工程师 - CVS版本管理工具

CVS - Concurrent Versions System

CVS 是一个版本控制系统，是源代码配置管理 (SCM) 的重要组成部分。使用它，你可以记录源文件和文档的历史。它的作用与自由软件 RCS、PRCS 和 Aegis 软件包类似。

CVS is a version control system, an important component of Source Configuration Management (SCM). Using it, you can record the history of sources files, and documents. It fills a similar role to the free software RCS, PRCS, and Aegis packages.

CVS 是一种生产质量控制系统，在全球广泛使用，包括许多自由软件项目。

CVS is a production quality system in wide use around the world, including many free software projects.

虽然 CVS 存储单个文件历史记录的格式与 RCS 相同，但与 RCS 相比，它具有以下显著优势：

* 它可以运行脚本，你可以提供脚本来记录 CVS 操作或执行特定站点的策略。

* 客户端/服务器 CVS 使分散在不同地域或慢速调制解调器上的开发人员能作为一个团队运作。版本历史记录存储在一台中央服务器上，客户端机器拥有开发人员正在处理的所有文件的副本。因此，客户端和服务器之间的网络必须正常运行才能执行 CVS 操作（如签入或更新），但不需要正常运行就能编辑或操作当前版本的文件。客户端可以执行与本地相同的所有操作。

* 由于地理位置和/或政策原因，多个开发人员或团队希望各自维护自己的文件版本，在这种情况下，CVS 的供应商分支可以从另一个团队（即使他们不使用 CVS）导入一个版本，然后 CVS 可以将供应商分支的更改与最新文件合并（如果需要的话）。

* 无保留签出，允许多个开发人员同时处理同一文件。

* CVS 提供了一个灵活的模块数据库，可将名称符号化地映射到更大的软件发行版中的组件。它将名称应用于目录和文件的集合。一条命令就能操作整个集合。

* CVS 服务器可在大多数 unix 变种上运行，也有 Windows NT/95、OS/2 和 VMS 客户端。在 Windows 95/NT 上，CVS 也可以在所谓的服务器模式下对本地存储库进行操作。

While CVS stores individual file history in the same format as RCS, it offers the following significant advantages over RCS:

* It can run scripts which you can supply to log CVS operations or enforce site-specific policies.

* Client/server CVS enables developers scattered by geography or slow modems to function as a single team. The version history is stored on a single central server and the client machines have a copy of all the files that the developers are working on. Therefore, the network between the client and the server must be up to perform CVS operations (such as checkins or updates) but need not be up to edit or manipulate the current versions of the files. Clients can perform all the same operations which are available locally.

* In cases where several developers or teams want to each maintain their own version of the files, because of geography and/or policy, CVS's vendor branches can import a version from another team (even if they don't use CVS), and then CVS can merge the changes from the vendor branch with the latest files if that is what is desired.

* Unreserved checkouts, allowing more than one developer to work on the same files at the same time.

* CVS provides a flexible modules database that provides a symbolic mapping of names to components of a larger software distribution. It applies names to collections of directories and files. A single command can manipulate the entire collection.

* CVS servers run on most unix variants, and clients for Windows NT/95, OS/2 and VMS are also available. CVS will also operate in what is sometimes called server mode against local repositories on Windows 95/NT.

CVS can be downloaded from  Index of /non-gnu/cvs.  

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CVS（并发版本系统）是最早用于软件开发的版本控制系统（VCS）之一。它帮助团队跟踪和管理源代码或其他文档随时间发生的变化，允许多个开发人员在一个项目上进行协作。下面将详细介绍 CVS 的工作原理和主要功能：

CVS (Concurrent Versions System) is one of the earliest version control systems (VCS) used in software development. It helps teams track and manage changes to the source code or other documents over time, allowing multiple developers to collaborate on a project. Here's a breakdown of how CVS works and its main features:

Key Concepts of CVS

1. 版本库和工作目录：

   - CVS 中的版本库存储了项目的完整历史，包括每个文件的所有版本。

   - 开发人员在名为工作目录的项目本地副本上工作，工作目录与版本库同步。本地所做的更改可以提交回版本库。

2. 版本管理：

   - CVS 跟踪文件或文件集的每个版本。开发人员每次进行修改时，新版本都会被保存下来，CVS 会记录所有修改，以便在需要时恢复到之前的版本。

   - 每个文件都有一个版本号，每次修改都会递增。

3. 并行开发：

   - CVS 允许多个开发人员同时开发同一个文件。开发人员将文件签出到本地工作区，并独立进行修改。

   - 当多人处理同一文件时，CVS 会在文件提交回版本库时合并他们的更改。如果出现相互冲突的更改，会通知开发人员手动解决。

4. 分支和标记

   - 分支：CVS 支持分支，允许开发人员创建平行的开发线。这对于开发实验性功能或项目的不同版本非常有用。

   - 标记： CVS 使用标签来标记代码库的特定状态，如发布版本。例如，在主要版本发布前，你可能会给所有文件打上 “v1.0 ”这样的标签。

5. 提交和更新：

   - 提交： 对工作目录中的文件进行修改后，开发人员可以将修改提交回版本库，创建文件的新版本。

   - 更新：开发人员可以更新本地工作目录，从版本库中调入最新更改。

1. Repository and Working Directory:

   - The repository in CVS stores the complete history of the project, including all versions of each file.

