How to enable map command in vim?

Question

How to enable map command only when filetype is 'perl'?

something like:

if(&ft=='perl')
  map ,pt <ESC>:%! perltidy<CR>
endif

but it doesn't work.

Answer 1

I found the shorter way.

Add this line to your ~/.vimrc

au FileType perl nnoremap <buffer> _t <ESC>:%! perltidy<CR>