How to correctly use a local script variable

Question

Suppose I have the following code:

let s:user_config=fnamemodify('user.vim', ':p')
echom 'file found: ' . s:user_config
if filereadable(s:user_config)  
  source s:user_config
else
  echom s:user_config . 'was not found'
endif

If I run this, I get:

file found: /home/ninrod/vim_test/user.vim
Error detected while processing /home/ninrod/vim_test/test.vim:
line    4:
E484: Can't open file s:user_config
Press ENTER or type command to continue

on the echo line, the variable s:user_config was correctly interpolated. How do I tell vim to interpolate the s:user_config on the source line?

Answer 1

As it is written, your code will execute literally source s:user_config and you want to execute source [content of the variable].

You can use execute() like this:

execute "source " . s:user_config

:h :execute:

:exe[cute] {expr1} ..   Executes the string that results from the evaluation
            of {expr1} as an Ex command.
            Multiple arguments are concatenated, with a space in
            between.  To avoid the extra space use the "."

Answer 2

I'm not sure you're aware of it, but most of the time we don't need to do what you're trying to achieve the way you're doing it.

If you respect vim standard way of organizing scripts, if you drop your file into ~/.vim/plugin/ it'll be automatically loaded. You cannot know when (regarding the load order of all the scripts in the same directory -- it seems to be sorted lexicographically nowadays), but it'll be loaded. This also means: drop your configuration files in ~/.vim not in ~/vim_test.

If you need a mapping/command/abbreviation defined in that plugin, you can enforce its load with :runtime plugin/user.vim. Don't forget to add inclusion guards to avoid the script to be loaded twice.

If you need a function from the plugin, then make it an autoload plugin, drop it in: ~/.vim/autoload. Prefix the function name with the plugin name, like user#my_function(), and simply call that function from where you need it: call user#my_function(parameters).

I haven't described the situation with filetype specific configuration, but it isn't much different.