add ability to load from .env files before invoking the command

Cargo.toml

@@ -92,6 +92,7 @@ directories = { version = "5.0.1" }
 dirs-sys = { version = "0.4.1" }
 dunce = { version = "1.0.5" }
 either = { version = "1.13.0" }
+dotenvy = { version = "0.15.7" }
 encoding_rs_io = { version = "0.1.7" }
 etcetera = { version = "0.8.0" }
 flate2 = { version = "1.0.33", default-features = false }

crates/uv-cli/src/lib.rs

@@ -2660,6 +2660,12 @@ pub struct RunArgs {
     /// By default, environment modifications are omitted, but enabled under `--verbose`.
     #[arg(long, env = "UV_SHOW_RESOLUTION", value_parser = clap::builder::BoolishValueParser::new(), hide = true)]
     pub show_resolution: bool,
+
+    /// Run the command and load environment variables from the `.env` file in the current project.
+    ///
+    /// By default, the .env file is not loaded.
+    #[arg(long, env = "UV_RUN_LOAD_DOTENV")]
+    pub load_dotenv: bool,
 }
 
 #[derive(Args)]

crates/uv/Cargo.toml

@@ -59,6 +59,7 @@ axoupdater = { workspace = true, features = [
 ], optional = true }
 clap = { workspace = true, features = ["derive", "string", "wrap_help"] }
 ctrlc = { workspace = true }
+dotenvy = { workspace = true }
 flate2 = { workspace = true, default-features = false }
 fs-err = { workspace = true, features = ["tokio"] }
 futures = { workspace = true }

crates/uv/src/commands/project/run.rs

@@ -47,6 +47,7 @@ use crate::commands::reporters::PythonDownloadReporter;
 use crate::commands::{diagnostics, project, ExitStatus, SharedState};
 use crate::printer::Printer;
 use crate::settings::ResolverInstallerSettings;
+use dotenvy::dotenv_override;
 
 /// Run a command.
 #[allow(clippy::fn_params_excessive_bools)]
@@ -68,6 +69,7 @@ pub(crate) async fn run(
     editable: EditableMode,
     python: Option<String>,
     settings: ResolverInstallerSettings,
+    load_dotenv: bool,
     python_preference: PythonPreference,
     python_downloads: PythonDownloads,
     connectivity: Connectivity,
@@ -823,6 +825,14 @@ pub(crate) async fn run(
     debug!("Running `{command}`");
     let mut process = command.as_command(interpreter);
 
+    // Load the `.env` into the environment if the flag or ENV is set.
+    // This is done before setting the PATH or VIRTUAL_ENV environment variables
+    // to ensure they are not overwritten
+    if load_dotenv {
+        debug!("Loading `.env` file");
+        dotenv_override().ok();
+    };
+
     // Construct the `PATH` environment variable.
     let new_path = std::env::join_paths(
         ephemeral_env

crates/uv/src/lib.rs

@@ -1257,6 +1257,7 @@ async fn run_project(
                 args.editable,
                 args.python,
                 args.settings,
+                args.load_dotenv,
                 globals.python_preference,
                 globals.python_downloads,
                 globals.connectivity,

crates/uv/src/settings.rs

@@ -236,6 +236,7 @@ pub(crate) struct RunSettings {
     pub(crate) python: Option<String>,
     pub(crate) refresh: Refresh,
     pub(crate) settings: ResolverInstallerSettings,
+    pub(crate) load_dotenv: bool,
 }
 
 impl RunSettings {
@@ -267,6 +268,7 @@ impl RunSettings {
             no_project,
             python,
             show_resolution,
+            load_dotenv,
         } = args;
 
         Self {
@@ -295,6 +297,7 @@ impl RunSettings {
                 resolver_installer_options(installer, build),
                 filesystem,
             ),
+            load_dotenv,
         }
     }
 }

docs/configuration/environment.md

@@ -75,6 +75,9 @@ uv accepts the following command-line arguments as environment variables:
   set, uv will use this password for publishing.
 - `UV_NO_SYNC`: Equivalent to the `--no-sync` command-line argument. If set, uv will skip updating
   the environment.
+- `UV_RUN_LOAD_DOTENV`: Equivalent to the `--load-dotenv` command-line argument. If set, `uv run`
+  will load the .env file from the current project directory (if it exists) to load all ENVs into
+  the current process.
 
 In each case, the corresponding command-line argument takes precedence over an environment variable.
 

docs/reference/cli.md

@@ -214,6 +214,11 @@ uv run [OPTIONS] [COMMAND]
 
 <li><code>symlink</code>:  Symbolically link packages from the wheel into the <code>site-packages</code> directory</li>
 </ul>
+</dd><dt><code>--load-dotenv</code></dt><dd><p>Run the command and load environment variables from the <code>.env</code> file in the current project.</p>
+
+<p>By default, the .env file is not loaded.</p>
+
+<p>May also be set with the <code>UV_RUN_LOAD_DOTENV</code> environment variable.</p>
 </dd><dt><code>--locked</code></dt><dd><p>Assert that the <code>uv.lock</code> will remain unchanged.</p>
 
 <p>Requires that the lockfile is up-to-date. If the lockfile is missing or needs to be updated, uv will exit with an error.</p>