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Moulti documentation


This document assumes: - you have read Moulti's README file; - you have a vague idea of what Moulti is and how it could become useful to you; - you are comfortable with the command line on Unix and/or Unix-like operating systems.

Technical requirements (abridged)

Moulti requires: - Linux, BSD or MacOS - Python ≥ 3.10 - Textual ≥ 0.53


Moulti is available as a Python package on PyPI and can thus be installed using pip or, more conveniently, pipx:

pipx install moulti
pipx ensurepath

Distribution packages are of course welcome.

Shell Completion

Moulti is compatible with argcomplete global completion. This means that, depending on your system and installed packages, shell completion for Moulti may work out of the box. This should be true for:

  • Debian (bash, but also zsh)
  • Fedora (bash only)

... as long as packages bash-completion and python3-argcomplete are installed.

Otherwise, refer to the argcomplete documentation.

Limitation: shell completion will help typing subcommands and options but is technically unable to suggest existing step names.

First steps with Moulti

  1. Open two terminals on the same machine/host/VM/container.
  2. In the first terminal, launch the Moulti instance, i.e. the Terminal User Interface (TUI) itself: shell TERM=xterm-256color moulti init Upon startup, Moulti is empty: it shows nothing beyond a title bar and a footer: step 2
  3. From now on, we will use the second terminal to issue commands to the Moulti instance through the Command-Line Interface (CLI) client. First, make yourself at home by setting its title: shell moulti set --title='This is MY (first) Moulti instance' The effect should be immediate in the first terminal: step 3
  4. Create your first Moulti step with step id "my_step": shell moulti step add my_step --title='My first step' step 4
  5. Now, fill the "log" part of your step with some content: shell ip -c a | moulti pass my_step Again, the effect should be immediate in the first terminal: step 5
  6. Back to the second terminal, adjust your step: shell moulti step update my_step --classes='success' moulti step update my_step --top-text='Here is the output of [red bold]ip -color address[/]:' step 6
  7. That syntax we used to turn the command red is called "Rich markup"; its BBcode-like syntax is described here, the list of available colors is there and styles that typically work fine in a modern terminal emulator are: blink bold conceal italic overline reverse strike underline underline2. Try them all at once: shell moulti step update my_step --bottom-text='[blink]blink[/] [bold]bold[/] [conceal]conceal[/] [italic]italic[/] [overline]overline[/] [reverse]reverse[/] [strike]strike[/] [underline]underline[/] [underline2]underline2[/] [blue]blue[/] [on yellow1]on yellow1[/] [blue on yellow1]blue on yellow1[/]' step 7

Refer to the output of moulti step add --help for more options.

Important: Rich markup cannot be used in the log part of a step.

  1. And of course, you can add multiple such steps: shell for class in warning error standard; do moulti step add "${class}_example" \ --classes="${class}" \ --title="${class^} step" \ --text="This is a step with class '${class}'." \ --bottom-text=' ' done step 8

Just keep this constraint in mind: step ids (e.g. "my_step") must remain unique in a Moulti instance. 9. If necessary, you can also clear (i.e. empty) a step: shell moulti step clear warning_example or simply delete it: shell moulti step delete error_example step 9

Shell scripting

The key takeaway from the previous section is that Moulti starts as an empty shell that is meant to be controlled and filled through the moulti CLI tool. A simple Moulti-based bash script makes use of two new commands:

  • moulti run: same as moulti init but runs a command right after the startup phase
  • moulti wait: tries connecting to the Moulti instance; think "ping for moulti"

... and looks like this:

#!/usr/bin/env bash

# Name the Moulti instance to prevent conflicts:
export MOULTI_INSTANCE='my-first-script-with-moulti'
# If not done already, start a Moulti instance and have it re-execute this script:
[ "${MOULTI_RUN}" ] || exec moulti run -- "$0" "$@"
# Ensure the Moulti instance is reachable:
moulti wait
moulti step add step_1 --title='First step'
   echo "$(date --iso-8601=ns) Starting combobulating things and stuff..."
   # your stuff here
} 2>&1 | moulti pass step_1
moulti step add step_2 --title='Second step'
   echo "$(date --iso-8601=ns) Ensure things and stuff were properly combobulated..."
   # more stuff there
} 2>&1 | moulti pass step_2

In practice, it makes sense to heavily leverage shell functions, such as those available in moulti-functions.bash.

moulti run: dealing with stdin, stdout, stderr

By default, scripts launched through "moulti run":

  • have their standard input (stdin, file descriptor #0) redirected to /dev/null;
  • inherit the standard and error outputs (stdout and stderr, file descriptors #1 and #2) from Moulti (e.g. /dev/pts/42);
  • should not try to read from stdin;
  • should either refrain from writing to stdout/stderr or...
  • should redirect stdout/stderr to a suitable destination.

