How do I programmatically inject keystrokes into Vim's input queue from a function or mapping?

Explanation

The feedkeys({keys}, {flags}) function inserts a string of keystrokes into Vim's input queue as if the user had typed them. This is invaluable when you need to trigger complex sequences from a function or mapping — especially when you need to switch modes, pass special keys, or pre-populate a search or command prompt for the user to continue editing.

How it works

call feedkeys("iHello World\<Esc>", 'n')

• First argument: the key sequence string. Use \<Key> notation for special keys: \<Esc>, \<CR>, \<C-w>, etc.
• Second argument flags control how keys are processed:
  • 'n' — apply no remapping (like noremap), the most common choice
  • 't' — process keys as if typed by the user (goes through the typeahead buffer)
  • 'x' — execute the keys immediately and only return after processing completes
  • 'i' — insert at the head of the typeahead buffer (runs before any already-pending input)

Example

A mapping that opens a search prompt pre-filled with the word under the cursor and lets the user edit it before executing:

nnoremap <leader>/ :call feedkeys('/\<' . expand('<cword>') . '\>', 'n')<CR>

A function that simulates pressing <C-d> to list completion candidates after triggering omnicomplete:

function! ShowOmniList()
  call feedkeys("\<C-x>\<C-o>\<C-d>", 'n')
endfunction

Tips

• Use feedkeys() when :normal! is not enough — for example, when you need to pass keystrokes that change modes or interact with the command line
• The 'x' flag forces synchronous execution and is useful in tests and scripts where you need the result immediately
• Avoid feedkeys() for simple normal-mode operations; :normal! {keys} is simpler and sufficient in those cases
• In Neovim, vim.api.nvim_feedkeys() provides the Lua equivalent with the same semantics