How to set and use variable in tmux.conf depending on whether an environment variable is set

Question

(Disclaimer: I am fully aware that there are solutions to the problem I describe below that involve writing and calling shell scripts that interact with a running tmux server, o

Answer 1

Also you can use display -p to print formats. In master and 2.9 you can add -v to see how they are parsed:

$ tmux setenv -g FOO bar
$ tmux display -pv '#{==:#{FOO},baz}'
# expanding format: #{==:#{FOO},baz}
# found #{}: ==:#{FOO},baz
# modifier 0 is ==
#  expanding format: #{FOO}
#  found #{}: FOO
#  format 'FOO' found: bar
#  replaced 'FOO' with 'bar'
#  result is: bar
#  expanding format: baz
#  result is: baz
# compare == left is: bar
# compare == right is: baz
# replaced '==:#{FOO},baz' with '0'
# result is: 0
0