3 min read

Auto Activation

New in version 2.1

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

Bash

Add one line to your shell configuration file:

~/.bashrc
```
eval "$(devenv hook bash)"
```
Zsh

Add one line to your shell configuration file:

~/.zshrc
```
eval "$(devenv hook zsh)"
```
Fish

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:

~/.config/fish/config.fish
```
devenv hook fish | source
```
Nushell

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)
```

Passing arguments to `devenv shell`

New in version 2.3

Place arguments for the auto-activated devenv shell after --. For example, to disable the TUI in shells started by the Fish hook without changing other devenv commands:

~/.config/fish/config.fish

devenv hook fish -- --no-tui | source

The same separator works in every supported shell:

~/.bashrc

eval "$(devenv hook bash -- --no-tui)"

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.

Note

The hook detects projects by looking for a devenv.nix file. Before version 2.2, it looked for devenv.yaml instead, so projects with only devenv.nix were not auto-detected.

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.

Last updated Oct 11, 2026