How to Change the Prompt in Elixir IEx with Examples


Percy Grunwald's Profile Picture

Written by Percy Grunwald

— Last Updated February 22, 2019

The default prompt in Elixir’s IEx is pretty simple:

iex(1)> IO.puts("Hello, World!")
Hello, World!
:ok
iex(2)>

Since I write a lot of tutorials that require me to paste IEx output, I’d prefer that the parentheses and counter weren’t there. I just want a simple iex> on every line, like this:

iex> IO.puts("Hello, World!")
Hello, World!
:ok
iex>

How to change the prompt in IEx

You can configure the prompt by using the IEx.configure/1 function and modifying the :default_prompt and :alive_prompt options. Let’s take a look at the default configuration with IEx.configuration/0:

iex(2)> IEx.configuration()
[
  default_prompt: "%prefix(%counter)>",
  colors: [],
  alive_prompt: "%prefix(%node)%counter>",
  inspect: [pretty: true],
  history_size: 20
]

Let’s change the prompts to be just "%prefix>":

iex(3)> IEx.configure(default_prompt: "%prefix>", alive_prompt: "%prefix>")     
:ok
iex>

The prompt has immediately changed to iex>, great!

How to persist IEx configuration changes to new sessions

If I restart IEx after applying the changes above, the prompt is right back to its default:

$ iex
Erlang/OTP 21 [erts-10.1.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe]

Interactive Elixir (1.7.4) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)>

To persist the changes, I need to add this configuration line to the local ./.iex.exs or the global ~/.iex.exs:

# ~/.iex.exs

IEx.configure(default_prompt: "%prefix>", alive_prompt: "%prefix>")

The ~/.iex.exs function is run every time IEx starts. If I restart IEx now, my configuration is applied at startup:

$ iex
Erlang/OTP 21 [erts-10.1.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe]

Interactive Elixir (1.7.4) - press Ctrl+C to exit (type h() ENTER for help)
iex>

Nice! 👍

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