Possible approaches in bash:

# Discard stdout and stderr entirely:
exec > /dev/null 2>&1

# Log stdout and stderr to a custom log file:
exec > custom.log 2>&1

# Pass stdout and stderr to a dedicated Moulti step:
moulti step add main_script_output
exec > >(moulti pass main_script_output) 2>&1

# Pass stdout and stderr to a dedicated Moulti step but keep a copy in a custom log file:
moulti step add main_script_output
exec > >(tee --append custom.log | moulti pass main_script_output) 2>&1

If, for some reason, the recommendations above cannot be applied, the environment variable MOULTI_RUN_OUTPUT should help: - MOULTI_RUN_OUTPUT=discard redirects stdout and stderr to /dev/null, thus discarding any unexpected output; - MOULTI_RUN_OUTPUT=harvest harvests stdout and stderr lines and passes them to the moulti_run_output step; - any other value leads to the default behaviour: stdout and stderr are left untouched and their output is liable to degrade Moulti's visual display.

The moulti_run_output step is special in that it is created upon reception of the first byte of output if it does not exist already. It can be created beforehand, can be updated or cleared at any time and cannot be deleted while the script is running.

moulti run: dealing with ssh

SSH clients and SSH-based tools (e.g. Ansible) sometimes need user input, e.g. to accept a new host key or enter a passphrase/password. By default, these interactions happen not over stdin but rather over the current TTY... resulting in a messy conflict with Moulti.

This issue is usually addressed by configuring SSH clients so they use a separate "askpass" program for user interactions. Moulti provides such a program: moulti-askpass.

Try out moulti-askpass on its own:

# First terminal:
MOULTI_INSTANCE=trying-moulti-askpass moulti init

# Second terminal:
export MOULTI_INSTANCE=trying-moulti-askpass
moulti-askpass 'Tell me a secret:'
SSH_ASKPASS_PROMPT=confirm moulti-askpass 'If you can read this, then moulti-askpass works fine'
SSH_ASKPASS_PROMPT=none moulti-askpass 'If you can read this, then moulti-askpass works fine'

The OpenSSH client can be configured to use moulti-askpass by setting two environment variables:

export SSH_ASKPASS=moulti-askpass

moulti run automatically sets these variables IF SSH_ASKPASS is not set already. Consequently, SSH clients and SSH-based tools should work out of the box with moulti run.

moulti run: dealing with git

Like SSH, Git may require user input. Fortunately, it uses SSH_ASKPASS to do so.

Consequently, Git should work out of the box with moulti run. If necessary, explicitly set GIT_ASKPASS in your scripts to bypass the core.askPass configuration variable:


moulti run: dealing with sudo

Like SSH, sudo may require user input. Like SSH, sudo supports askpass programs: it requires:

  • running sudo -A or sudo --askpass instead of sudo
  • setting a single environment variable: export SUDO_ASKPASS=$(which moulti-askpass)

Note that sudo does not perform $PATH lookup, so SUDO_ASKPASS must be a path (either absolute or relative).

moulti run automatically sets SUDO_ASKPASS IF it is not set already AND moulti-askpass exists in $PATH. Consequently, sudo should work out of the box with moulti run.

moulti run: dealing with Ansible

According to their homepage, Ansible is "an IT automation engine that automates provisioning, configuration management, application deployment, orchestration, and many other IT processes". In practice, Ansible users run ansible-playbook commands that output a succession of results grouped by task.

Ansible uses a plugin architecture to enable a rich, flexible and expandable feature set so Moulti provides an stdout callback plugin. When loaded and executed by ansible-playbook, this plugin runs moulti commands that display the results of each Ansible task in a separate Moulti step.

In practice, combining Ansible with Moulti is as simple as:

moulti run -- ansible-playbook your-playbook.yaml

Under the hood, moulti run performs some magic. It sets two environment variables: - ANSIBLE_STDOUT_CALLBACK: id of the stdout callback plugin to use: moulti - ANSIBLE_CALLBACK_PLUGINS: colon-separated list of paths that Ansible searches for callback plugins. If this environment variable is set already, moulti simply appends its own plugin path to it.

However, unlike SSH and sudo, this integration is not always desirable so moulti run relies on the following heuristics: - If the environment variable MOULTI_ANSIBLE is set to force, it systematically sets both environment variables. - If the environment variable MOULTI_ANSIBLE is set to no, it sets neither. - Otherwise, it sets both environment variables if the name of the executed program contains ansible AND ANSIBLE_STDOUT_CALLBACK is not set already.

