pixi exec

Run a command in a temporary environment

Runs a command in a temporary environment, installing the required packages on-the-fly. This is useful for running tools without permanently installing them.

The temporary environments are cached and can be removed with pixi clean cache --exec.

Usage

pixi exec [OPTIONS] <COMMAND>...

Alias: pixi x

Arguments

COMMAND · string · required

The executable to run, followed by any arguments.

If no package specs are provided with --spec, pixi will attempt to guess the package name from the command.

Options

--spec · string

Matchspecs of packages to install.

If this is not provided, the package is guessed from the command name.

Can be specified multiple times.

--with · string

Matchspecs of packages to install, while also guessing a package from the command.

This option allows you to specify additional dependencies alongside the auto-guessed package.

Cannot be used together with --spec.

--channel · string

The channels to consider as a name or a URL. Multiple channels can be specified by using this field multiple times.

When specifying a channel, it is common that the selected channel also depends on the conda-forge channel.

By default, if no channel is provided, conda-forge is used.

--platform · string

The platform to create the environment for. Defaults to the current platform.

--force-reinstall · boolean

If specified, a new environment is always created even if one already exists.

--list · string

Before executing the command, list packages in the environment.

Specify --list=some_regex to filter the shown packages.

--no-modify-ps1 · boolean

Disable modification of the PS1 prompt to indicate the temporary environment.

Examples

Run a command with auto-guessed package

pixi exec python --version

This will install Python in a temporary environment and run python --version.

Run a command with specific package versions

pixi exec --spec python==3.12 python script.py

Run a command with multiple packages

pixi exec --spec jupyter --spec polars jupyter lab

Run with additional dependencies

pixi exec --with polars jupyter lab

This installs both jupyter (guessed from the command) and polars (specified with --with).

Use a specific channel

pixi exec --channel conda-forge --channel bioconda samtools --version

Force reinstall

pixi exec --force-reinstall python script.py

List packages before execution

pixi exec --list python --version

List only specific packages:

pixi exec --list="numpy.*" python script.py

Cross-platform execution

# On macOS ARM, run a tool for x86_64
pixi exec --platform osx-64 some-tool

How It Works

1. Package Resolution: If --spec is not provided, pixi guesses the package name from the command
2. Environment Creation: Pixi creates (or reuses) a cached environment with the required packages
3. Execution: The command runs in the activated environment
4. Caching: The environment is cached for future use

Temporary environments are stored in the pixi cache directory and are reused across invocations with the same dependencies.

Environment Naming

Temporary environments are named based on:

• The command name
• The package specifications
• The channels used
• The target platform

The same environment is reused for identical combinations.

Cleaning Up

Remove all temporary exec environments:

pixi clean cache --exec

Use Cases

One-off Commands

# Run a tool without installing it globally
pixi exec cowpy "Hello World"

Testing Different Versions

pixi exec --spec python==3.8 python --version
pixi exec --spec python==3.12 python --version

Quick Scripts

pixi exec --spec "python==3.12" --with "requests" python -c "import requests; print(requests.get('https://api.github.com').json())"

CI/CD

# In GitHub Actions
- name: Run tool
  run: pixi exec cowpy "Build successful!"

Package Guessing

When you don’t specify --spec, pixi attempts to guess the package name:

pixi exec python --version  # Guesses package name: python
pixi exec jupyter lab       # Guesses package name: jupyter

Illegal characters in the command are replaced with dashes.

Use pixi x as a shorthand for pixi exec.

Differences from pixi run

Feature	pixi exec	pixi run
Scope	Temporary environment	Project environment
Package source	Specified via CLI	From pixi.toml
Caching	Automatic	N/A
Use case	One-off commands	Project tasks

Environment Variables

The temporary environment sets:

• PIXI_ENVIRONMENT_NAME: temp:<package-names>
• PS1 or _PIXI_PROMPT: Modified prompt (unless --no-modify-ps1)
• All standard conda environment variables