the scope of variable in vim

Question

I believe the following script in vimrc, which try to set spellfile, has something to do with the scope of vim variable. Especially the difference of $var and g:var:

I can't figure out what's wrong with this:

let g:spelldir ='~/.vim/myvim/spell'
if !exists( 'g:spelldir' )
  silent exec '!mkdir -p ' . g:spelldir
endif
au FileType tex setlocal spf= g:spelldir/en.utf-8.add

while it works if we change g:spelldir to $spelldir.

Answer 1

1. Use isdirectory not exists to check if a directory exists.

2. set/setlocal does not expand variables but it does (sometimes) expand environment variables, which explains what you're seeing. Use this instead:

   au FileType tex exe 'setlocal spf='.g:spelldir.'/en.utf-8'
   

The g:spelldir is copied into the setlocal string when the FileType autocommand is triggered, then the whole string is executed. It has nothing to do with variable scope, g: is global.