>>107800139
Here's some commands so you can answer yourself some of these questions.
$ which sh
/usr/bin/sh
$ file $(which sh)
/usr/bin/sh: symbolic link to bash
$ type .
. is a shell builtin
$ help . # also known as "source"
.: . filename [arguments]
Execute commands from a file in the current shell.
(...omitted...)
$ echo $SHELL
/bin/bash
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