Vim function : how to expand vim variable in shell command?

Question

I'm trying to write a vim function to update ctags and cscope databases. I'm trying to save the vim variable projectRoot in environment variable then expand this enviroment variable in the find command. But it is not working. Here is my try:

let projectRoot="/mnt/hgfs/projects/myProject/"

function! UpdateTagDB()
   :cd /
   :execute("let ProRoot=".g:projectRoot)
   :find $ProRoot -name '*.c' -o -name '*.h' > $ProRoot/cscope.files<cr>
   :execute("cd ".g:projectRoot)
   :!ctags -R .<cr>
   :!cscope -bR<cr>
endfunction

nnoremap <F5> :call UpdateTagDB()

When hitting F5, it gives me:

line 2:
E15: Invalid expression: /mnt/hgfs/projects/myProject/
line 3:
E345: Can't find file "$ProRoot -name '*.c' -o -name '*.h' > $ProRoot/cscope.files<cr>" in path

What is missing and how to get it to work?

Answer 1

The :execute command will assemble an Ex command from strings and evaluate it.

Here, in this case, it's actually breaking your command, since it's expanding the g:projectRoot string and forming a string that is an invalid Ex command, since the quotes around the path are now missing. That command is actually equivalent to:

let ProRoot=/mnt/hgfs/projects/myProject/

Just drop the :execute should be enough to fix it.

Also, to set an environment variable, you need to use the $ prefix on the let command as well.

let $ProRoot = g:projectRoot

Finally, you don't need : anywhere inside a Vimscript function, it's all executed as Ex commands anyways. (The : doesn't break it, but it looks much nicer without it.)

Finally, your find is a shell command, so you need a ! to have it executed by the shell.

There are a few more issues in the following lines, namely you shouldn't have <CR> at the end of commands, and you shouldn't have parents on the :execute for cd (parents denotes a function call, but this should be a command.)

Putting it all together:

function! UpdateTagDB()
    cd /
    let $ProRoot = g:projectRoot
    !find $ProRoot -name '*.c' -o -name '*.h' > $ProRoot/cscope.files
    execute "cd ".g:projectRoot
    !ctags -R .
    !cscope -bR
endfunction

Finally, you do need a <CR> in your :map command. You probably also want to make it <silent> so it doesn't print the :call command on the command-line when executed:

nnoremap <silent> <F5> :call UpdateTagDB()<CR>