If you feel confused, experiment with moulti run --print-env:

  1. Forbid Ansible-Moulti integration:
$ MOULTI_ANSIBLE=no moulti run --print-env -- ansible-playbook your-playbook.yaml | grep ^ANSIBLE
  1. Enforce Ansible-Moulti integration:
$ MOULTI_ANSIBLE=force moulti run --print-env -- | grep ^ANSIBLE
  1. Leverage the heuristics:
$ moulti run --print-env -- ansible-playbook your-playbook.yaml | grep ^ANSIBLE
$ moulti run --print-env -- | grep ^ANSIBLE
$ moulti run --print-env -- | grep ^ANSIBLE

Tips: - Depending on its verbosity level (from -v to -vvvvv), Ansible is liable to output lines before Moulti's stdout callback plugin is invoked. Therefore, it is recommended to set MOULTI_RUN_OUTPUT=harvest. - By default, the callback plugin changes the title of the Moulti instance; set the environment variable MOULTI_ANSIBLE_NO_TITLE to any value to prevent that.

Python scripting

Python scripting may be achieved by importing the moulti.protocol module and getting some inspiration from the moulti.cli module.

Example 1: create and fill a new step from a string through two separate connections:

from moulti.protocol import send_to_moulti
add_step_msg = {'command': 'step', 'action': 'add', 'id': 'python', 'title': 'Step created from Python', 'collapsed': False}
generated_text = '\n'.join(['Python made this: ' + chr(i)*62 for i in range(33, 127)])
set_text_msg = {'command': 'step', 'action': 'update', 'id': 'python', 'text': generated_text}

Example 2: create and fill a new step through a single connection:

from moulti.protocol import moulti_connect, send_json_message, recv_json_message
filepath = '/etc/passwd'
with moulti_connect() as moulti_socket:
    add_step_msg = {'command': 'step', 'action': 'add', 'id': 'python', 'title': f'{filepath}:', 'collapsed': False}
    send_json_message(moulti_socket, add_step_msg)
    with open(filepath) as filedesc:
        pass_fd_msg = {'command': 'pass', 'id': 'python'}
        send_json_message(moulti_socket, pass_fd_msg, [filedesc.fileno()])

Warning: Moulti is a young project and currently offers no guarantee whatsoever regarding the stability and availability of Python modules and functions.

Multiple ways to fill a step

As you probably noticed already, there are multiple ways to fill a Moulti step: - moulti pass my_step is the recommended way as, unlike other methods, it is not limited by the maximum amount of text you can pass through command-line arguments - moulti step add my_step --text=$'line1\nline2\nline3' is suitable to fill steps as soon as they appear in Moulti - moulti step update my_step --text=$'line1\nline2\nline3' is the same but applies to existing steps - moulti step append my_step 'line1' 'line2' 'line3' complements add --text and update --text, which both imply to provide the output as a single argument; note: it may be necessary to step clear beforehand.

All methods above share one common limitation: it is not possible to append partial lines to Moulti steps. Conversely, lines will not show up in Moulti until they are terminated with a line feed (LF / \n) character.

Multiple ways to display steps

By default, Moulti displays steps at the top of the screen and adds new steps below existing steps.

This behavior can be changed through moulti set:

  • moulti set --step-position=bottom displays steps at the bottom of the screen
  • moulti set --step-position=top displays steps at the top of the screen
  • moulti set --step-direction=up displays steps from last to first (new steps are added above existing steps)
  • moulti set --step-direction=down displays steps from first to last (new steps are added below existing steps)

Interact with end users through questions

Sometimes, it is necessary to prompt the user for a confirmation, a value or an option. Since Moulti occupies the entirety of the terminal and its standard input, it is no longer possible to use shell features such as read. This is why Moulti provides questions. Questions are special steps the sole purpose of which is to display interactive components such as buttons or input fields. Here is how to use them:

  1. Creating a question is not very different from creating a regular step: shell moulti inputquestion add my_first_question \ --title='My first question with Moulti' \ --text='What is your name?' \ --bottom-text='We want information... information... information!' \ --placeholder='Please enter your name in this input field' step 1
  2. Getting the answer is straightforward: console $ moulti inputquestion get-answer my_first_question --wait Alice $ Notes:
  3. Once the answer is submitted, the question's interactive components are disabled. This prevents users from submitting multiple answers for a single question.
  4. Feel free to read moulti inputquestion add --help to get more control on what users can type in the input field.
  5. Moulti also supports buttons through buttonquestion steps. shell moulti buttonquestion add my_second_question \ --title='My second question with Moulti' \ --text='What is your name?' \ --bottom-text='What a mess:' \ --button alice success Alice \ --button bob primary Bob \ --button craig default Craig \ --button mallory error Mallory \ --button oscar warning Oscar

step 3

Each button is defined by exactly three items: - value: the value returned by get-answer - style: default, primary, error, warning, or success - label: what the button should display

Known limitations: - Buttons cannot be changed through moulti buttonquestion update.

