direnv

Direnv is an environment management tool that automatically loads and unloads environment variables based on the current working directory. It works by pairing a shell extension with per-directory configuration files named .envrc, allowing projects to specify their runtime environment independent of the global shell state.

Operation and workflow: Direnv installs a shell hook that runs whenever you change directories. If the target directory contains an .envrc, direnv evaluates the file and exports or unexports environment variables in your current shell. To prevent unintended execution of arbitrary commands, direnv requires explicit user approval via the direnv allow command before an .envrc becomes active. When you leave the directory or move to one without an .envrc, the previously set variables are automatically removed or reset.

Usage and examples: In a project root, you can create an .envrc that exports variables or adjusts PATH, such as exporting VAR=value or extending PATH. Direnv also provides a layout directive to integrate with language-specific environments, for example layout python to activate a Python virtual environment. Commands inside .envrc are executed in a controlled fashion, and only after you authorize them with direnv allow.

Security and considerations: A key security aspect is that .envrc files can run arbitrary shell commands. Therefore, users should review an .envrc before granting approval. Direnv supports trust-management practices, including marking directories as trusted to streamline subsequent activations, and it can be configured to be more conservative in its activation behavior.

Availability and compatibility: Direnv provides shell integrations for Bash, Zsh, Fish, Tcsh, and other POSIX-compatible shells. It is designed to work on Unix-like systems such as Linux and macOS, with usage on Windows typically via compatible environments that run POSIX shells.