The Trick

You open a file, edit it and save it only to get the E45 error message that says:

E45: 'readonly' option is set (add ! to override)

You now realise that only root can edit the file. What do you? Start over? No, instead try this:

:w !sudo tee "%"

I learnt this trick recently from the comment section of Tip #975 on the Vim Tips website.

Explanation

How does the :w !sudo tee "%" trick work? Let us look at the command part-by-part:

• :w !{cmd}

  Execute {cmd} with all lines in buffer as standard input.

• "%"

  The % is replaced with the current filename. The quotes around it keeps the filename as a single argument even if it contains whitespace.

• tee {file}

  The tee command is a Unix command (not a Vim command). It copies standard input to standard output and {file}.

More Information

For more information on this command, enter the following commands in Vim:

:help :w_c
:help current-file
:help :_%

Also, enter the following command in shell:

man tee

I hope this was fun!