Getting the return value from an internal Vim command in Vimscript

Question

I want to do something like

let colors = execute(":highlight")

This is obviously incorrect; all I can do is execute(":highlight") which will open a window, but what I really need is to get the contents of that window into a variable — much like a system() call would do for external commands. Can this be done?

Answer 1

There is a command called :redir that is specifically designed to capture the output of one or more commands into a file, a register, or a variable. The latter option is what we want in this case:

:redir => colors
:silent highlight
:redir END

To see the complete list of the ways to invoke the command, refer to :help :redir. See also my answer to the question “Extending a highlighting group in Vim” for another practical use of :redir.

Answer 2

let colors = lh#askvim#exe(':hi')

Which just encapsulates :redir. Or even better:

let colors = lh#askvim#execute(':hi')

which returns the result as a list variable, either through :redir if we have no choice, or through execute() when it's defined. This new approach is to be prefered as it has less undesired side effects.