When starting a bash shell process, what are the default environment variables, except those specified in the startup file?Is it correct that some bash or sh builtin variables (listed in https://www.gnu.org/software/bash/manual/html_node/Bourne-Shell-Variables.html#Bourne-Shell-Variables and https://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html) are default environment variables while other bash or sh builtin variables are not? What kinds of bash or sh builtin variables are default environment variables?In http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html  it seems that all or most of the builtin variables in bash are environment variables by default, but I am not sure.
What are the environment variables by default?
bash;environment variables