IEx — IEx v1.16.3

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# View Source IEx (IEx v1.16.3)

Elixir's interactive shell.

Some of the functionalities described here will not be available depending on your terminal. In particular, if you get a message saying that the smart terminal could not be run, some of the features described here won't work.

## Helpers

IEx provides a bunch of helpers. They can be accessed by typing `h()` into the shell or as a documentation for the `IEx.Helpers` module.

## Autocomplete

To discover a module's public functions or other modules, type the module name followed by a dot, then press tab to trigger autocomplete. For example:

    Enum.

A module may export functions that are not meant to be used directly: these functions won't be autocompleted by IEx. IEx will not autocomplete functions annotated with `@doc false`, `@impl true`, or functions that aren't explicitly documented and where the function name is in the form of `__foo__`.

Autocomplete is available by default on Windows shells from Erlang/OTP 26. In earlier versions, you may need to pass the `--werl` option when starting IEx, such as `iex --werl` (or `iex.bat --werl` if using PowerShell). `--werl` may be permanently enabled by setting the `IEX_WITH_WERL` environment variable to `1`.

## Encoding and coloring

IEx expects inputs and outputs to be in UTF-8 encoding. This is the default for most Unix terminals but it may not be the case on Windows. If you are running on Windows and you see incorrect values printed, you may need to change the encoding of your current session by running `chcp 65001` before calling `iex` (or before calling `iex.bat` if using PowerShell).

Similarly, ANSI coloring is enabled by default on most Unix terminals. They are also available on Windows consoles from Windows 10 and on Erlang/OTP 26 or later. For earlier Erlang/OTP versions, you can explicitly enable it for the current user in the registry by running the following command:

    $ reg add HKCU\Console /v VirtualTerminalLevel /t REG_DWORD /d 1

After running the command above, you must restart your current console.

## Shell history

It is possible to get shell history by passing some options that enable it in the VM. This can be done on a per-need basis when starting IEx:

    $ iex --erl "-kernel shell_history enabled"

If you would rather enable it on your system as a whole, you can use the `ERL_AFLAGS` environment variable and make sure that it is set accordingly on your terminal/shell configuration.

On Unix-like / Bash:

    $ export ERL_AFLAGS="-kernel shell_history enabled"

On Windows:

    $ set ERL_AFLAGS "-kernel shell_history enabled"

On Windows 10 / PowerShell:

    $ $env:ERL_AFLAGS = "-kernel shell_history enabled"

## Expressions in IEx

As an interactive shell, IEx evaluates expressions. This has some interesting consequences that are worth discussing.

The first one is that the code is truly evaluated and not compiled. This means that any benchmarking done in the shell is going to have skewed results. So never run any profiling nor benchmarks in the shell.

Second, IEx allows you to break an expression into many lines, since this is common in Elixir. For example:

    iex(1)> "ab
    ...(1)> c"
    "ab\nc"

In the example above, the shell will be expecting more input until it finds the closing quote. Sometimes it is not obvious which character the shell is expecting, and the user may find themselves trapped in the state of incomplete expression with no ability to terminate it other than by exiting the shell.

For such cases, there is a special break-trigger (`#iex:break`) that when encountered on a line by itself will force the shell to break out of any pending expression and return to its normal state:

    iex(1)> ["ab
    ...(1)> c"
    ...(1)> "
    ...(1)> ]
    ...(1)> #iex:break
    ** (TokenMissingError) iex:1: incomplete expression

## Pasting multiline expressions into IEx

IEx evaluates its input line by line in an eager fashion. If at the end of a line the code seen so far is a complete expression, IEx will evaluate it at that point.

    iex(1)> [1, [2], 3]
    [1, [2], 3]

To prevent this behaviour breaking valid code where the subsequent line begins with a binary operator, such as `|>/2` or `++/2` , IEx automatically treats such lines as if they were prepended with `IEx.Helpers.v/0`, which returns the value of the previous expression, if available.

