How can you automatically remove trailing whitespace in vim

Question

I am getting \'trailing whitespace\' errors trying to commit some files in git.

I want to remove these trailing whitespace characters automatically right before I sa

Answer 1

Copied and pasted from http://blog.kamil.dworakowski.name/2009/09/unobtrusive-highlighting-of-trailing.html (the link no longer works, but the bit you need is below)

"This has the advantage of not highlighting each space you type at the end of the line, only when you open a file or leave insert mode. Very neat."

highlight ExtraWhitespace ctermbg=red guibg=red
au ColorScheme * highlight ExtraWhitespace guibg=red
au BufEnter * match ExtraWhitespace /\s\+$/
au InsertEnter * match ExtraWhitespace /\s\+\%#\@