Traditionally, the way to set the values of environment variables in Houdini was to edit the houdini.env file. The most important variable to set up is the $HOUDINI_PATH, which tells Houdini where to look for files such as assets. You can also create convenience variables (for example $TEXTURE_DIR) and edit system variables (such as the binary search path $PATH).

The problem is that not only the user wants to set environment variables, but also studios, plug-in authors, and so on. Multiple parties would end up rewriting or appending to the houdini.env file, sometimes causing errors or redundancy.

Also, you might want variables defined some times and not others (for example, switching between project-specific paths, or turning “experimental” assets on and off).

The new solution for this kind of set-up is packages. Packages are .json files in HOUDINI_PATH/packages. Each package file contains a specification for how to modify the environment (including the Houdini Path and other variables).

You can then have separate packages for:

• Studio variables.

• Project variables.

• User variables.

• Variables for each separate plug-in, tool, or add-on.

The file format supports a small expression language to allow some automation. With expressions you can, for example:

• Enable/disable a tool installation or specify what package(s) are required by a tool.

• Write generic package files.

• Write a single package to manage a multi-platform setup.

• Set variables conditionally with simple operators, Houdini keywords and environment variables.

This removes the need to edit houdini.env.

• Package files must be valid JSON and must have the .json extension.

• Houdini will scan the following directories on startup (if they exist) for package files:

  • $HOUDINI_USER_PREF_DIR/packages

  • $HSITE/houdinimajor.minor/packages (for example, $HSITE/houdini18.0/packages)

  • $HOUDINI_PACKAGE_DIR

    Houdini will process the package files directly in the folders specified in HOUDINI_PACKAGE_DIR, do not add a packages directory under these folders.

    $HSITE must be set to an existing directory before starting Houdini.

  • $HFS/packages

• Houdini process files it finds first in the directory order above, then within each directory alphabetically by file name. The processing order can be changed with the process_order keyword.

• You can have multiple package files in each packages directory on the above path.

• Houdini does not scan subdirectories inside packages.

• Extra package folders can be specified dynamically from a package file.

The following keywords are used for writing a package:

env

Sets or modifies environment variables.

enable

Enables or disables a package.

load_package_once

Prevents a package from being loaded multiple times. Houdini will load the first package in the search path with "load_package_once": true, and ignore any other packages with the same file name in the search path. This keyword defaults to false.

process_order

Specifies an integer value that Houdini can use for arranging the order of the packages to process in a package directory.

package_path

Scans package paths dynamically.

path

Shortcut to set HOUDINI_PATH.

recommends

Checks specific package(s) availability without enforcing a dependency.

requires

Checks specific package(s) availability and enforces a dependency.

https://andcgi.medium.com/houdini-packages-multiple-render-engines-environment-variable-c517df426440