  1. Again, getting the answer is straightforward: console $ moulti buttonquestion get-answer my_second_question --wait craig $


Dividers are simplistic steps that exist solely for cosmetic purposes, like displaying static text or acting as visual separator between two groups of steps (hence the name). Unlike other steps, they are not collapsible.

moulti divider add my_first_divider --title=$'This text is simply displayed.\nMulti-line is possible. So is [i]rich formatting[/]'
moulti divider update my_first_divider --classes=warning
moulti divider delete my_first_divider

Progress bar

Moulti offers an optional progress bar, which appears at the bottom of the screen, just above the footer (and above the console if it is visible). Like everything else in Moulti, the progress bar is strictly CLI-driven, which means Moulti will never set, move, update, or configure the progress bar by itself.

Moulti's progress bar being entirely optional, it is hidden by default:

# Show the progress bar:
moulti set --progress-bar
# Hide the progress bar:
moulti set --no-progress-bar

The progress bar displays a percentage on its right side. That percentage is computed based on progress and progress-target values. For instance, this command results in a "20%" progress bar:

moulti set --progress=1138 --progress-target=5555

However, by default, none of these values are set and Moulti shows an "indeterminate" progress bar until progress-target is set. It is possible to force the display of such a progress bar by setting a negative or zero progress-target:

moulti set --progress-target=0
moulti set --progress-target=-1
moulti set --progress-target=-2.718281828459045

When updating the progress bar, it is possible to use either absolute or relative values:

moulti set --progress 80
moulti set --progress +1
moulti set --progress +20
# Going backward is allowed:
moulti set --progress -5

Refer to progressbar.bash for a demonstration of the typical use case.

Saving your stuff

Saving a complete Moulti instance

Click Save or hit s in Moulti to export (almost) all shown contents to text files. Specifically, Moulti creates a new directory named after the instance (MOULTI_INSTANCE environment variable) and the current date and time. This export directory is created in the directory specified by the MOULTI_SAVE_PATH environment variable or, alternatively, in Moulti's current working directory.

The format is straightforward: - each step is exported as a JSON file reflecting its properties and a log file reflecting its contents; - an extra JSON file stores instance properties.

$ ls -al social-preview-2024-02-23T18-52-10.883600/
-rw-r--r-- 1 user group   61 2024-02-23 18:52:10
-rw-r--r-- 1 user group 1.8K 2024-02-23 18:52:10 1-title.contents.log
-rw-r--r-- 1 user group  394 2024-02-23 18:52:10
-rw-r--r-- 1 user group  554 2024-02-23 18:52:10 2-step_ping.contents.log
-rw-r--r-- 1 user group  376 2024-02-23 18:52:10
-rw-r--r-- 1 user group   34 2024-02-23 18:52:10 3-collapsed.contents.log
-rw-r--r-- 1 user group  310 2024-02-23 18:52:10
-rw-r--r-- 1 user group 9.3K 2024-02-23 18:52:10 4-script.contents.log
-rw-r--r-- 1 user group  273 2024-02-23 18:52:10
-rw-r--r-- 1 user group  567 2024-02-23 18:52:10

Limitations: - if an inputquestion was configured with --password, then its export will contain a series of * characters instead of its actual value. - Moulti does not tinker with file permissions; therefore, the resulting files have default ownership and permissions; if necessary, use e.g. umask or newgrp to alter its behavior.

Saving a single Moulti step

Hit c to copy the contents of the currently focused step to the clipboard. Hit w to do the same while preserving styles and colors (as ANSI escape codes). Moulti emits a notification reflecting whether the copy operation succeeded. Copy operations typically fail due to environment-related causes. The pyperclip documentation states most of the technical requirements:


Restoring your stuff

Here is the typical way to restore a Moulti instance:

MOULTI_INSTANCE=social-preview-restored moulti run moulti load social-preview-2024-02-23T18-52-10.883600/

Explanations: moulti run moulti load is NOT a typo. The command above: 1. starts a new Moulti instance named "social-preview-restored" -- the naming is optional but prevents clashes with any other instance; 2. run asks the instance to run a command; here, this command is not a script but... 3. moulti load path/to/saved/directory, i.e. a Moulti CLI command that reads the contents of the given directory and loads it into the Moulti instance.

moulti diff

moulti diff is a variant of moulti load specialized in loading diff files into Moulti.

Important: moulti diff only supports the unified diff format.

Here is how to use it:

# Terminal #1: launch a Moulti instance
moulti init

# Terminal #2:
#  Example 1: load a diff file:
moulti diff parse /path/to/example.diff

# Example #2: get diff data from an external command through a pipe:
diff -u /etc/passwd /etc/passwd- | moulti diff parse /dev/stdin

#  Example #3: the same without a pipe:
moulti diff run -- diff -u /etc/passwd /etc/passwd-

Like moulti load, moulti diff can be combined with moulti run:

# Load a diff file:
moulti run -- moulti diff parse /path/to/examples.diff

#  Example #3: the same without a pipe:
moulti run -- moulti diff run -- git -C /path/to/git/working/directory show


By default, moulti diff reads diff data as UTF-8 text; this encoding can be changed by setting the environment variable MOULTI_DIFF_ENCODING, e.g. export MOULTI_DIFF_ENCODING=iso-8859-1.


