SVN Quick Guide

Advertisements


SVN Basic Concepts

What is Version Control System (VCS) ?

Version Control System is a software that helps software developers to work together and also maintains complete history of their work.

Following are goals of Version Control System.

  • Allow developers to work simultaneously.

  • Do not overwrite each other’s changes.

  • Maintain history of every version of everything.

Version control system is divided into two categories.

  • Centralized version control system (CVCS) and

  • Distributed/Decentralized version control system (DVCS)

In this tutorial session we will concentrate only on Centralized Version Control System and especially Subversion. Subversion falls under centralized version control system, meaning that it uses central server to store all files and enables team collaboration.

Version Control Terminologies

Let us start by discussing some of the terms that we will be using in our tutorial.

  • The Repository: A repository is the heart of any version control system. It is central place where developers store all their work. Repository not only stores files but also history. Repository is accessed over a network, with repository acting as a sever and version control tool acting as a client. Client can connect to repository, and then they can store/retrieve their changes to/from repository. By storing changes, a client makes available these changes to other people and by retrieving changes; a client takes other people changes as a working copy.

  • Trunk: The trunk is a directory where all the main development happens and is usually checked out by developers to work on the project.

  • Tags: The tags directory is used to store named snapshots of the project. Tag operation allows to give descriptive and memorable names to specific version in the repository.

    For example LAST_STABLE_CODE_BEFORE_EMAIL_SUPPORT is more memorable than

    Repository UUID: 7ceef8cb-3799-40dd-a067-c216ec2e5247 and

    Revision: 13

  • Branches: Brach operation is used to create another line of development. It is useful when you want your development process to fork off into two different directions. For example, when you release version 5.0, you might want to create a branch so that development of 6.0 features can be kept separate from 5.0 bug-fixes.

  • Working copy: Working copy is a snapshot of the repository. The repository is shared by all the team, but people do not modify it directly. Instead each developer checkout working copy. The working copy is private workplace where developer can do their work within isolated from the rest of the team.

  • Commit changes: Commit is a process of storing changes from private workplace to central server. After commit, changes are made available to all the team. Other developer can retrieve these changes by updating their working copy. Commit is atomic operation. Either whole commit succeeds or is rolled back. Users never see half finished commit.

SVN Environment Setup

SVN Installation

Subversion is popular open-source Version Control tool. As it’s open-source it is available for free over a internet. It comes by default with most of the GNU/Linux distributions, so it might be already installed on your system. To check whether it is installed or not use following command.

[jerry@CentOS ~]$ svn --version

If Subversion client is not installed, then command will report error, otherwise it will display version of the installed software.

[jerry@CentOS ~]$ svn --version
-bash: svn: command not found

If you are using RPM based GNU/Linux then use yum command for installation. After successful installation execute svn --version command.

[jerry@CentOS ~]$ su -
Password: 
[root@CentOS ~]# yum install subversion

[jerry@CentOS ~]$ svn --version
svn, version 1.6.11 (r934486)
compiled Jun 23 2012, 00:44:03

And if you are using Debian based GNU/Linux then use apt command for installation.

[jerry@Ubuntu]$ sudo apt-get update
[sudo] password for jerry:

[jerry@Ubuntu]$ sudo apt-get install subversion

[jerry@Ubuntu]$ svn --version
svn, version 1.7.5 (r1336830)
compiled Jun 21 2013, 22:11:49

Apache Setup

We have seen how to install Subversion client on GNU/Linux. Let us see how to create new repository and allow access to users.

On server we have to install Apache httpd module and svnadmin tool.

[jerry@CentOS ~]$ su -
Password: 
[root@CentOS ~]# yum install mod_dav_svn subversion

The mod_dav_svn package allows access to a repository using HTTP, via the Apache httpd server and subversion package installs svnadmin tool.

Subversion reads it's configuration from /etc/httpd/conf.d/subversion.conf file. After adding configuration subversion.conf file will look like this.

