run-shell overrides $SHELL which causes broken default-command on mac

[von]

As described in tmux-plugins/tpm#295 and tmux/tmux#4166, run-shell is now setting $SHELL to sh which causes tmux-sensible, at line 103, to incorrectly set default-command to use 'sh' instead of the user-selected shell. This means new panes and windows will fire up with sh instead of what the user expects (e.g., zsh).

A work around is to put set -g default-command "reattach-to-user-namespace -l $SHELL" directly into ones .tmux.conf to override tmux-sensible.

One possible fix would seem to be to modify tmux-sensible to use the tmux default-shell variable instead of $SHELL.

Or see this comment for other suggested fixes.

[venlinz]

I've also faced this issue, I have analyzed this further more, here are my thoughts on fixing this issue,

• removing reattach-to-user-namespace would cause breakage for people using tmux < 2.6
• the default-shell variable may or may not be set by the user so relying on it can cause problems.
• using tmux showenv -g SHELL will use the system default global $SHELL variable and this overrides the tmux configured default-shell variable, if setting default-shell in tmux config doesn't update the$SHELL variable accordingly, this will load default shell from system's $SHELL variable.

A fault tolerant solution would be to use default-shell variable if it is set, otherwise use tmux showenv -g SHELL as a fallback instead of using $SHELL variable directly.

@bruno- @von please share your opinions on this,
I would love to create a PR implementing this, if it is ok.

[von]

That seems reasonable. FYI, as I read the current tmux manpage, default-shell is set by tmux from $SHELL automatically on start-up and does not need to be set by the user's configuration. That matches the behavior I'm seeing (i.e. it is set and I didn't do it).