.vimrc

" git commit message config
autocmd FileType gitcommit set textwidth=72
autocmd FileType gitcommit set colorcolumn=73

" git populate commit template with variables
" https://vi.stackexchange.com/a/11900
function! s:expand_commit_template() abort
  let branch = split(matchstr(system('git rev-parse --abbrev-ref HEAD'), '\p\+'), "-")

  let context = {
        \ 'TICKET_SYSTEM': branch[0],
        \ 'TICKET_NUMBER': branch[1],
        \ }

  let lnum = nextnonblank(1)
  while lnum && lnum < line('$')
    call setline(lnum, substitute(getline(lnum), '\${\(\w\+\)}',
          \ '\=get(context, submatch(1), submatch(0))', 'g'))
    let lnum = nextnonblank(lnum + 1)
  endwhile
endfunction

autocmd BufRead */.git/COMMIT_EDITMSG call s:expand_commit_template()