LoadModule dav_svn_module     modules/mod_dav_svn.so
LoadModule authz_svn_module   modules/mod_authz_svn.so

<Location /svn>
   DAV svn
   SVNParentPath /var/www/svn
   AuthType Basic
   AuthName "Authorization Realm"
   AuthUserFile /etc/svn-users
   Require valid-user
</Location>

Let us create Subversion users and grant them access to the repository. htpasswd command is used to create and update the plain-text files which are used to store usernames and passwords for basic authentication of HTTP users. '-c' options creates password file, if password file already exists, it is overwritten. That is why use '-c' option only first time. '-m' option enables MD5 encryption for passwords.

User Setup

Let us create user tom.

[root@CentOS ~]# htpasswd -cm /etc/svn-users tom
New password: 
Re-type new password: 
Adding password for user tom

Let us create user jerry

[root@CentOS ~]# htpasswd -m /etc/svn-users jerry
New password: 
Re-type new password: 
Adding password for user jerry
[root@CentOS ~]# 

Create Subversion parent directory to store all work (see /etc/httpd/conf.d/subversion.conf).

[root@CentOS ~]# mkdir /var/www/svn
[root@CentOS ~]# cd /var/www/svn/

Repository Setup

Create project repository named project_repo. svnadmin command will create new repository and few other directories inside that to store metadata.

[root@CentOS svn]# svnadmin create project_repo

[root@CentOS svn]# ls -l project_repo
total 24
drwxr-xr-x. 2 root root 4096 Aug  4 22:30 conf
drwxr-sr-x. 6 root root 4096 Aug  4 22:30 db
-r--r--r--. 1 root root    2 Aug  4 22:30 format
drwxr-xr-x. 2 root root 4096 Aug  4 22:30 hooks
drwxr-xr-x. 2 root root 4096 Aug  4 22:30 locks
-rw-r--r--. 1 root root  229 Aug  4 22:30 README.txt

Let us change user and group ownership of the repository.

[root@CentOS svn]# chown -R apache.apache project_repo/

Check whether SELinux is enabled or not using SELinux status tool.

[root@CentOS svn]# sestatus
SELinux status:                 enabled
SELinuxfs mount:                /selinux
Current mode:                   enforcing
Mode from config file:          enforcing
Policy version:                 24
Policy from config file:        targeted

For our server SELinux is enabled, so we have to change SELinux security context.

[root@CentOS svn]# chcon -R -t httpd_sys_content_t /var/www/svn/project_repo/

To allow commits over HTTP execute following command.

[root@CentOS svn]# chcon -R -t httpd_sys_rw_content_t /var/www/svn/project_repo/

Restart the Apache server and we are done with configuration of Apache server.

[root@CentOS svn]# service httpd restart
Stopping httpd:                                            [FAILED]
Starting httpd: httpd: apr_sockaddr_info_get() failed for CentOS
httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for ServerName
                                                           [  OK  ]
[root@CentOS svn]# service httpd status
httpd (pid  1372) is running...
[root@CentOS svn]#

We have configured Apache server successfully, now configure repository. To provide repository access to only authenticated users and to use default authorization file; append following lines to project_repo/conf/svnserve.conf file.

anon-access = none
authz-db = authz

By conventionally every Subversion project have trunk, tags and branches directories directly under the project's root directory.

The trunk is a directory where all the main development happens and is usually checked out by developers to work on the project.

The tags directory is used to store named snapshots of the project. When creating a production release, the team will tag the code that goes into the release.

The branches directory is used when you want to pursue different lines of development.

Let us create trunk, tags and branches directory structure under project repository.

[root@CentOS svn]# mkdir /tmp/svn-template
[root@CentOS svn]# mkdir /tmp/svn-template/trunk
[root@CentOS svn]# mkdir /tmp/svn-template/branches
[root@CentOS svn]# mkdir /tmp/svn-template/tags

Now import directories from /tmp/svn-template to the repository.

[root@CentOS svn]# svn import -m 'Create trunk, branches, tags directory structure' /tmp/svn-template/ 
Adding         /tmp/svn-template/trunk
Adding         /tmp/svn-template/branches
Adding         /tmp/svn-template/tags
Committed revision 1.
[root@CentOS svn]#

Done!!! . We have created repository successfully and allowed access to Tom and Jerry. From now they can perform all supported operation to the repository.

