feat: allow variable escaping in manifest

internal/pkg/manifest/interpolate.go

@@ -23,7 +23,7 @@ var (
 	// Taken from docker/compose.
 	// Environment variable names consist solely of uppercase letters, digits, and underscore,
 	// and do not begin with a digit. （https://pubs.opengroup.org/onlinepubs/007904875/basedefs/xbd_chap08.html）
-	interpolatorEnvVarRegExp = regexp.MustCompile(`\${([_a-zA-Z][_a-zA-Z0-9]*)}`)
+	interpolatorEnvVarRegExp = regexp.MustCompile(`(\\?)\${([_a-zA-Z][_a-zA-Z0-9]*)}`)
 )
 
 // Interpolator substitutes variables in a manifest.
@@ -106,7 +106,14 @@ func (i *Interpolator) interpolatePart(s string) (string, error) {
 	replaced := s
 	for _, match := range matches {
 		// https://pkg.go.dev/regexp#Regexp.FindAllStringSubmatch
-		key := match[1]
+		key := match[2]
+
+		if match[1] == "\\" {
+			// variable is escaped (e.g. \${foo}) -> no substitution is desired, let's just remove the leading backslash
+			replaced = strings.ReplaceAll(replaced, fmt.Sprintf("\\${%s}", key), fmt.Sprintf("${%s}", key))
+			continue
+		}
+
 		currSegment := fmt.Sprintf("${%s}", key)
 		predefinedVal, isPredefined := i.predefinedEnvVars[key]
 		osVal, isEnvVarSet := os.LookupEnv(key)

internal/pkg/manifest/interpolate_test.go

@@ -117,6 +117,23 @@ network:
       - sg-3
 `,
 		},
+		"should not substitute escaped dollar signs": {
+			inputStr: "echo \\${name}",
+			inputEnvVar: map[string]string{
+				"name": "this variable should not be read",
+			},
+			wanted: "echo ${name}\n",
+		},
+		"should substitute variables right after one another": {
+			inputStr: "${a}${b}\\${c}${d}",
+			inputEnvVar: map[string]string{
+				"a": "A",
+				"b": "B",
+				"c": "C",
+				"d": "D",
+			},
+			wanted: "AB${c}D\n",
+		},
 	}
 
 	for name, tc := range testCases {

site/content/docs/developing/manifest-env-var.en.md

@@ -53,3 +53,15 @@ Copilot will substitute `${COPILOT_APPLICATION_NAME}` and `${COPILOT_ENVIRONMENT
 $ copilot svc deploy --app my-app --env test
 ```
 to deploy the service to the `test` environment in your `my-app` application, Copilot will resolve `/copilot/${COPILOT_APPLICATION_NAME}/${COPILOT_ENVIRONMENT_NAME}/secrets/db_password` to `/copilot/my-app/test/secrets/db_password`. (For more information of secret injection, see [here](../developing/secrets.en.md)).
+
+## Escaping
+If variable substitution is undesired, add a leading backslash:
+
+```yaml
+command: echo hello \${name}
+# or command: "echo \\${name}"
+variable:
+  name: world
+```
+
+In this case Copilot will not attempt to substitute `${name}` with the value of the environment variable `name`.