    iex(1)> [1, [2], 3]
    [1, [2], 3]
    iex(2)> |> List.flatten()
    [1, 2, 3]

The above is equivalent to:

    iex(1)> [1, [2], 3]
    [1, [2], 3]
    iex(2)> v() |> List.flatten()
    [1, 2, 3]

If there are no previous expressions in the history, the pipe operator will fail:

    iex(1)> |> List.flatten()
    ** (RuntimeError) v(-1) is out of bounds

If the previous expression was a match operation, the pipe operator will also fail, to prevent an unsolicited break of the match:

    iex(1)> x = 42
    iex(2)> |> IO.puts()
    ** (SyntaxError) iex:2:1: pipe shorthand is not allowed immediately after a match expression in IEx. To make it work, surround the whole pipeline with parentheses ('|>')
        |
      2 | |> IO.puts()
        | ^

Note, however, the above does not work for `+/2` and `-/2`, as they are ambiguous with the unary `+/1` and `-/1`:

    iex(1)> 1
    1
    iex(2)> + 2
    2

## The BREAK menu

Inside IEx, hitting `Ctrl+C` will open up the `BREAK` menu. In this menu you can quit the shell, see process and ETS tables information and much more.

## Exiting the shell

There are a few ways to quit the IEx shell:

- via the `BREAK` menu (available via `Ctrl+C`) by typing `q`, pressing enter
- by hitting `Ctrl+C`, `Ctrl+C`
- by hitting `Ctrl+\`

If you are connected to remote shell, it remains alive after disconnection.

## `dbg` and breakpoints

IEx integrates with `Kernel.dbg/2` and introduces a backend that can pause code execution. To enable it, you must pass `--dbg pry`:

    $ iex --dbg pry

For example, take the following function:

    def my_fun(arg1, arg2) do
      dbg(arg1 + arg2)
      ... implementation ...
    end

When the code is executed with `iex` (most often by calling `iex --dbg pry -S mix`), it will ask you permission to use "pry". If you agree, it will start an IEx shell in the context of the function above, with access to its variables, imports, and aliases. However, you can only access existing values, it is not possible to access private functions nor change the execution itself (hence the name "pry").

When using `|> dbg()` at the end of a pipeline, you can pry each step of the pipeline. You can type `n` whenever you want to jump into the next pipe. Type `continue` when you want to execute all of the steps but stay within the pried process. Type `respawn` when you want to leave the pried process and start a new shell.

Alternatively, you can start a pry session directly, without `dbg/2` by calling `IEx.pry/0`.

IEx also allows you to set breakpoints to start pry sessions on a given module, function, and arity you have no control of via `IEx.break!/4`. Similar to pipelines in `dbg()`, `IEx.break!/4` allows you to debug a function line by line and access its variables. However, breakpoints do not contain information about imports and aliases from the source code.

When using `dbg` or breakpoints with tests, remember to pass the `--trace` to `mix test` to avoid running into timeouts:

    $ iex -S mix test --trace
    $ iex -S mix test path/to/file:line --trace

## The User switch command

Besides the `BREAK` menu, one can type `Ctrl+G` to get to the `User switch command` menu. When reached, you can type `h` to get more information.

In this menu, developers are able to start new shells and alternate between them. Let's give it a try:

    User switch command
     --> s 'Elixir.IEx'
     --> c

The command above will start a new shell and connect to it. Create a new variable called `hello` and assign some value to it:

    hello = :world

Now, let's roll back to the first shell:

    User switch command
     --> c 1

Now, try to access the `hello` variable again:

    hello
    ** (CompileError) undefined variable "hello"

The command above fails because we have switched shells. Since shells are isolated from each other, you can't access the variables defined in one shell from the other one.

The `User switch command` can also be used to terminate an existing session, for example when the evaluator gets stuck in an infinite loop or when you are stuck typing an expression:

    User switch command
     --> i
     --> c

The `User switch command` menu also allows developers to connect to remote shells using the `r` command. A topic which we will discuss next.

