:w !sudo tee %…
% means “the current file”
As eugene y pointed out,
% does indeed mean “the current file name”, which is passed to
tee so that it knows which file to overwrite.
(In substitution commands, it’s slightly different; as
:help :% shows, it’s
equal to 1,$ (the entire file) (thanks to @Orafu for pointing out that this does not evaluate to the filename). For example,
:%s/foo/bar means “in the current file, replace occurrences of
bar.” If you highlight some text before typing
:s, you’ll see that the highlighted lines take the place of
% as your substitution range.)
:w isn’t updating your file
One confusing part of this trick is that you might think
:w is modifying your file, but it isn’t. If you opened and modified
file1.txt, then ran
:w file2.txt, it would be a “save as”;
file1.txt wouldn’t be modified, but the current buffer contents would be sent to
file2.txt, you can substitute a shell command to receive the buffer contents. For instance,
:w !cat will just display the contents.
If Vim wasn’t run with sudo access, its
:w can’t modify a protected file, but if it passes the buffer contents to the shell, a command in the shell can be run with sudo. In this case, we use
tee, picture the
tee command as a T-shaped pipe in a normal bash piping situation: it directs output to specified file(s) and also sends it to standard output, which can be captured by the next piped command.
For example, in
ps -ax | tee processes.txt | grep 'foo', the list of processes will be written to a text file and passed along to
+-----------+ tee +------------+ | | -------- | | | ps -ax | -------- | grep 'foo' | | | || | | +-----------+ || +------------+ || +---------------+ | | | processes.txt | | | +---------------+
(Diagram created with Asciiflow.)
tee man page for more info.
Tee as a hack
In the situation your question describes, using
tee is a hack because we’re ignoring half of what it does.
sudo tee writes to our file and also sends the buffer contents to standard output, but we ignore standard output. We don’t need to pass anything to another piped command in this case; we’re just using
tee as an alternate way of writing a file and so that we can call it with
Making this trick easy
You can add this to your
.vimrc to make this trick easy-to-use: just type
" Allow saving of files as sudo when I forgot to start vim using sudo. cmap w!! w !sudo tee > /dev/null %
> /dev/null part explicitly throws away the standard output, since, as I said, we don’t need to pass anything to another piped command.