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

Cargo.toml

@@ -83,6 +83,7 @@ data-encoding = { version = "2.5.0" }
 directories = { version = "5.0.1" }
 dirs-sys = { version = "0.4.1" }
 dunce = { version = "1.0.4" }
+dotenv = { version = "0.15.0" }
 either = { version = "1.12.0" }
 encoding_rs_io = { version = "0.1.7" }
 etcetera = { version = "0.8.0" }

crates/uv-cli/src/lib.rs

@@ -2509,6 +2509,12 @@ 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

@@ -81,6 +81,7 @@ unicode-width = { workspace = true }
 url = { workspace = true }
 which = { workspace = true }
 zip = { workspace = true }
+dotenv = { workspace = true }
 
 [target.'cfg(target_os = "windows")'.dependencies]
 mimalloc = { version = "0.1.39" }

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

@@ -41,6 +41,7 @@ use crate::commands::reporters::PythonDownloadReporter;
 use crate::commands::{project, ExitStatus, SharedState};
 use crate::printer::Printer;
 use crate::settings::ResolverInstallerSettings;
+use dotenv::dotenv;
 
 /// Run a command.
 #[allow(clippy::fn_params_excessive_bools)]
@@ -60,6 +61,7 @@ pub(crate) async fn run(
     dev: bool,
     python: Option<String>,
     settings: ResolverInstallerSettings,
+    load_dotenv: bool,
     python_preference: PythonPreference,
     python_downloads: PythonDownloads,
     connectivity: Connectivity,
@@ -686,6 +688,11 @@ pub(crate) async fn run(
     debug!("Running `{command}`");
     let mut process = command.as_command(interpreter);
 
+    // Load the `.env` if necessary.
+    if load_dotenv {
+        dotenv().ok();
+    };
+
     // Construct the `PATH` environment variable.
     let new_path = std::env::join_paths(
         ephemeral_env

crates/uv/src/lib.rs

@@ -1136,6 +1136,7 @@ async fn run_project(
                 args.dev,
                 args.python,
                 args.settings,
+                args.load_dotenv,
                 globals.python_preference,
                 globals.python_downloads,
                 globals.connectivity,

crates/uv/src/settings.rs

@@ -221,6 +221,7 @@ pub(crate) struct RunSettings {
     pub(crate) python: Option<String>,
     pub(crate) refresh: Refresh,
     pub(crate) settings: ResolverInstallerSettings,
+    pub(crate) load_dotenv: bool,
 }
 
 impl RunSettings {
@@ -248,6 +249,7 @@ impl RunSettings {
             no_project,
             python,
             show_resolution,
+            load_dotenv,
         } = args;
 
         Self {
@@ -275,6 +277,7 @@ impl RunSettings {
                 resolver_installer_options(installer, build),
                 filesystem,
             ),
+            load_dotenv,
         }
     }
 }

docs/configuration/environment.md

@@ -63,6 +63,9 @@ uv accepts the following command-line arguments as environment variables:
   `--no-python-downloads` option. Whether uv should allow Python downloads.
 - `UV_COMPILE_BYTECODE`: Equivalent to the `--compile-bytecode` command-line argument. If set, uv
   will compile Python source files to bytecode after installation.
+- `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.