Checklist

• I have read through the manual page (man fzf)
• I have searched through the existing issues
• For bug reports, I have checked if the bug is reproducible in the latest version of fzf

Output of fzf --version

0.61.2 (AlpineLinux)

OS

• Linux
• macOS
• Windows
• Etc.

Shell

• bash
• zsh
• fish

Problem / Steps to reproduce

Since upgrading to v0.61.2, tmux run-shell 'fzf --tmux' returns

'fzf --tmux' returned 2

This works with v0.61.1

Bisecting leads to af8fe91 (#4351), which checks for TMUX_PANE to be present. But it appears that variable is not available in tmux run-shell either:

 tmux run-shell 'printenv TMUX_PANE'                                                                                                                                                                           
'printenv TMUX_PANE' returned 1

So this change breaks my tmux setup, which does:

bind -n C-f run-shell -b "tmux list-sessions -F \"##S\" | fzf --tmux bottom,15 | xargs -r tmux switch-client -t"

Reverting that commit makes that binding work again. Another workaround would be to explicitly define TMUX_PANE to something in that binding, but that seems to be more of a hack.