## Remote shells

IEx allows you to connect to another node in two fashions. First of all, we can only connect to a shell if we give names both to the current shell and the shell we want to connect to.

Let's give it a try. First, start a new shell:

    $ iex --sname foo
    iex(foo@HOST)1>

The string between the parentheses in the prompt is the name of your node. We can retrieve it by calling the `node/0` function:

    iex(foo@HOST)1> node()
    :"foo@HOST"
    iex(foo@HOST)2> Node.alive?()
    true

For fun, let's define a simple module in this shell too:

    iex(foo@HOST)3> defmodule Hello do
    ...(foo@HOST)3>   def world, do: "it works!"
    ...(foo@HOST)3> end

Now, let's start another shell, giving it a name as well:

    $ iex --sname bar
    iex(bar@HOST)1>

If we try to dispatch to `Hello.world/0`, it won't be available as it was defined only in the other shell:

    iex(bar@HOST)1> Hello.world()
    ** (UndefinedFunctionError) undefined function Hello.world/0

However, we can connect to the other shell remotely. Open up the `User switch command` prompt (Ctrl+G) and type:

    User switch command
     --> r 'foo@HOST' 'Elixir.IEx'
     --> c

Now we are connected into the remote node, as the prompt shows us, and we can access the information and modules defined over there:

    iex(foo@HOST)1> Hello.world()
    "it works!"

In fact, connecting to remote shells is so common that we provide a shortcut via the command line as well:

    $ iex --sname baz --remsh foo@HOST

Where "remsh" means "remote shell". In general, Elixir supports:

- remsh from an Elixir node to an Elixir node
- remsh from a plain Erlang node to an Elixir node (through the ^G menu)
- remsh from an Elixir node to a plain Erlang node (and get an `erl` shell there)

Connecting an Elixir shell to a remote node without Elixir is not supported.

## The .iex.exs file

When starting, IEx looks for a local `.iex.exs` file (located in the current working directory), then for a global `.iex.exs` file located inside the directory pointed by the `IEX_HOME` environment variable (which defaults to `~`) and loads the first one it finds (if any).

The code in the chosen `.iex.exs` file is evaluated line by line in the shell's context, as if each line were being typed in the shell. For instance, any modules that are loaded or variables that are bound in the `.iex.exs` file will be available in the shell after it has booted.

Take the following `.iex.exs` file:

    # Load another ".iex.exs" file
    import_file("~/.iex.exs")

    # Import some module from lib that may not yet have been defined
    import_if_available(MyApp.Mod)

    # Print something before the shell starts
    IO.puts("hello world")

    # Bind a variable that'll be accessible in the shell
    value = 13

Running IEx in the directory where the above `.iex.exs` file is located results in:

    $ iex
    Erlang/OTP 24 [...]

    hello world
    Interactive Elixir - press Ctrl+C to exit (type h() ENTER for help)
    iex(1)> value
    13

It is possible to load another file by supplying the `--dot-iex` option to IEx. See `iex --help`.

In case of remote nodes, the location of the `.iex.exs` files are taken relative to the user that started the application, not to the user that is connecting to the node in case of remote IEx connections.

## Configuring the shell

There are a number of customization options provided by IEx. Take a look at the docs for the `IEx.configure/1` function by typing `h IEx.configure/1`.

Those options can be configured in your project configuration file or globally by calling `IEx.configure/1` from your `~/.iex.exs` file. For example:

    # .iex.exs
    IEx.configure(inspect: [limit: 3])

Now run the shell:

    $ iex
    Erlang/OTP 24 [...]

    Interactive Elixir - press Ctrl+C to exit (type h() ENTER for help)
    iex(1)> [1, 2, 3, 4, 5]
    [1, 2, 3, ...]

