A simple Vimscript function `GitCurrentBranch()` which returns the git branch of the current buffer. It is really nothing fancy - it just loads the branch into the buffer variable `b:gitbranch` upon reading a buffer via `autocmd`. Ideally, it can be used in the statusline with `:set statusline+=%{b:gitbranch}`

git-current-branch.vim

" Retrieves git branch of the current file
" Perfect for feeding the branch into the statusline
" Depends on autocmd
"
" USAGE:--------------------------------------------
"
" Call in statusline as %{b:gitbranch}
" :set statusline+={%b:gitbranch}

function! GitCurrentBranch()
    " Stores current working directory
    let lastdir = getcwd()
    " Changes temporarily to the directory containing the buffer
    let bufdir = expand('%:p:h')
    if bufdir != lastdir
      lcd `=bufdir`
    endif
    " Retrieves git branch after changing directory
    let branch = system("git branch --no-color 2> /dev/null | cut -d' ' -f2")
    " Then changes back
    if bufdir != lastdir
      lcd `=lastdir`
    endif

    if branch != ''
        return '[GIT-BRANCH=' . substitute(branch, '\n', '', 'g') . ']' 
    en  
    return ''
endfunction

autocmd BufRead,BufNewFile * let b:gitbranch=GitCurrentBranch()



" Inspired By http://amix.dk/blog/post/19571