Given a multi-line string and a sequence of Vim navigation commands

get_char_after_vim_commands.rb

# h for left, j for down, k for up, and l for right)

def get_char_after_vim_commands(string, commands)
  lines = string.lines.map(&:chomp)
  row, col = 0, 0

  commands.each_char do |cmd|
    dr, dc = {"h" => [0, -1], "j" => [1, 0], "k" => [-1, 0], "l" => [0, 1]}[cmd] || [0, 0]
    row = (row + dr).clamp(0, lines.size - 1)
    col = (col + dc).clamp(0, [lines[row].size - 1, 0].max)
  end

  lines[row][col]
end