# Summary

## Functions

break!(ast, stops \\ 1)

Macro-based shortcut for `IEx.break!/4`.

break!(module, function, arity, stops \\ 1)

Sets up a breakpoint in `module`, `function` and `arity` with the given number of `stops`.

color(color, string)

Returns `string` escaped using the specified `color`.

configuration()

Returns IEx configuration.

configure(options)

Configures IEx.

inspect_opts()

Returns the options used for inspecting.

pry()

Pries into the process environment.

started?()

Returns `true` if IEx was started, `false` otherwise.

width()

Returns the IEx width for printing.

# Functions

Link to this macro

# break!(ast, stops \\ 1)

View Source (since 1.5.0) (macro)

Macro-based shortcut for `IEx.break!/4`.

Link to this function

# break!(module, function, arity, stops \\ 1)

View Source (since 1.5.0)

    @spec break!(module(), atom(), arity(), non_neg_integer()) :: IEx.Pry.id()

Sets up a breakpoint in `module`, `function` and `arity` with the given number of `stops`.

This function will instrument the given module and load a new version in memory with line by line breakpoints at the given function and arity. If the module is recompiled, all breakpoints are lost.

When a breakpoint is reached, IEx will ask if you want to `pry` the given function and arity. In other words, this works similar to `IEx.pry/0` as the running process becomes the evaluator of IEx commands and is temporarily changed to have a custom group leader. However, differently from `IEx.pry/0`, aliases and imports from the source code won't be available in the shell.

IEx helpers includes many conveniences related to breakpoints. Below they are listed with the full module, such as `IEx.Helpers.breaks/0`, but remember it can be called directly as `breaks()` inside IEx. They are:

- `IEx.Helpers.break!/2` - sets up a breakpoint for a given `Mod.fun/arity`
- `IEx.Helpers.break!/4` - sets up a breakpoint for the given module, function, arity
- `IEx.Helpers.breaks/0` - prints all breakpoints and their IDs
- `IEx.Helpers.continue/0` - continues until the next breakpoint in the same shell
- `IEx.Helpers.n/0` - goes to the next line of the current breakpoint
- `IEx.Helpers.next/0` - same as above
- `IEx.Helpers.open/0` - opens editor on the current breakpoint
- `IEx.Helpers.remove_breaks/0` - removes all breakpoints in all modules
- `IEx.Helpers.remove_breaks/1` - removes all breakpoints in a given module
- `IEx.Helpers.reset_break/1` - sets the number of stops on the given ID to zero
- `IEx.Helpers.reset_break/3` - sets the number of stops on the given module, function, arity to zero
- `IEx.Helpers.respawn/0` - starts a new shell (breakpoints will ask for permission once more)
- `IEx.Helpers.whereami/1` - shows the current location

By default, the number of stops in a breakpoint is 1. Any follow-up call won't stop the code execution unless another breakpoint is set.

Alternatively, the number of stops can be increased by passing the `stops` argument. `IEx.Helpers.reset_break/1` and `IEx.Helpers.reset_break/3` can be used to reset the number back to zero. Note the module remains "instrumented" even after all stops on all breakpoints are consumed. You can remove the instrumentation in a given module by calling `IEx.Helpers.remove_breaks/1` and on all modules by calling `IEx.Helpers.remove_breaks/0`.

Within a breakpoint, you can call `n` to jump to the next line. To exit a breakpoint, you can either invoke `continue`, which will block the shell until the next breakpoint is found or the process terminates, or invoke `respawn`, which starts a new IEx shell, freeing up the pried one.

## Examples

The examples below will use `break!`, assuming that you are setting a breakpoint directly from your IEx shell. But you can set up a break from anywhere by using the fully qualified name `IEx.break!`.

The following sets up a breakpoint on `URI.parse/1`:

    break! URI, :parse, 1

This call will setup a breakpoint that stops once. To set a breakpoint that will stop 10 times:

    break! URI, :parse, 1, 10

`IEx.break!/2` is a convenience macro that allows breakpoints to be given in the `Mod.fun/arity` format:

    break! URI.parse/1

Or to set a breakpoint that will stop 10 times:

    break! URI.parse/1, 10

This function returns the breakpoint ID and will raise if there is an error setting up the breakpoint.