By default, moulti diff changes the title of the Moulti instance; set the environment variable MOULTI_DIFF_NO_TITLE to any value to prevent that.

Moulti does not...

Per se, Moulti does not:

  • number lines (use e.g. nl -ba or cat -n)
  • timestamp lines (use e.g. ts '%FT%T%z' from the moreutils package)
  • perform syntax highlighting (use e.g. bat / batcat or rich)
  • wrap lines (use e.g. fold)
  • distinguish stdout from stderr (it reads a single stream anyway; use e.g. stderred)
  • tweak the output buffering policy of other processes:
  • look for command-line options and environment variables that explicitly address the issue, e.g. --line-buffered or PYTHONUNBUFFERED=1
  • use LD_PRELOAD-based tools such as stdbuf or cvolny/faketty
  • use tools that allocate a pty, e.g. script or dtolnay/faketty: bash script --quiet --return --command 'your command here' /dev/null | moulti pass your_step
  • trick other processes into outputting colors or emojis:
  • look for command-line options and environment variables that explicitly address the issue, e.g. --color=always or FORCE_COLOR=1
  • use LD_PRELOAD-based tools such as cvolny/faketty
  • use tools that allocate a pty, e.g. script or dtolnay/faketty
  • strip colors from input:
  • look for command-line options and environment variables that explicitly address the issue, e.g. --color=never or NO_COLOR=1
  • use tools to strip ANSI escape codes, e.g. ansi2txt from colorized-logs
  • keep track of when your processes started, how long they ran and/or what return code they exited with... but see moulti_exec in moulti-functions.bash for an example of it.

All of this can be achieved from the controlling script.

Moulti does not... yet

These features may appear in future versions: - type feature, for animation purposes.

moulti pass: setting read size

As these lines are being written, Moulti's performance has room for improvement. Consequently, commands that quickly output numerous lines (e.g. find / -ls) will seem like they keep piping output to Moulti whereas they have exited already.

If you know in advance a command is going to output numerous lines, you can tweak the way Moulti will read them:

# The default behaviour is fine when one needs to display each line as soon as possible:
ping | moulti pass my_step

# This outputs 45,000+ lines, so increase read size significantly:
find /sys -ls | moulti pass my_step --read-size=131072

On the other hand, if you absolutely want to see the very latest line output by a process, ensure --read-size is not set or explicitly force it to --read-size=1.

moulti pass: gotchas

The typical use of moulti pass is some_command | moulti pass my_step. However, it is also possible to invoke moulti pass my_step directly. In this case, each line you type in your terminal will end up in Moulti after you hit Enter, and this is the expected behavior. But beware: hitting Ctrl+c or Ctrl+z will act as expected on the moulti client process... BUT the Moulti instance still holds a file descriptor to your terminal's standard input and still reads from it. This essentially breaks your current terminal (with the Moulti instance eating up about half the characters you type) until you: 1. quit the Moulti instance (just hit q) 2. send Ctrl+d in the affected terminal.

The correct way to use moulti pass interactively is to signal the end of file through Ctrl+d.

$ moulti pass my_step
1st line<enter>
2nd line<enter>
n-th line<enter>
last line<enter>


Manually scrolling through steps

You can scroll through steps: - by grabbing the main scrollbar handle using the mouse pointer; - using the mouse wheel (or its laptop equivalent) -- tip: ensure the cursor is not over a scrollable step log part; - by hitting the Up, PgUp, Home or End key -- tip: ensure the focus is not held by a step log part.

If moulti is already scrolling through steps automatically (see next section Programmatically scrolling through steps), but you want to read a part of the output while the job is still running, hit l or click "L Lock scroll" in the footer to prevent programmatic scrolling from interfering with your actions.

The main scrollbar handle turns green to indicate that the lock is enabled and automatic scrolling is disengaged.

Programmatically scrolling through steps

moulti scroll

Use moulti scroll step_name to make Moulti scroll to a given step. If this step cannot be displayed entirely, moulti scroll will display its upper part.

It is possible to define which line of the step should absolutely be displayed by specifying an offset as second argument. Important: here, a line does not mean a line of the text output shown by the chosen step but rather one of the lines that make up the entire chosen step on screen.

# Ensure the first line of the step is displayed:
moulti scroll step_name 0
# Ensure the second line of the step is displayed:
moulti scroll step_name 1
# Ensure the third line of the step is displayed:
moulti scroll step_name 2

# Ensure the last line of the step is displayed:
moulti scroll step_name -1
# Ensure the second to last line of the step is displayed:
moulti scroll step_name -2

It often makes sense to call moulti scroll after adding an interactive step (buttonquestion, inputquestion).

