Eu usei ** para indicar que é importante.
de man wget
-O file
--output-document=file
The documents will not be written to the appropriate files, but all
will be concatenated together and written to file. ** If - is used as
file, documents will be printed to standard output, disabling link
conversion. (Use ./- to print to a file literally named -.) **
Use of -O is not intended to mean simply "use the name file instead
of the one in the URL;" rather, it is analogous to shell
redirection: wget -O file http://foo is intended to work like wget
-O - http://foo > file; file will be truncated immediately, and all
downloaded content will be written there.
e de man apt-key
add filename
Add a new key to the list of trusted keys. The key is read from
filename, or ** standard input if filename is -.**
isso explica o seu comando.