How to check if an external command exists in Lua

Question

How do I translate this VimL code into Lua?

if executable('rg')
  set grepprg=rg\ --vimgrep
endif

Answer 1

The answer below assumes you are running neovim and not vim.

:h vim.cmd() lets you execute a vimscript command from lua. It takes the command as a string. So you can wrap any vimscript in a string and pass it to :lua vim.cmd() and it should work.

vim.cmd[[
if executable('rg')
  set grepprg=rg\ --vimgrep
endif
]]

On the other hand, if you want a more lua-like approach, you can use :h vim.fn to call any vim function, both user-defined and built-in. With :h vim.o or :h vim.opt you can set the vim options.

if vim.fn.executable('rg') == 1 then
  vim.o.grepprg = 'rg --vimgrep'
end