Scroll on activity

Sometimes, it is desirable to make a step visible when a new line of output shows up. This can be achieved using --scroll-on-activity:

# By default, steps do not scroll on activity:
moulti step add foo --bottom-text=' ' --title='Your shiny title here'
moulti pass foo <<< 'do not scroll'

# Enable scroll on activity:
moulti step update foo --scroll-on-activity=true
# Try it:
moulti pass foo --append <<< 'scroll!'

# A typical use case is to ensure the last line of output is displayed:
moulti step update foo --max-height=0 --scroll-on-activity=-1
# Try it:
yes 'scroll to the last line!' | nl -ba | head -500 | moulti pass foo --append

# Disable scroll on activity:
moulti step update foo --scroll-on-activity=false
moulti pass foo --append <<< 'do not scroll!'

Manually scrolling inside steps

By default, Moulti strives to display the latest lines it received and thus keeps scrolling down as long as lines keep coming. This constant scrolling stops as soon as you scroll up: - using the mouse wheel (or its laptop equivalent); - by grabbing the scrollbar handle using the mouse pointer; - by hitting the Up, PgUp or Home key.

The constant scrolling resumes when you hit the End key.

Programmatically scrolling inside steps

Moulti currently offers no suport for programmatic scrolling inside steps.

Environment variables

Environment variables you may set


  • MOULTI_INSTANCE: name of your Moulti instance; defaults to default; taken into account by the instance to compute the default value of MOULTI_SOCKET_PATH.
  • MOULTI_SOCKET_PATH: path to the network socket that Moulti should listen/connect to; taken into account by both the instance and the CLI; if not specified, Moulti defaults to a platform-specific value that reflects your username and MOULTI_INSTANCE; examples: @moulti-bob-test-instance.socket, /run/user/1000/moulti-bob-test-instance.socket.
  • MOULTI_ALLOWED_UID: abstract sockets (i.e. Linux) only! By default, Moulti only accepts commands from the user (uid) that launched the Moulti instance; setting this environment variable beforehand makes it accept arbitrary uids; example: shell export MOULTI_ALLOWED_UID="1001,1002,5000,$(id -u alice),$(id -u bob)" moulti init
  • MOULTI_ALLOWED_GID: abstract sockets (i.e. Linux) only! By default, Moulti only accepts commands from the user (uid) that launched the Moulti instance; setting this environment variable beforehand makes it accept arbitrary gids; example: shell export MOULTI_ALLOWED_GID=141 moulti init
  • MOULTI_PASS_CONCURRENCY: define how many concurrent "moulti pass" commands is acceptable; defaults to 20.

Appearance, look and feel

  • MOULTI_MODE: light to start Moulti in light mode, dark to start Moulti in dark mode; defaults to dark.
  • MOULTI_ANSI: define whether and how Moulti alters the 16 standard ANSI colors. There are three available policies:
  • verbatim: (default value since v1.5.0) ANSI colors appear the same way inside Moulti as outside Moulti. However, Moulti does not try to guess the background and foreground colors of your terminal. That may affect readability. If needed, you can specify them using this syntax: MOULTI_ANSI=verbatim:darkbg=000000,darkfg=e6e6e6,lightbg=ffaaff,lightfg=000000 # darkbg: background color in dark mode; default value: #0c0c0c # darkfg: foreground color in dark mode; default value: #d9d9d9 # lightbg: background color in light mode; default value: #f7f7f7 # lightfg: foreground color in light mode; default value: #000000 The order of these attributes does not matter and you do not have to specify all of them unless actually needed. Therefore, MOULTI_ANSI=verbatim and MOULTI_ANSI=verbatim: work fine.
  • theme:dark=theme_name1,light=theme_name2: define what ANSI themes to use in dark and light modes; specifying one theme for each mode is usually enough; if needed, specify multiple themes separated by : so that Moulti picks the first one it knows about.

    Built-in themes include: DEFAULT_TERMINAL_THEME, MONOKAI, DIMMED_MONOKAI, NIGHT_OWLISH, SVG_EXPORT_THEME. - textual_default: let the Textual framework handle ANSI colors (default behavior before v1.5.0). In practice, Textual uses built-in themes: - MONOKAI in dark mode - ALABASTER in light mode

