Add system env variable expansion to envVars function

The function `envVars` has been updated to enable the application to also read system environment variables, in addition to CLI and env file variables. This change includes an update of the function's comment to reflect the new behavior, and the addition of new test cases to validate the feature. CLI variables override env file variables, which in turn override system environment variables if they share the same name.

cmd/spot/main.go

@@ -450,10 +450,16 @@ func setAdHocSSH(opts options, pbook *config.PlayBook) (*config.PlayBook, error)
 	return pbook, nil
 }
 
-// envVars returns a map of environment variables from the cli and env file, cli vars override env file vars if duplicated
+// envVars returns a map of environment variables from the cli, env file, and system env.
+// cli vars override env file vars, which in turn override system env vars if duplicated.
 func envVars(vars map[string]string, envFile string) (map[string]string, error) {
 	res := make(map[string]string)
 
+	expandEnv := func(value string) string {
+		// expand environment variables denoted by $var or ${var}
+		return os.Expand(value, os.Getenv)
+	}
+
 	// load env file vars
 	envFileData := struct {
 		Vars map[string]string `yaml:"vars"`
@@ -465,13 +471,13 @@ func envVars(vars map[string]string, envFile string) (map[string]string, error)
 			log.Printf("[WARN] can't parse env file %q: %v", envFile, err)
 		}
 		for k, v := range envFileData.Vars {
-			res[k] = v
+			res[k] = expandEnv(v)
 		}
 	}
 
 	// cli vars override env file vars
 	for k, v := range vars {
-		res[k] = v
+		res[k] = expandEnv(v)
 	}
 
 	return res, nil

cmd/spot/main_test.go

@@ -717,6 +717,9 @@ func Test_targetsForTask(t *testing.T) {
 }
 
 func TestEnvVars(t *testing.T) {
+	os.Setenv("ENV_VAR", "envValue")
+	defer os.Unsetenv("ENV_VAR")
+
 	tests := []struct {
 		name          string
 		cliVars       map[string]string
@@ -755,34 +758,53 @@ func TestEnvVars(t *testing.T) {
 			},
 			expectedError: false,
 		},
+		{
+			name: "system env var replacement",
+			cliVars: map[string]string{
+				"key1": "$ENV_VAR",
+				"key2": "${ENV_VAR}",
+				"key3": "${ENV_VAR_NOT_FOUND}",
+			},
+			envFileData: "",
+			expectedVars: map[string]string{
+				"key1": "envValue",
+				"key2": "envValue",
+				"key3": "",
+			},
+			expectedError: false,
+		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-
 			envFile := "/tmp/env-not-exist.yaml"
 			if tt.envFileData != "" {
-				// create a temp file
 				file, err := os.CreateTemp("", "*.yaml")
 				if err != nil {
 					t.Fatalf("could not create temp file: %v", err)
 				}
-				defer os.Remove(file.Name())
+				defer os.Remove(file.Name()) // Clean up
 
-				// write data to temp file
 				if _, err = file.WriteString(tt.envFileData); err != nil {
 					t.Fatalf("could not write to temp file: %v", err)
 				}
 
-				// close file
 				if err = file.Close(); err != nil {
 					t.Fatalf("could not close temp file: %v", err)
 				}
 				envFile = file.Name()
 			}
-			// get environment variables
+
 			actualVars, err := envVars(tt.cliVars, envFile)
-			assert.Equal(t, tt.expectedError, err != nil)
+			if err != nil && !tt.expectedError {
+				t.Errorf("envVars() error = %v, expectedError %v", err, tt.expectedError)
+				return
+			}
+			if err == nil && tt.expectedError {
+				t.Errorf("envVars() expected error, got none")
+				return
+			}
+
 			assert.Equal(t, tt.expectedVars, actualVars)
 		})
 	}