   - Developers work on a local copy of the project called the working directory, which is synchronized with the repository. Changes made locally can be committed back to the repository.

2. Versioning:

   - CVS tracks each version of a file or set of files. Every time a developer makes changes, the new version is saved, and CVS keeps a record of all the modifications, allowing you to revert to any previous version if needed.

   - Each file is assigned a version number, incremented with each change.

3. Concurrent Development:

   - CVS allows multiple developers to work on the same file concurrently. Developers check out files to their local workspace and make changes independently.

   - When multiple people work on the same file, CVS merges their changes when the files are committed back to the repository. If conflicting changes occur, the developers are notified to manually resolve them.

4. Branching and Tagging:

   - Branching: CVS supports branching, allowing developers to create parallel lines of development. This is useful for working on experimental features or different versions of a project.

   - Tagging: CVS uses tags to mark a specific state of the codebase, like a release version. For example, you might tag all the files with a label like `v1.0` before a major release.

5. Commit and Update:

   - Commit: After making changes to files in the working directory, a developer can commit the changes back to the repository, creating a new version of the files.

   - Update: Developers can update their local working directory to pull in the latest changes from the repository.

Main Features of CVS

1. 集中式版本控制：

   - CVS 采用集中模式，版本库托管在服务器上，开发人员通过检查文件的进出与版本库进行交互。所有更改都在单一版本库中进行跟踪。

2. 基于文本的系统：

   - CVS 主要用于处理文本文件，因此非常适合源代码管理，但对于图像或编译库等二进制文件则不太理想。

3. 历史和日志跟踪：

   - CVS 维护每个文件的修改历史，以及开发人员提交修改时的注释。这样，开发人员就可以查看修改历史、修改人和修改原因。

4. 简单合并：

   - CVS 允许自动合并不同开发人员对同一文件所做的修改，但在出现相互冲突的修改时可能需要人工干预。

5. 网络化操作：

   - CVS 是最早支持网络操作的版本控制系统之一，这意味着开发人员可以通过网络与远程版本库交互，在不同地点工作。

1. Centralized Version Control:

   - CVS follows a centralized model where the repository is hosted on a server, and developers interact with it by checking files in and out. All changes are tracked in a single repository.

2. Text-Based System:

   - CVS was primarily designed for handling text files, making it well-suited for source code management but not ideal for binary files like images or compiled libraries.

3. History and Log Tracking:

   - CVS maintains a history of changes for every file, along with comments from developers when they commit changes. This allows developers to review the history of changes, who made them, and why.

4. Simple Merging:

   - CVS allows automatic merging of changes made by different developers to the same file, though it may require manual intervention in the case of conflicting changes.

5. Networked Operation:

   - CVS was one of the first version control systems to support networked operation, meaning developers could work from different locations by interacting with a remote repository over the network.

Limitations of CVS

1. 无原子提交：

   - 在 CVS 中，提交是基于文件的，而不是基于事务的。这意味着如果在提交过程中出现问题，可能只会保存部分更改，从而导致版本库中出现不一致的状态。

2. 对二进制文件的支持较弱：

   - CVS 在设计上无法有效处理二进制文件。二进制文件的存储和版本控制会导致效率低下和版本库增大。

3. 分支和合并难题：

   - 虽然 CVS 支持分支，但与现代系统相比，管理分支并将其合并回开发主线的过程更为复杂且容易出错。

4. 性能问题：

   - 随着项目规模的扩大，CVS 会变得缓慢且难以管理，尤其是对于大型团队或大型代码库而言。

1. No Atomic Commits:

   - In CVS, commits are file-based, not transaction-based. This means if something goes wrong during a commit, only part of the changes may be saved, leading to inconsistent states in the repository.

2. Weak Support for Binary Files:

   - CVS was not designed to handle binary files effectively. Storing and versioning binary files can lead to inefficiencies and larger repositories.

3. Branching and Merging Challenges:

   - While CVS supports branching, the process of managing branches and merging them back into the main line of development is more complex and error-prone compared to modern systems.

4. Performance Issues:

   - As projects grow larger, CVS can become slow and difficult to manage, especially for large teams or large codebases.

Why CVS Became Obsolete

CVS 在当时是一个重要的工具，但现在基本上已被 Subversion (SVN)、Git 和 Mercurial 等更先进的版本控制系统所取代。这些较新的系统解决了 CVS 的许多局限性，如更好地处理分支、原子提交，以及提高大型项目的性能。

CVS was an important tool in its time, but it has largely been replaced by more advanced version control systems like Subversion (SVN), Git, and Mercurial. These newer systems address many of the limitations of CVS, such as better handling of branches, atomic commits, and improved performance for larger projects.

总之，CVS 是一种集中式版本控制系统，它帮助形成了现代软件开发实践，但由于其局限性，它已被更强大、更灵活的工具所取代。

In summary, CVS is a centralized version control system that helped shape modern software development practices, but due to its limitations, it has been replaced by more powerful and flexible tools.

参考；

CVS - Open Source Version Control (nongnu.org)