If you want to check something in bash, use
In your case you want to know what is .
$ type .
. is a shell builtin
shell builtin means that . is inside
bash shell. You can find information about shell builtins in
bash manual page. There is a big section SHELL BUILTIN COMMANDS
$ man bash
SHELL BUILTIN COMMANDS
Unless otherwise noted, each builtin command documented in this section
as accepting options preceded by - accepts -- to signify the end of the
options. The :, true, false, and test builtins do not accept options
and do not treat -- specially. The exit, logout, break, continue, let,
and shift builtins accept and process arguments beginning with - with‐
out requiring --. Other builtins that accept arguments but are not
specified as accepting options interpret arguments beginning with - as
invalid options and require -- to prevent this interpretation.
No effect; the command does nothing beyond expanding arguments
and performing any specified redirections. A zero exit code is
. filename [arguments]
source filename [arguments]
Read and execute commands from filename in the current shell
environment and return the exit status of the last command exe‐
cuted from filename. If filename does not contain a slash,
filenames in PATH are used to find the directory containing
filename. The file searched for in PATH need not be executable.
When bash is not in posix mode, the current directory is
searched if no file is found in PATH. If the sourcepath option
to the shopt builtin command is turned off, the PATH is not
searched. If any arguments are supplied, they become the posi‐
tional parameters when filename is executed. Otherwise the
positional parameters are unchanged. The return status is the
status of the last command exited within the script (0 if no
commands are executed), and false if filename is not found or
cannot be read.