fix: print friendly error for missing command in dotenv run (#606)

Changes for users:

- (BREAKING) `dotenv run` exits with status code 1 instead of 2 if the command
  provided as argument can't be found.
- `dotenv run` prints a friendly error message instead of a stack trace
  if the command provided as argument can't be found.

Notes:

The existing test case was wrongly testing for that situation: it was
actually observing a "missing env file" error, not a "command not found
error". I thus added an appropriate test case for full coverage.

Co-authored-by: Saurabh Kumar <theskumar@users.noreply.github.com>

Author: bbc2

src/dotenv/cli.py

@@ -228,9 +228,20 @@ def run_command(command: List[str], env: Dict[str, str]) -> None:
     if sys.platform == "win32":
         # execvpe on Windows returns control immediately
         # rather than once the command has finished.
-        p = Popen(command, universal_newlines=True, bufsize=0, shell=False, env=cmd_env)
+        try:
+            p = Popen(
+                command, universal_newlines=True, bufsize=0, shell=False, env=cmd_env
+            )
+        except FileNotFoundError:
+            print(f"Command not found: {command[0]}", file=sys.stderr)
+            sys.exit(1)
+
         _, _ = p.communicate()
 
         sys.exit(p.returncode)
     else:
-        os.execvpe(command[0], args=command, env=cmd_env)
+        try:
+            os.execvpe(command[0], args=command, env=cmd_env)
+        except FileNotFoundError:
+            print(f"Command not found: {command[0]}", file=sys.stderr)
+            sys.exit(1)

tests/test_cli.py

@@ -237,7 +237,21 @@ def test_run_without_cmd(tmp_path):
     assert "Invalid value for '-f'" in result.stderr
 
 
-def test_run_with_invalid_cmd(tmp_path):
+def test_run_with_invalid_cmd(dotenv_path, tmp_path):
+    result = run_dotenv(
+        ["--file", str(dotenv_path), "run", "i_do_not_exist"],
+        cwd=tmp_path,
+    )
+
+    check_process(result, exit_code=1)
+    assert "Command not found: i_do_not_exist" in result.stderr
+
+
+def test_run_with_env_missing_and_invalid_cmd(tmp_path):
+    """
+    Check that an .env file missing takes precedence over a command not found error.
+    """
+
     result = run_dotenv(["run", "i_do_not_exist"], cwd=tmp_path)
 
     check_process(result, exit_code=2)