Sanitize project name when using directory name

Sources/Container-Compose/Commands/ComposeDown.swift

@@ -86,7 +86,7 @@ public struct ComposeDown: AsyncParsableCommand {
                 "Note: The 'name' field currently only affects container naming (e.g., '\(name)-serviceName'). Full project-level isolation for other resources (networks, implicit volumes) is not implemented by this tool."
             )
         } else {
-            projectName = URL(fileURLWithPath: cwd).lastPathComponent  // Default to directory name
+            projectName = deriveProjectName(cwd: cwd)
             print("Info: No 'name' field found in docker-compose.yml. Using directory name as project name: \(projectName ?? "")")
         }
 

Sources/Container-Compose/Commands/ComposeUp.swift

@@ -119,7 +119,7 @@ public struct ComposeUp: AsyncParsableCommand, @unchecked Sendable {
                 "Note: The 'name' field currently only affects container naming (e.g., '\(name)-serviceName'). Full project-level isolation for other resources (networks, implicit volumes) is not implemented by this tool."
             )
         } else {
-            projectName = URL(fileURLWithPath: cwd).lastPathComponent  // Default to directory name
+            projectName = deriveProjectName(cwd: cwd)
             print("Info: No 'name' field found in docker-compose.yml. Using directory name as project name: \(projectName ?? "")")
         }
 

Sources/Container-Compose/Helper Functions.swift

@@ -93,6 +93,17 @@ public func resolveVariable(_ value: String, with envVars: [String: String]) ->
     return resolvedValue
 }
 
+/// Derives a project name from the current working directory. It replaces any '.' characters with
+/// '_' to ensure compatibility with container naming conventions.
+///
+/// - Parameter cwd: The current working directory path.
+/// - Returns: A sanitized project name suitable for container naming.
+public func deriveProjectName(cwd: String) -> String {
+    // We need to replace '.' with _ because it is not supported in the container name
+    let projectName = URL(fileURLWithPath: cwd).lastPathComponent.replacingOccurrences(of: ".", with: "_")
+    return projectName
+}
+
 extension String: @retroactive Error {}
 
 /// A structure representing the result of a command-line process execution.

Tests/Container-Compose-StaticTests/HelperFunctionsTests.swift

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Morris Richman and the Container-Compose project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import Testing
+import Foundation
+@testable import ContainerComposeCore
+
+@Suite("Helper Functions Tests")
+struct HelperFunctionsTests {
+
+    @Test("Derive project name from current working directory - contains dot")
+    func testDeriveProjectName() throws {
+        var cwd = "/Users/user/Projects/My.Project"
+        var projectName = deriveProjectName(cwd: cwd)
+        #expect(projectName == "My_Project")
+
+        cwd = ".devcontainers"
+        projectName = deriveProjectName(cwd: cwd)
+        #expect(projectName == "_devcontainers")
+    }
+
+}