Tmux reloads Bash .profile - bash

Question

Suppose I have this in my .profile
export VALUE=x:$VALUE
Then when I start a terminal and do
$ printenv VALUE
x:
the result is what is expected, i.e., VALUE is equal do x:.
Also if I keep launching bash like this
$ printenv VALUE
x:
$ bash
bash-3.2$ printenv VALUE
x:
bash-3.2$
the result is what is expected too.
However, if I start a terminal and launch tmux instead, I get
$ printenv VALUE
x:
$ tmux
$ printenv VALUE
x:x:
and the final VALUE is not equal do x:.
How can I launch tmux so that this does not happen, and it behaves like a fresh bash session?
I am on macOS 10.12.6 (Sierra)
Thanks

Answer 1

There are several reasons why your ~/.profile happens to be sourced more than once.
One would be that tmux is started in a way so that it behaves like a login shell. As such, it will source the ~/.profile naturally (see man bash at INVOCATION). You can start tmux as a login shell by providing the option -l. You didn't mention giving this explicitly, so I guess you didn't, but maybe it was implicitly passed to tmux by some alias or similar. You might want to double check on this (enter type tmux for instance).
The more probable reason is that tmux just starts a shell which then assumes that it is a login shell and thus sources ~/.profile. This in a way is also correct, because starting a terminal muxer can be seen as the process of logging in. More on this can be found here: https://superuser.com/a/970847/153009
The third possibility (which was the reason in my case when I tried to reproduce your case) is that your ~/.bashrc sources your ~/.profile intentionally and explicitly. Although this is against the original design, one finds this very often. Obviously it often solves ugly issues with missing executions of invocation scripts.
You can check for this by giving out ${BASH_SOURCE[*]} in the beginning of the ~/.profile (redirect it to a file to be sure you can see it later).
Because of problems with this, I have the following script snippet in each of my invocation scripts (.bashrc, .profile, etc.):
(
echo "$(date): .profile: $0: $$"; pstree -lp $PPID 2>/dev/null
echo "BASH_SOURCE: ${BASH_SOURCE[*]}"
echo "FUNCNAME: ${FUNCNAME[*]}"
echo "BASH_LINENO: ${BASH_LINENO[*]}"
) >> ~/var/log/config-scripts.log
(Adjust the name .profile in the first line according to the script name of course.)

Answer 2

It seems there is no way to avoid tmux from starting its own shell without inheriting the environment variables of the shell where tmux is called. This means that startup shell scripts must take care if they are running inside tmux. For example, in bash, this can be done
if [ -n "$TMUX" ];
then
echo Inside tmux
else
echo Outside tmux
fi