Life Cycle

In this chapter we will discuss about life cycle of a Version Control System. In later chapters we will see Subversion command for each operation.

Create repository:

The repository is a central place where developers store all their work. Repository not only stores files but also history about changes. Meaning it maintains history of who did changes, in which files, when and why ?

The create operation is used to create a new repository. Most of the times this operation is done only once. When you create a new repository, your VCS will expect you to say something to identify it, such as where you want it to be created, or what it's name should be.

Checkout:

checkout operation is used to create a working copy from the repository. Working copy is a private workplace where developers do their changes and later on submit these changes to repository.

Update:

As name suggests update operation is used to update working copy. This operation synchronizes working copy with the repository. As repository is shared by all the team other developers can commit their changes and your working copy becomes older.

Let us suppose Tom and Jerry two developers working on a project. Both checkouts the latest version from repository and start working. At this point their working copies are completely synchronized with the repository. Jerry completes his work very efficiently and commits his changes to the repository.

Now Tom's working copy is out of date. Update operation will pull Jerry’s latest changes from the repository and will update Tom's working copy.

Perform changes:

After checkout one can do various operations to perform changes. Edit is the most common operation. One can edit existing file to add/remove contents from file.

One can add files/directories. But immediately these files/directories do not become part of repository, instead they are added to the pending change-list and become part of repository after commit operation.

Similarly one can delete files/directories. Delete operation immediately deletes file from working copy, but actual deletion of file added to the pending change-list and changes made to the repository after commit operation.

Rename operation changes the name of the file/directory. Move operation is used to move files/directories from one place to another in a repository tree.

Review changes:

When you checkout the working copy or update working copy then your working copy is completely synchronized with the repository. But as you do changes to your working copy it becomes newer than the repository. And it's good practice to review your changes before commit operation.

Status operation lists the modifications that have been made to the working copy. As I mentioned before, whenever you do changes in working copy all these changes become part of pending change-list. And status operation is used to see the pending change-list.

Status operation only provides a list of changes but not details about them. One can use diff operation to view the details of the modifications that have been made to the working copy.

Fix mistakes:

Let us suppose one has made changes to his working copy, but now he want to throw away these changes. In this situation revert operation will help.

Revert operation undo modifications that have been made to the working copy. It is possible to revert one or more files/directories. Also it is possible to revert whole working copy, in this case revert operation will destroy the pending change-list and will bring working copy back to its original state.

Resolve conflicts:

Conflicts can occur at the time of merging. But what is conflict ? Merge operation automatically handles everything that can be done safely. Everything else is considered as conflict. For example, what if "hello.c" file was modified in branch and deleted in another branch ? Such a situation requires a person to make the decision. The resolve operation is used to help the user figure things out and to inform VCS how the conflicts should be handled.

Commit changes:

Commit operation is used to apply changes from working copy to the repository. This operation modifies the repository and other developers can see these changes by updating their working copy.

Before commit one has to add files/directories to pending change-list. This is the place where changes wait to be committed. With commit we usually provide a log message to explain why someone made changes. This log message becomes part of the history of the repository. Commit is a atomic operation. Meaning either whole commit succeeds or is rolled back. Users never see half finished commit.

Checkout Process

Subversion provides checkout command to check out a working copy from a repository. Below command will create new directory in current working directory with name project_repo. Don't bother about repository URL, most of the time it is already provided by Subversion administrator with appropriate access.

[tom@CentOS ~]$ svn checkout http://svn.server.com/svn/project_repo --username=tom

Above command will produce following result

A    project_repo/trunk
A    project_repo/branches
A    project_repo/tags
Checked out revision 1.

After every successful checkout operation; revision number will get printed. If you want to view more information about the repository. Then execute info command.