## Patterns and guards

`IEx.break!/2` allows patterns to be given, triggering the breakpoint only in some occasions. For example, to trigger the breakpoint only when the first argument starts with the "https" string:

    break! URI.parse("https" <> _, _)

Only a single break point can be set per function. So if you call `IEx.break!` multiple times with different patterns, only the last pattern is kept.

## Macros

While it is possible to set breakpoint in macros, remember that macros are generally expanded at compilation time, and therefore they may never be invoked during runtime. Similarly, while patterns may be given to macros, macros receive ASTs as arguments, and not values. For example, if you try to break on a macro with the following pattern:

    break! MyModule.some_macro(pid) when pid == self()

This breakpoint will never be reached, because a macro never receives a PID. Even if you call the macro as `MyModule.some_macro(self())`, the macro will receive the AST representing the `self()` call, and not the PID itself.

## Breaks and `mix test`

To use `IEx.break!/4` during tests, you need to run `mix` inside the `iex` command and pass the `--trace` to `mix test` to avoid running into timeouts:

    $ iex -S mix test --trace
    $ iex -S mix test path/to/file:line --trace

Link to this function

# color(color, string)

View Source

    @spec color(atom(), iodata()) :: iodata()

Returns `string` escaped using the specified `color`.

ANSI escapes in `string` are not processed in any way.

Link to this function

# configuration()

View Source

    @spec configuration() :: keyword()

Returns IEx configuration.

Link to this function

# configure(options)

View Source

    @spec configure(keyword()) :: :ok

Configures IEx.

The supported options are:

- `:colors`
- `:inspect`
- `:width`
- `:history_size`
- `:default_prompt`
- `:continuation_prompt`
- `:alive_prompt`
- `:alive_continuation_prompt`
- `:parser`

They are discussed individually in the sections below.

## Colors

A keyword list that encapsulates all color settings used by the shell. See documentation for the `IO.ANSI` module for the list of supported colors and attributes.

List of supported keys in the keyword list:

- `:enabled` - boolean value that allows for switching the coloring on and off
- `:eval_result` - color for an expression's resulting value
- `:eval_info` - ... various informational messages
- `:eval_error` - ... error messages
- `:eval_interrupt` - ... interrupt messages
- `:stack_info` - ... the stacktrace color
- `:blame_diff` - ... when blaming source with no match
- `:ls_directory` - ... for directory entries (ls helper)
- `:ls_device` - ... device entries (ls helper)

When printing documentation, IEx will convert the Markdown documentation to ANSI as well. Colors for this can be configured via:

- `:doc_code` - the attributes for code blocks (cyan, bright)
- `:doc_inline_code` - inline code (cyan)
- `:doc_headings` - h1 and h2 (yellow, bright)
- `:doc_title` - the overall heading for the output (reverse, yellow, bright)
- `:doc_bold` - (bright)
- `:doc_underline` - (underline)

IEx will also color inspected expressions using the `:syntax_colors` option. Such can be disabled with:

    IEx.configure(colors: [syntax_colors: false])

You can also configure the syntax colors, however, as desired. The below will format atoms in red and remove the coloring for all other data types:

    IEx.configure(colors: [syntax_colors: [atom: :red]])

The default values can be found in `IO.ANSI.syntax_colors/0`.

## Inspect

A keyword list containing inspect options used by the shell when printing results of expression evaluation. Defaults to pretty formatting with a limit of 50 entries.

To show all entries, configure the limit to `:infinity`:

    IEx.configure(inspect: [limit: :infinity])

See `Inspect.Opts` for the full list of options.

## Width

An integer indicating the maximum number of columns to use in output. The default value is 80 columns. The actual output width is the minimum of this number and result of `:io.columns`. This way you can configure IEx to be your largest screen size and it should always take up the full width of your current terminal screen.

## History size

Number of expressions and their results to keep in the history. The value is an integer. When it is negative, the history is unlimited.

