How can I run a script with sudo? I get ".: command not found"
You need to run
sudo ./scriptfile
You tried
sudo . /scriptfile
which is different due to the space after the dot. . or it's equivalent source is a shell builtin, not a command. That's why the command you tried produces the error sudo: .: command not found.
Note:
./scriptfile
will execute the file with the name scriptfile in the current directory. The file needs to be executable.
. /scriptfile
will source the file /scriptfile (remind that this is an absolute path here). The file doesn't need to be executable to do this, it only needs to be readable.