, add the lines:

bind-key c run-shell 'tmux neww "cd $(tmux display -p "\$TMUXPWD_#I"); exec bash"'
bind-key % run-shell 'tmux splitw -h "cd $(tmux display -p "\$TMUXPWD_#I"); exec bash"'
bind-key '"' run-shell 'tmux splitw -v "cd $(tmux display -p "\$TMUXPWD_#I"); exec bash"'

Restart tmux.

Sources

See the section, "How can I open a new window in the same directory as the current window?" at http://tmux.svn.sourceforge.net/viewvc/tmux/trunk/FAQ.

Note that the characters at the end of the .bashrc line had to be changed from the original at the link above to '\u@\H:\w$ ' in order to properly display the complete bash prompt. See http://www.tldp.org/HOWTO/Bash-Prompt-HOWTO/bash-prompt-escape-sequences.html for more info.