vim: how to get filetype in plugin script

Question

How do I get the current filetype in a vimscript, say in .vimrc or a regular plugin script? The line

echo &filetype

returns an empty string.

Answer 1

In a function:

let current_filetype = &filetype

On the command line:

:echo &filetype

&filetype is empty when there's no filetype (obviously). If you try to use it when there's no buffer loaded you'll just get nothing.

edit

&filetype is only useful when you need to know the current filetype in a function executed at runtime when you are editing a buffer.

&filetype is only set when a buffer has been determined to be of some filetype. When it is executed, a script (vimrc, ftplugin, whatever) doesn't go through what it would go when it is edited: no filetype checking, no &filetype.

An example would be a function that displays the current file in a different external app depending on its filetype. Using &filetype in any other context doesn't make sense because it will be empty.

Answer 2

You need to consider the timing of your plugin. When your plugin script is sourced during the startup of Vim, no buffer has yet been loaded, so &filetype is empty. Therefore, something like this

let s:formatprgvarname = "g:formatprg_".&filetype

does not work! (For a filetype plugin (in ~/.vim/ftplugin/), this is different; those are sourced only when the filetype has been detected. But as I understand you want a general-purpose plugin that considers the current filetype.)

Instead, do away with the script-local variable s:formatprgvarname and resolve &filetype at the point of action; i.e. when your autoformat functionality is triggered (by mapping or custom command). If you have no such trigger, you can hook into the FileType event and set a (preferably buffer-local) variable then:

autocmd FileType * let b:formatprgvarname = "g:formatprg_".&filetype