How does the vim "write with sudo" trick work?

Question

Many of you have probably seen the command that allows you to write on a file that needs root permission, even when you forgot to open vim with sudo:

:w !sudo tee %

The thing is that I don't get what is exactly happening here.

I have already figured this: w is for this

                                                        *:w_c* *:write_c*
:[range]w[rite] [++opt] !{cmd}
                        Execute {cmd} with [range] lines as standard input
                        (note the space in front of the '!').  {cmd} is
                        executed like with ":!{cmd}", any '!' is replaced with
                        the previous command |:!|.

so it passes all the lines as standard input.

The !sudo tee part calls tee with administrator privileges.

For all to make sense, the % should output the filename (as a parameter for tee), but I can't find references on the help for this behavior.

tl;dr Could someone help me dissect this command?

Answer 1

:help cmdline-special