Subversion (SVN) is a centralized storage for sharing information. The Subversion repository is like a time machine. It keeps all the records of every changes ever committed and allows you to explore this history by examining previous versions of files and directories as well as the metadata that accompanies them. With a single Subversion command, you can check out the repository exactly as it was at any date or revision number in the past.
At the core of the Subversion is a repository, which is the central store of that system’s data. Any number of Users connect to the repository, and then read or write to these files according to their permissions. The first Subversion tool we will use is
svnadmin. This tool is for administration tasks, like creating repositories, making backup dumps, and the like.
Creating the Repository
To create a repository, open the command line, change the current directory to where you want to create it, and run
[shell]$ cd /usr/local
$ svnadmin create repo[/shell]
repo = repository name.You can call it whatever you like.
Now the SVN URL is like “svn://localhost:/usr/local/repo“. Subversion uses this repository to store information about your projects, like file revisions.
The svn import command is a quick way to copy an unversioned tree of files into a repository, creating intermediate directories as necessary. svn import doesn’t require a working copy, and your files are immediately committed to the repository. You typically use this when you have an existing tree of files that you want to begin tracking in your Subversion repository. Each project have a recognizable project root in the repository, a directory under which all of the versioned information for that project—and only that project—lives.To create a project under our repository use the following command:
[shell]$ svn mkdir myproject1 svn://localhost:/usr/local/repo[/shell]
Most projects have a recognizable “main line”, or trunk, of development; some branches, which are divergent copies of development lines; and some tags, which are named, stable snapshots of a particular line of development.
Creating trunk,branches and tags
we suggest that each project root contain a
trunk subdirectory for the main development line, a
branches subdirectory in which specific branches (or collections of branches) will be created, and a
tags subdirectory in which specific tags (or collections of tags) will be created.
[shell]$ svn mkdir svn://localhost:/usr/local/repo/myproject1/trunk -m "trunk created"
$ svn mkdir svn://localhost:/usr/local/repo/myproject1/branches -m "branches created"
$ svn mkdir svn://localhost:/usr/local/repo/myproject1/tags -m "tags created"[/shell]
Here “-m” option is using to add the label. Commonly the label is related to the changes or bug fixes which we made in that commit. It is very important to recognize that particular change which we made in each commit. In the above commands we are creating directories, so we gave the label as “trunk created”.
Then we can list the myproject as showing below:
[shell]$ svn list svn://localhost:/usr/local/repo/myproject1[/shell]
We can import our project code to the repository like:
[shell]$ svn import mycode svn://localhost:/usr/local/repo/myproject1/trunk -m "Initial Import"[/shell]
Committed revision 1.[/shell]
Checking out the code
Most of the time, you will start using a Subversion repository by performing a checkout of your project. Checking out a directory from a repository creates a working copy of that directory on your local machine. We can check out the repository by using the following command:
[shell]$ svn checkout svn://localhost:/usr/local/repo/myproject/trunk[/shell]
Checked out revision 1.[/shell]
Subversion chose to create a working copy in a directory named for the final component of the checkout URL. This occurs only as a convenience to the user when the checkout URL is the only bit of information provided to the svn checkout command. Subversion’s command-line client gives you additional flexibility, though, allowing you to optionally specify the local directory name that Subversion should use for the working copy it creates.
[shell]$ svn checkout svn://localhost:/usr/local/repo/myproject/trunk code[/shell]
Checked out revision 1.[/shell]
If there are more developers working in our project, it is better to use the branches. This allows you to save your not-yet-completed work frequently without interfering with others’ changes and while still selectively sharing information with your collaborators.
To Create branches
Creating a branch is very simple. You make a copy of your project tree in the repository using the svn copy command. Since your project’s source code is rooted in the
/repo/myproject/trunk directory, it’s that directory that you’ll copy. You can give the branch name as you wish. Here we are using names of the users.
[shell]$ svn copy svn://localhost:/usr/local/repo/myproject/trunk svn://localhost:/usr/local/repo/myproject/branches/sam -m "branch 1.0.0"[/shell]
[shell] Committed revision 2[/shell]
This command causes a near-instantaneous commit in the repository, creating a new directory in revision 2. The new directory is a copy of
/repo/myproject/trunk. So each user can copy the
/repo/myproject/trunk as their own branch and checkout it like
[shell]$ svn checkout svn://localhost:/usr/local/repo/myproject/branches/sam mycode-sam[/shell]
Checked out revision 2.[/shell]
There’s nothing special about this working copy; it simply mirrors a different directory in the repository. When you commit changes, however, the other users won’t see them when they updates, because they are using their own working copy. Whenever someone needs to make a long-running change that is likely to disrupt the trunk, a standard procedure is to create a private branch and commit changes there until all the work is complete. Subversion gives you the ability to selectively “copy” changes between branches. And when you’re completely finished with your branch, your entire set of branch changes can be copied to the staging branch and checkout this to the staging server for testing. If the code is ready to move to the production server then merge into the production branch and then to production server. If we are doing this first time there is no staging and production branches, so we need to copy the trunk as staging and production branches. After that we have to move the changes in the user branches.
In Subversion terminology, the general act of replicating changes from one branch to another is called merging, and it is performed using the command svn merge.
cd "directory you merge into"
[shell]$ svn switch svn://localhost:/usr/local/repo/myproject/staging
$ svn up
$ svn merge -rAA:BB svn://localhost:/usr/local/repo/myproject/branches/sam
$ svn ci -m ‘Merged branch sam into staging’[/shell]
AA = the revision number of the staging branch
BB = the revision number of the user branch (sam)
Now the staging branch is updated with the user branch, and we can test this code by checking out to the staging server. For this we need to login to the staging server and checkout the code in the correct location.
[shell]$ svn co svn://localhost:/usr/local/repo/myproject/staging /path/to/code[/shell]
Now the code in the staging branch is checked out to the staging server. We have to test this and if all are fine then merge the staging branch to the production branch and then checkout it to the production server as we done with the staging. Also update the trunk with the latest code in the production by merging it with the production branch, because we need to create branches from trunk for the next release. once we have merged the trunk we can retire from the user branch.
Now the trunk is same as the branch “production” repository. Then we have to tag this for the future reference. The tag is used to save the releases which are going to the production. So we can easily track the revisions which we updated to the production.
[shell]$ svn copy svn://localhost:/usr/local/repo/myproject/trunk svn://localhost:/usr/local/repo/myproject/tags/first-release[/shell]
You can give the tag name as you wish. Here we gave the tag name as first-release. This is the flow of branching, you have to repeat these process on the future releases too. Because of using the tag we can easily track the releases. So if any issue occurs it is easy to revert the production.
Some useful commands in svn are given below
svn add – To add files and directories to the repository
svn mkdir – Create a directory in the repository
svn copy - Copy from one location to other
svn move - To rename
svn delete - Delete from the repository
svn ci - Commit the changes in the working copy
svn diff – Shows line-level details of a particular change
svn log – Shows you broad information: log messages with date and author information attached to revisions and which paths changed in each revision
svn cat – Retrieves a file as it existed in a particular revision number and displays it on your screen
svn list – Displays the files in a directory for any given revision
svn log – Examine merge-sensitive history
Subversion has commands to help you maintain parallel branches of your files and directories. It allows you to create branches by copying your data, and remembers that the copies are related to one another. The main advantage of branching is that the users can work independently with their own repository and so it will not affect the other users and also easy to maintain.