Auto Activation

devenv includes a built in shell hook that automatically activates your developer environment when you cd into a project directory. No external tools required.

Setup

Add one line to your shell configuration file:

eval "$(devenv hook bash)"

Add one line to your shell configuration file:

eval "$(devenv hook zsh)"

Usually nothing to do — devenv installed via Nix ships a snippet that fish loads automatically. If it doesn’t load for you, add this instead:

devenv hook fish | source

Usually nothing to do — devenv installed via Nix ships a snippet that nu loads automatically. If it doesn’t load for you, add this instead:

Run once, in Nu:

mkdir ($nu.default-config-dir | path join autoload)
devenv hook nu | save --force ($nu.default-config-dir | path join autoload/devenv-hook.nu)

Trusting a project

Before a project can auto activate, you need to explicitly trust it. This is a security measure that prevents untrusted projects from modifying your shell.

Navigate to the project directory and run:

$ cd ~/myproject
$ devenv allow
devenv: allowed /home/user/myproject

To activate one or more profiles whenever the project is entered, pass them when allowing it:

$ devenv --profile backend --profile observability allow
devenv: allowed /home/user/myproject with profile backend, observability

The selected profiles also apply to subsequent devenv commands in the project. An explicit --profile takes priority. Run plain devenv allow again to clear the saved profile selection without revoking trust.

When you cd into the directory next time, devenv will automatically start a shell:

$ cd ~/myproject
(devenv) $

Revoking trust

To stop a project from auto activating:

$ cd ~/myproject
$ devenv revoke
devenv: revoked /home/user/myproject

How it works

The hook runs on every directory change and:

Checks the trust database to verify the project was allowed.
If trusted, runs devenv shell in a subshell for that project.

If a project has not been trusted yet, you will see a message asking you to run devenv allow:

devenv: /home/user/myproject is not allowed. Run 'devenv allow' to trust this directory.

Automatic deactivation

When you cd out of the project directory (or any of its subdirectories), the devenv shell exits automatically and you return to your normal shell:

(devenv) $ cd ..
$

Re-entry protection

The hook will not nest environments. While inside a devenv shell, navigating into a subdirectory of the same project keeps the current shell. Only navigating outside the project triggers deactivation.

Comparison with direnv

Feature	`devenv hook`	direnv
External dependencies	None	Requires direnv
Setup	One line in shell config	direnv install + `.envrc` per project
Trust granularity	Per project directory	Per `.envrc` file
Environment application	Spawns a subshell	Modifies current shell in place
Unloading on exit	Subshell exits automatically	direnv unloads variables

Use devenv hook for a simple, dependency free setup. Use direnv if you prefer in place environment modification without a subshell.