add docstring examples

base/util.jl

@@ -285,6 +285,27 @@ is encountered or EOF (^D) character is entered on a blank line. If a `default`
 then the user can enter just a newline character to select the `default`. A `timeout` in seconds
 greater than 0 can be provided, after which the default will be returned.
 
+For instance, the user enters a value and hits `return`:
+```julia
+julia> Base.prompt("Proceed? y/n"; default="n", timeout=5)
+Proceed? y/n [n] timeout 5 seconds: y
+"y"
+```
+
+The user hits `return` alone to select the default:
+```julia
+julia> Base.prompt("Proceed? y/n"; default="n", timeout=5)
+Proceed? y/n [n] timeout 5 seconds:
+"n"
+```
+
+The user doesn't input and hit `return` before the timeout, so default returns:
+```julia
+julia> Base.prompt("Proceed? y/n"; default="n", timeout=5)
+Proceed? y/n [n] timeout 5 seconds: timed out
+"n"
+```
+
 See also `Base.getpass` and `Base.winprompt` for secure entry of passwords.
 """
 function prompt(input::IO, output::IO, message::AbstractString; default::AbstractString="", timeout::Union{Nothing, Real} = nothing)
@@ -303,7 +324,6 @@ function prompt(input::IO, output::IO, message::AbstractString; default::Abstrac
         end
     else
         msg = !isempty(default) ? "$message [$default]: " : "$message: "
-        timeout_timer = nothing
     end
     print(output, msg)
     uinput = readline(input, keep=true)