## Prompt

This is an option determining the prompt displayed to the user when awaiting input.

The value is a keyword list with two possible keys representing prompt types:

- `:default_prompt` - used when `Node.alive?/0` returns `false`

- `:continuation_prompt` - used when `Node.alive?/0` returns `false` and more input is expected

- `:alive_prompt` - used when `Node.alive?/0` returns `true`

- `:alive_continuation_prompt` - used when `Node.alive?/0` returns `true` and more input is expected

The following values in the prompt string will be replaced appropriately:

- `%counter` - the index of the history
- `%prefix` - a prefix given by `IEx.Server`
- `%node` - the name of the local node

## Parser

This is an option determining the parser to use for IEx.

The parser is a "mfargs", which is a tuple with three elements: the module name, the function name, and extra arguments to be appended. The parser receives at least three arguments, the current input as a string, the parsing options as a keyword list, and the buffer as a string. It must return `{:ok, expr, buffer}` or `{:incomplete, buffer}`.

If the parser raises, the buffer is reset to an empty string.

Link to this function

# inspect_opts()

View Source

    @spec inspect_opts() :: keyword()

Returns the options used for inspecting.

Link to this macro

# pry()

View Source (macro)

Pries into the process environment.

This function is useful for debugging a particular chunk of code when executed by a particular process. The process becomes the evaluator of IEx commands and is temporarily changed to have a custom group leader. Those values are reverted by calling `IEx.Helpers.respawn/0`, which starts a new IEx shell, freeing up the pried one.

When a process is pried, all code runs inside IEx and has access to all imports and aliases from the original code. However, you cannot change the execution of the code nor access private functions of the module being pried. Module functions still need to be accessed via `Mod.fun(args)`.

See also `break!/4` for others ways to pry.

> #### `dbg/0` integration

> By calling `iex --dbg pry`, `iex` will set this function as the default backend for `dbg/0` calls.

## Examples

Let's suppose you want to investigate what is happening with some particular function. By invoking `IEx.pry/0` from the function, IEx will allow you to access its binding (variables), verify its lexical information and access the process information. Let's see an example:

    import Enum, only: [map: 2]

    defmodule Adder do
      def add(a, b) do
        c = a + b
        require IEx; IEx.pry()
      end
    end

When invoking `Adder.add(1, 2)`, you will receive a message in your shell to pry the given environment. By allowing it, the shell will be reset and you gain access to all variables and the lexical scope from above:

    iex(1)> map([a, b, c], &IO.inspect(&1))
    1
    2
    3

Keep in mind that `IEx.pry/0` runs in the caller process, blocking the caller during the evaluation cycle. The caller process can be freed by calling `respawn/0`, which starts a new IEx evaluation cycle, letting this one go:

    iex(2)> respawn()
    true

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

Setting variables or importing modules in IEx does not affect the caller's environment. However, sending and receiving messages will change the process state.

## Pry and macros

When setting up Pry inside a code defined by macros, such as:

    defmacro __using__(_) do
      quote do
        def add(a, b) do
          c = a + b
          require IEx; IEx.pry()
        end
      end
    end

The variables defined inside `quote` won't be available during prying due to the hygiene mechanism in quoted expressions. The hygiene mechanism changes the variable names in quoted expressions so they don't collide with variables defined by the users of the macros. Therefore the original names are not available.

## Pry and `mix test`

To use `IEx.pry/0` during tests, you need to run `mix` inside the `iex` command and pass the `--trace` to `mix test` to avoid running into timeouts:

    $ iex -S mix test --trace
    $ iex -S mix test path/to/file:line --trace

Link to this function

# started?()

View Source

    @spec started?() :: boolean()

Returns `true` if IEx was started, `false` otherwise.

This means the IEx application was started, but not that its CLI interface is running.

Link to this function

# width()

View Source

    @spec width() :: pos_integer()

Returns the IEx width for printing.

Used by helpers and it has a default maximum cap of 80 chars.