Set runtimepath, adding a directory from an expression in vim?

Question

Inn ~/script.vim, I have:

set runtimepath+=string(substitute(expand("%:p"), 'script\.vim', '', 'g'))

I have an alias in .bashrc:

alias vimscript="vim -S ~/script.vim"

Running string(substitute(expand("%:p"), 'script\.vim', '', 'g')) works as intended.

The problem is when using it in the set runtimepath expression, it doesn't work when I call vimscript in terminal which calls script.vim. When I run set rtp in vim after being called by vimscript to check the runtimepath, the desired appended string isn't showed (but the other ones are there).

Answer 1

I have some additions to @Laurence Gonsalves answer:

1. There is also «concat and assign» operator: .=, so

   let foo=foo.bar
   

   can be rewritten as

   let foo.=bar
   

2. Code

   let &runtimepath.=','.string(path)
   

   will append ,'/some/path' to &runtimepath, while you probably need ,/some/path.

3. I guess that you want to append path to your script to runtimepath. If it is true, then your code should be written as

   let &runtimepath.=','.escape(expand('<sfile>:p:h'), '\,')
   

   inside a script, or

   let &runtimepath.=','.escape(expand('%:p:h'), '\,')
   

   from current editing session (assuming that you are editing your script in the current buffer).

Answer 2

The right hand site of a set command is not an expression, it's a literal string.

You can manipulate options (the things set sets) by using let and prefixing the option name with an &. eg:

let &runtimepath=substitute(expand("%:p"), 'script\.vim', '', 'g')

To append to runtimepath with a let you can do something like:

let &runtimepath=&runtimepath . ',' . substitute(expand("%:p"), 'script\.vim', '', 'g')

(The . is the string concatenation operator.)