    Therefore, MOULTI_ANSI=textual_default means the same as MOULTI_ANSI=theme:dark=MONOKAI,light=ALABASTER. - MOULTI_ANSI_THEME_*: define your own ANSI themes; examples: shell # 16-color theme: MOULTI_ANSI_THEME_Kibble=bg=0E100A,fg=F7F7F7,ansi=4D4D4D:C70031:29CF13:D8E30E:3449D1:8400FF:0798AB:E2D1E3:5A5A5A:F01578:6CE05C:F3F79E:97A4F7:C495F0:68F2E0:FFFFFF # 8-color theme: specified colors are used as both regular and bright colors: MOULTI_ANSI_THEME_halfvga=bg=000000,fg=AAAAAA,ansi=000000:AA0000:00AA00:AA5500:0000AA:AA00AA:00AAAA:AAAAAA Manually defining MOULTI_ANSI_THEME_* can be painful. So have a look at this helper script that turns Gogh themes into such variables: shell tools/gogh2moulti.bash Important: - Setting MOULTI_ANSI_THEME_* defines a Moulti theme but does not use it; to use it, set MOULTI_ANSI. - Theme names are case-sensitive: if you define MOULTI_ANSI_THEME_AlphaBeta, be sure to mention e.g. MOULTI_ANSI=dark=AlphaBeta, not MOULTI_ANSI=dark=ALPHABETA. - MOULTI_CUSTOM_CSS: absolute filepath to a custom TCSS file; see "How to define my own step classes ?"

About colors in MOULTI_ANSI*: - colors may be prefixed with #; - hexadecimal digits may be specified as lower or uppercase but there must be exactly 6 digits.


  • MOULTI_ANSIBLE_NO_TITLE to prevent the Ansible plugin from changing the title of the Moulti instance
  • MOULTI_DIFF_NO_TITLE to prevent moulti diff from changing the title of the Moulti instance


Environment variables set by the Moulti instance

These variables are set by the Moulti instance when it runs a script, e.g. moulti run -- my_script.bash:

  • MOULTI_RUN: its value is irrelevant but its mere presence means your script should NOT try to spawn a new Moulti instance.
  • MOULTI_INSTANCE_PID: process id of the Moulti instance, in case your script needs to act upon the Moulti process itself.
  • MOULTI_SOCKET_PATH: described in the previous section; the Moulti instance explicitly sets this variable to ensure your script can connect to it.

Additionally, Moulti may set variables so other tools integrate into Moulti:

Such variables may or may not be set depending on criteria like existing environment variables or the command-line. If you feel confused and want to investigate the matter, run moulti run --print-env -- your command here. Example:

$ moulti run --print-env -- true

Other environment variables

  • TERM: per se, Moulti does nothing with this environment variable. However, $TERM has a strong influence on the behavior and visual aspect of curses applications and Moulti is no exception. Your mileage may vary but, overall, it seems TERM=xterm-256color frequently fix things.
  • NO_COLOR: if present, convert the application to monochrome; this variable comes from the Textual framework.

How to define my own step classes ?

Out of the box, Moulti provides four step classes: - standard (blue) - success (green) - warning (orange) - error (red)

Here, "class" is a synonym for "style" or "color" and actually refers to the notion of CSS class. Moulti is based on the Textual framework, which borrows various principles from the world of web design, starting with their own variant of CSS: Textual CSS (TCSS).

Moulti embeds its TCSS inside its Python code but allows end users to redefine whatever they see fit through a TCSS file of theirs, the path of which should be passed through the MOULTI_CUSTOM_CSS environment variable.

The snippets below demonstrate how to leverage this mechanism to define one's step classes and change the colors of the Moulti header.


/* Define a step class named "customstate" rendered with red text on a yellow background: */
Step.customstate {
    color: red;
    background: yellow;
    & MoultiLog { scrollbar-corner-color: yellow; }

/* Customise steps shown by moulti-askpass: */
.askpass {
    color: gray;
    background: black;
    padding: 2;
    border: panel blue;

/* Change the colors of the Moulti header: */
#header {
    background: red;
    color: yellow;
MOULTI_CUSTOM_CSS=/path/to/moulti-custom.tcss moulti init

Caution: if the MOULTI_CUSTOM_CSS environment variable is set, the path it indicates must exist and point to a syntactically valid TCSS file or the Moulti instance will crash.

Technical requirements (unabridged)

Moulti requires a Unix-friendly operating system. Specifically, it requires an operating system that implements AF_UNIX+SOCK_STREAM local network sockets. Microsoft Windows does implement such sockets but the Python interpreter does not expose this feature to applications yet. Progress on this matter ought to happen through Python issue #77589. Once this issue is resolved, porting Moulti to Microsoft Windows should become possible.

Moulti requires Python ≥ 3.10 because:

  • Moulti leverages Textual, which requires Python 3.8 or later.
  • Moulti uses send_fds and recv_fds, which require Python ≥ 3.9.
  • Tests using Python 3.9.18 almost immediately hit blocking issues, specifically:
  • steps not reacting to keyboard/mouse events ;
  • Task got Future <Future pending> attached to a different loop Python exception.
  • Python 3.9 isn't receiving regular bug fixes anymore.
  • Moulti type hints use PEP 604 (Allow writing union types as X | Y) syntax, which requires Python ≥ 3.10.

