gistfile1.txt

require 'ffi'

module ChdirExec
  extend FFI::Library
  ffi_lib 'c'

  attach_function :execlp, [:string, :varargs], :int
  attach_function :chdir, [:string], :int

  def self.chdir_exec(dir, cmd, *argv)
    chdir(dir)
    argv.unshift(cmd)
    argv = ([:string] * argv.size).zip(argv).flatten
    argv <<:int
    argv << 0
    execlp(cmd, *argv)
    raise SystemCallError.new(FFI.errno)
  end
end

ChdirExec.chdir_exec('/bin', '/bin/sh')