I am trying to use vim's :exe command to vimgrep the word under cursor, but I am having problems with the command construction:
If my command is
:execute "vimgrep " shellescape(expand("<cword>")) " somedir"
it expands to
execute "vimgrep 'foo' somedir"
But if my command is
execute "vimgrep " .. shellescape(expand("<cword>")) .. " somedir"
it expands to
execute "vimgrep '' somedir"
How do I correctly expand <cword> raw, without single quotes?
Wrapping something in single quotes is the main purpose of shellescape(). If you don't want those quotes, don't use shellescape().
:help shellescape() is used for preparing commands before they are shelled out. Since :help vimgrep is an internal tool and nothing is sent to a shell, there is no need for quoting.
This means that the following command should cover most of your needs:
:execute "vimgrep " .. expand("<cword>") .. " somedir"
Also, :vimgrep searches in files, not directories. Your command should then look more like:
:execute "vimgrep " .. expand("<cword>") .. " somedir/*"