Skip to main content

Interactive Shell

Laurence MorganAbout 5 min

Interactive Shell

What's different about Murex's interactive shell?


Aside from Murex being carefully designed with scripting in mind, the interactive shell itself is also built around productivity. To achieve this we wrote our own readline library. Below is an example of that library in use:

asciicastopen in new window

The above demo includes the following features of Murex's bespoke readline library:

  • hint text - blue status text below the prompt (the colour is configurable)
  • syntax highlighting (albeit there isn’t much syntax to highlight in the example). This can also be turned off if your preference is to have colours disabled
  • tab-completion in gridded mode (seen when typing cd)
  • tab-completion in list view (seen when selecting a process name to kill where the process ID was substituted when selected)
  • searching through the tab-completion suggestions (seen in both cd and kill - enabled by pressing [ctrl]+[f])
  • line editing using $EDITOR (vi in the example - enabled by pressing [esc] followed by [v])
  • readline’s warning before pasting multiple lines of data into the buffer and the preview option that’s available as part of the aforementioned warning
  • and VIM keys (enabled by pressing [esc])


Murex uses a custom readline library to enable support for new features in addition to the existing uses you'd normally expect from a shell. It is because of this, Murex provides one of the best user experiences of any of the shells available today.


A full breakdown of supported hotkeys is available in the terminal-keys guide.


Autocompletion happen when you press [tab] and will differ slightly depending on what is defined in autocomplete and whether you use the traditional POSIX pipe token, |, or the arrow pipe, ->.

The | token will behave much like any other shell however -> will offer suggestions with matching data types (as seen in runtime --methods). This is a way of helping highlight commands that naturally follow after another in a pipeline. Which is particularly important in Murex as it introduces data types and dozens of new builtins specifically for working with data structures in an intelligent and readable yet succinct way.

You can add your own commands and functions to Murex as methods by defining them with method. For example if we were to add jq as a method:

method define jq {
    "Stdin":  "json",
    "Stdout": "@Any"

Syntax Completion

Like with most IDEs, Murex will auto close brackets et al.

asciicastopen in new window

Syntax Highlighting

Pipelines in the interactive terminal are syntax highlighted. This is similar to what one expects from an IDE.

Syntax highlighting can be disabled by running:

config set shell syntax-highlighting off


Murex supports inline spellchecking, where errors are underlined. For example

asciicastopen in new window

This might require some manual steps to enable, please see the spellcheck user guide for more details.

Hint Text

The hint text is a (typically) blue status line that appears directly below your prompt. The idea behind the hint text is to provide clues to you as type instructions into the prompt; but without adding distractions. It is there to be used if you want it while keeping out of the way when you don't want it.

Configuring Hint Text Colour

By default the hint text will appear blue. This is also customizable:

» config get shell hint-text-formatting

The formatting config takes a string and supports ANSI constants.

It is also worth noting that if colour is disabled then the hint text will not be coloured even if hint-text-formatting includes colour codes:

» config set shell color false

(please note that syntax highlighting is unaffected by the above config)

Custom Hint Text Statuses

There is a lot of behavior hardcoded into Murex like displaying the full path to executables and the values of variables. However if there is no status to be displayed then Murex can fallback to a default hint text status. This default is a user defined function. At time of writing this document the author has the following function defined:

config set shell hint-text-func {
    trypipe <!null> {
        git status --porcelain -b -> set gitstatus
        $gitstatus -> head -n1 -> regexp 's/^## //' -> regexp 's/\.\.\./ => /'
    catch {
        out "Not a git repository."

...which produces a colorized status that looks something like the following:

develop => origin/develop

Starship Example

The following screenshot is of a custom hint text using Starship:

Source: in new window

Disabling Hint Text

It is enabled by default but can be disabled if you prefer a more minimal prompt:

» config set shell hint-text-enabled false


Murex supports a couple of full screen preview modes:

Autocomplete Preview

Enabled via [f1]

This displays a more detailed view of each parameter you're about to pass to a command, without you having to run that command nor leave the half-completed command line.

It can display:

  • man pages
  • custom guides like
  • information about binary files
  • contents of text files
  • and even images too!

Command Line Preview

Enabled via [f9]

The Command Line Preview allows you to view the output of a command line while you're still writing it. This interactivity removes the trial-and-error from working with complicated command line incantations. For example parsing parsing complex documents like machine generated JSON becomes very easy.

This does come with some risks because most command line operations change you systems state. However Murex comes with some guardrails here too:

  • Each command in the pipeline is cached. So if a command's parameters are changed, Murex only needs to re-run the commands from the changed parameter onwards.

  • Each time there is a change in the commands themselves, for example a new command added to the pipeline, you are requested to press [f9] to re-run the entire pipeline.

  • The only commands considered "safe" for auto-execution if any parameters do change are those marked as "safe" in config. For example:

    » config get shell safe-commands -> tail -n5

Safer Pasting

A common behaviour for command line users is to copy and paste data into the terminal emulator. Some shells like Zsh support Bracketed pasteopen in new window but that does a pretty poor job of protecting you against the human error of pasting potentially dangerous contents from an invisible clipboard.

Where Murex differs is that any multi-line text pasted will instantly display a warning prompt with one of the options being to view the contents that you're about to execute.

This gives you piece-of-mind that you are executing the right clipboard content rather than something else you copied hours ago and forgotten about.

Smarter Error Messages

Errors messages in most shells suck. That's why Murex has taken extra care to give you as much useful detail as it can.

See Also

  • ANSI Constants: Infixed constants that return ANSI escape sequences
  • Code Block Parsing: Overview of how code blocks are parsed
  • Spellcheck: How to enable inline spellchecking
  • Terminal Hotkeys: A list of all the terminal hotkeys and their uses
  • -> Arrow Pipe: Pipes STDOUT from the left hand command to STDIN of the right hand command
  • autocomplete: Set definitions for tab-completion in the command line
  • config: Query or define Murex runtime settings
  • method: Define a methods supported data-types
  • runtime: Returns runtime information on the internal state of Murex
  • { Curly Brace }: Initiates or terminates a code block
  • | POSIX Pipe: Pipes STDOUT from the left hand command to STDIN of the right hand command

This document was generated from gen/user-guide/interactive-shell_doc.yamlopen in new window.

Last update:
Contributors: Laurence Morgan,Laurence Morgan,Olivier Refalo