Sccs file history

It is written in C and was designed to be a more robust centralized solution than CVS. Like CVS, Subversion uses a centralized repository model. Remote users must have a working network connection to commit their changes to the central repository. Subversion introduced the functionality of atomic commits which ensured that a commit would either fully succeed, or be completely abandoned if an issue occurred. In CVS, if a commit operation failed midway, for example due to a network outage, the repository could be left in a corrupted and inconsistent state.

Furthermore, a commit or revision in Subversion can include multiple files and directories. This is important since it allows users to track sets of related changes together as a grouped unit, instead of the past storage models that track changes separately for each file.

This name was chosen since it creates its database structure using a file and directory structure that match the operating system filesystem it is running on. The unique feature of the Subversion filesystem is that it is designed to track not only the files and the directories it contains, but the different versions of these files and directories and they change over time.

It is a filesystem with an added time dimension. In addition, folders are first class citizens in Subversion. Empty folders can be committed in Subversion, whereas in the rest even Git empty folders are unnoticed. When a Subversion repository is created, a nearly empty database of files and folders is created as a part of it. Each commit which can include changes to multiple files is stored in a new file in the revs directory and is named with a sequential numeric identifier starting with 1.

When a file is committed for the first time, its full content is stored. Future commits of the same file will store only the changes - also called the diffs or deltas - in order to conserve space.

In addition, the deltas are compressed using lz4 or zlib compression algorithms to further reduce their size. By default, this is actually only true to a point.

Although storing file deltas instead of the whole file each time does save on storage space, it adds time to checkout and commit operations since all the deltas need to be strung together in order to recreate the current state of the file.

For this reason, by default Subversion stores up to deltas per file before storing a new full copy of the file. This achieves a nice balance of both storage and speed. SVN does not use a conventional branching and tagging system. A normal Subversion repository layout is to have three folders in the root:. The message of the initial commit is typically set to 'Initial commit'.

This will checkout the specified branch. Note this needs to be committed afterwards. Git was created in by Linus Torvalds also the creator of Linux and is written primarily in C combined with some shell scripts. It is a great VCS due to its features, flexibility, and speed. Linus Torvalds originally wrote it for the Linux codebase and it has grown to become the most popular VCS in use today.

Git repositories are commonly hosted on local servers as well as cloud services. Git is a distributed VCS. This means that no copy of the repository needs to be designated as the centralized copy - all copies are created equal. This is in stark contrast to the second generation VCS which rely on a centralized copy for users to checkin and checkout from.

What this means is that developers can share changes with each other directly before merging their changes into an official branch. Furthermore, developers can commit their changes to their local copy of the repository without any other repositories knowing about it.

This means that commits can be made without any network or Internet connection. Developers can work locally offline until they are ready to share their work with others. At that point, the changes can be pushed to other repositories for review, testing, or deployment. When a file is added for tracking with Git, it is compressed using the zlib compression algorithm. The result is hashed using a SHA-1 hash function.

This yields a unique hash value that corresponds specifically to the content in that file. Git stores this in an object database which is located in the hidden. The name of the file is the generated hash value, and the file contains the compressed content. These files are called blobs and are created each time a new file or changed version of an existing file are added to the repository. Git implements a staging index which acts as an intermediate area for changes that are getting ready to be committed.

As new changes are staged for commit, their compressed contents are referenced in a special index file - which takes the form of a tree object. A tree is a Git object that connects blob objects to their real file names, file permissions and links to other trees, and in this way represents the state of a particular set of files and directories. Once all related changes are staged for commit, the index tree can be committed to the repository, which creates a commit object in the Git object database.

A commit references the head tree for a particular revision as well as the commit author, email address, date, and a descriptive commit message. Each commit also stores a reference to its parent commit s and so over time a history of project development is established. As mentioned, all Git objects - blobs, trees, and commits - are compressed, hashed, and stored in the object database based on their hash value.

These are called loose objects. At this point no diffs have been utilized to save space which makes Git very fast since the full content of each file revision is accessible as a loose object.

However, certain operations such as pushing commits to a remote repository, storing too many objects, or manually running Git's garbage collection command can cause Git to repackage the objects into pack files.

In the packing process, reverse diffs are taken and compressed to eliminate redundant content and reduce size. This process results in. These pack files are transferred over the network when branches are pushed to or pulled from remote repositories.

When pulling or fetching branches, the pack files are unpacked to create the loose objects in the object repository. I read this book a few years ago and it clarified a lot of Git concepts and commands that I now use almost every day! SCCS lets you put files under configuration control, check out read-only copies, acquire write locks for updates, check in and document changes, print histories, and identify and combine specific updates.

Any text file can be put under SCCS's control, making it useful for managing plain text documentation and meeting notes.

To change the file, you check it out for editing, and then each subsequent change to the file is annotated in the history file when you check the modified version back in.

SCCS locks the history file while one user is editing it to prevent concurrent updates. Let's walk through some basic SCCS operations to see how the components fit together, and then get into the grittier problems that make SCCS more of a benefit than an added burden.

We'll use the front-end for illustrative purposes, but you can also call the SCCS subcommands directly. Make sure you have an obvious place to store history files, such as a subdirectory called SCCS. SCCS commands look for this subdirectory if you don't give an explicit history file location. You want the history file and the actual file to be namesakes unless you're particularly good at associating strange path names with your. You can choose any file you want for the initialization; if you've just sorted your hosts file into.

The most common complaint is that the initial file doesn't contain any ID keywords, which are magic strings filled in by SCCS with the file name, delta numbers, and date and time stamps. We'll talk about the keywords and how to maximize your enjoyment of them shortly. All revisions, delta histories and access control information goes into the s-file. After you initialize a history file, be sure to rename or remove the initial file to prevent problems on your first check-out operation.

This time, we're told the new delta number to be created by our editing session. If someone else is editing the file at the time, SCCS produces an error:. Our first contention point is removed: any request to edit a file that is already being consumed by another system administrator is met with a cryptic yet gentle slap on the keyboard. How can you determine the version number of a file, or if it's even SCCS controlled?

Unreadable s. Force encoding of binary data. The contents of such files are stored in the history file in encoded form.

See uuencode 1C for details about the encoding. This option is normally used in conjunction with -i to force admin to encode initial versions not recognized as containing binary data.

Check the structure of an existing s. Recompute the file check-sum and store it in the first line of the s. Caution: it is important to verify the contents of the history file see sccs-val 1 , and the print subcommand in sccs 1 , since using -z on a truly corrupted file may prevent detection of the error. Add a user name, or a numerical group ID, to the list of users who may check deltas in or out.

If the list is empty, any user is allowed to do so. Delete the indicated flag from the SCCS file. The -d option may be specified only for existing s. See -f for the list of recognized flags. Set the indicated flag to the optional value specified. The following flags are recognized: b Enable branch deltas. When b is set, branches can be created using the -b option of the SCCS get command see sccs-get 1. Set a ceiling on the releases that can be checked out.

If c is not set, the ceiling is Set a floor on the releases that can be checked out. The floor is a number greater than 0 but less than If f is not set, the floor is 1.