The minimum version of Textual required to run Moulti is 0.53. Details: - version 0.53.0 exposes ANSI themes - version 0.47.0 was the minimum requirement before the implementation of ANSI themes - version 0.46.0 fails with message "Error in stylesheet" - version 0.24.0 fails with message "ImportError: Package 'textual.widgets' has no class 'Collapsible'" - version 0.1.13 fails with message "ImportError: cannot import name 'work' from 'textual'"


This section exposes various reflections that contributed to the architectural design of Moulti.

Moulti is a CLI-driven TUI. This implies that a (relatively) long-running process takes care of maintaining and updating the TUI while (relatively) short-running processes send instructions about what to update. To this end, CLI processes need a protocol to communicate with the TUI instance.

In the end, Moulti is architected around 5 components:

  • the CLI part, used to drive the instance but also used to initialize it.
  • the client part
  • the protocol
  • the server part
  • the TUI part

Implementation-wise, these 5 components are spread across only 3 Python modules:

  • moulti.cli (CLI + client)
  • moulti.protocol
  • (server + TUI)

The protocol does not neeed to work across network hosts, it simply needs to work across processes on a single host. At this stage, all IPC techniques remain available.

Enter another requirement: it should be possible to fill Moulti steps by piping the output of a command to the CLI, e.g.:

some_command --with arguments 2>&1 | moulti pass step_name

In a naive scenario, the CLI acts like a proxy: 1. the command writes to the pipe 2. the CLI reads from the pipe 3. the CLI writes to the instance 4. the instance reads from the CLI 5. the instance updates the step

A more straightforward approach is to pass the file descriptor the CLI would read from to the instance. This way: 1. the command writes to the pipe 2. the instance reads from the file descriptor 3. the instance updates the step

This can be achieved with Unix Domain Sockets (AF_UNIX) and SCM_RIGHTS ancillary data. Unix Domain Sockets are available on all Unix and Unix-like operating systems, and even on Windows. However, they bring security constraints: - on most platforms, Unix sockets are materialized by special files that appear on regular filesystems and file permissions determine what processes may or may not interact with the server. - in addition to this file-based mechanism, Linux also supports abstract sockets, the entry points of which no longer rely upon file permissions.

In almost all cases, the CLI and TUI components run as the exact same user and should never interact with any other user. However, it remains relevant to accept instructions from a whitelist of other users for specific use-cases.

With regular file-based Unix sockets, it is necessary to cautiously pick: - the permissions of the socket file; by default, they are derived from the user's umask, which cannot be predicted. - the directory that will host the socket file: - /tmp is very exposed and thus risky - /run/user/ is known to be protected and thus a perfect choice - directories under $HOME are typically (but not systematically) protected from other users and are therefore a suitable failover whenever /run/user is not available.

With abstract sockets, it is necessary to check the "credentials" of each incoming connection; here, "credentials" simply means "uid and gid". It is also possible to check those credentials with file-based Unix sockets but the mechanisms to do so suffer from portability issues.

Moulti: - defaults to abstract sockets with credentials check on Linux; - stores file-based Unix sockets in: - $XDG_RUNTIME_DIR (if this environment variable is set) - $XDG_CACHE_HOME/moulti (if this environment variable is set) - ~/Library/Caches/moulti (if ~/Library/Caches exists) - ~/.cache/moulti

Therefore, even with a particularly permissive umask value (e.g. umask 0), Moulti sockets should remain out of reach of other users.

Explicitly sharing a Moulti instance with other users remains possible:

  • Linux users simply need to stick with abstract sockets and set MOULTI_ALLOWED_UID and/or MOULTI_ALLOWED_GID.
  • Other users need to pick a suitable umask and a suitable path through MOULTI_SOCKET_PATH.

Additionally, operations feasible through the socket are essentially write-only. Consequently, a malicious user able to establish a connection with a Moulti instance that does not belong to them could:

  • send "ping" commands
  • change the title displayed by the instance
  • add new steps with arbitrary contents (possibly consuming large amounts of memory)
  • alter or erase existing steps, but only if they can guess their names
  • read answers to questions (this is the only command that may actually leak sensitive information)

... but they cannot:

  • list existing steps (bruteforce attacks remain possible though)
  • read properties of existing steps
  • read contents of existing steps
  • dump all current steps to disk (possibly filling the underlying storage)
  • copy any step to the clipboard
  • change appearance settings (TCSS, ANSI theme, dark/light mode)
  • execute any command

This last point is crucial: precisely because it listens on a network socket (even a strictly local one), Moulti does not provide any mechanism that could run a command passed through that socket. It does offer the ability to run a single command on startup but this command comes from command-line arguments passed to moulti run and thus from the rightful TUI owner.