[tom@CentOS trunk]$ pwd
/home/tom/project_repo/trunk

[tom@CentOS trunk]$ svn info

Above command will produce following result

Path: .
URL: http://svn.server.com/svn/project_repo/trunk
Repository Root: http://svn.server.com/svn/project_repo
Repository UUID: 7ceef8cb-3799-40dd-a067-c216ec2e5247
Revision: 1
Node Kind: directory
Schedule: normal
Last Changed Author: jerry
Last Changed Rev: 0
Last Changed Date: 2013-08-24 18:15:52 +0530 (Sat, 24 Aug 2013)

[tom@CentOS trunk]$ 

Perform Changes

Jerry checkouts the latest version of the repository and starts working on a project. He creates array.c file inside trunk directory.

[jerry@CentOS ~]$ cd project_repo/trunk/

[jerry@CentOS trunk]$ cat array.c

Above command will produce following result

#include <stdio.h>

#define MAX 16

int main(void)
{
   int i, n, arr[MAX];

   printf("Enter the total number of elements: ");
   scanf("%d", &n);

   printf("Enter the elements\n");

   for (i = 0; i < n; ++i)
      scanf("%d", &arr[i]);

   printf("Array has following elements\n");
   for (i = 0; i < n; ++i)
      printf("|%d| ", arr[i]);
   
   printf("\n");

   return 0;
}

He wants to test his code before commit

[jerry@CentOS trunk]$ make array
cc     array.c   -o array

[jerry@CentOS trunk]$ ./array 
Enter the total number of elements: 5
Enter the elements
1
2
3
4
5
Array has following elements
|1| |2| |3| |4| |5| 

He compiled and tested his code and everything is working as expected, now it's time to commit changes.

[jerry@CentOS trunk]$ svn status
?       array.c
?       array

Subversion is showing ? infront of filenames because it doesn't know what to do with these files.

Before commit Jerry needs to add this file to the pending change-list.

[jerry@CentOS trunk]$ svn add array.c 
A         array.c

Let us check it with status operation. Subversion shows A before array.c it means file is successfully added to the pending change-list.

[jerry@CentOS trunk]$ svn status
?       array
A       array.c

To store array.c file to the repository use commit command with -m option followed by commit message. If you omit -m option Subversion will bring up text editor where you can type a multi-line message.

[jerry@CentOS trunk]$ svn commit -m "Initial commit"
Adding         trunk/array.c
Transmitting file data .
Committed revision 2.

Now array.c file is successfully added to the repository and revision number is incremented by one.

Review Changes

Jerry already added array.c file to the repository. Tom also checkouts the latest code and starts workings.

[tom@CentOS ~]$ svn co http://svn.server.com/svn/project_repo --username=tom

Above command will produce following result

A    project_repo/trunk
A    project_repo/trunk/array.c
A    project_repo/branches
A    project_repo/tags
Checked out revision 2.

But he founds that, someone has already added code. So he is curious about who did that and he checks the log message to see more details using the following command:

[tom@CentOS trunk]$ svn log

Above command will produce following result

------------------------------------------------------------------------
r2 | jerry | 2013-08-17 20:40:43 +0530 (Sat, 17 Aug 2013) | 1 line

Initial commit
------------------------------------------------------------------------
r1 | jerry | 2013-08-04 23:43:08 +0530 (Sun, 04 Aug 2013) | 1 line

Create trunk, branches, tags directory structure
------------------------------------------------------------------------

When Tom observes Jerry’s code. He immediately notices a bug into that. Jerry was not checking for array overflow, this will cause serious problem. So Tom decides to fix this problem. After modification array.c will look like this.

#include <stdio.h>

#define MAX 16

int main(void)
{
   int i, n, arr[MAX];

   printf("Enter the total number of elements: ");
   scanf("%d", &n);

   /* handle array overflow condition */
   if (n > MAX) {
      fprintf(stderr, "Number of elements must be less than %d\n", MAX);
      return 1;
   }

   printf("Enter the elements\n");

   for (i = 0; i < n; ++i)
      scanf("%d", &arr[i]);

   printf("Array has following elements\n");
   for (i = 0; i < n; ++i)
      printf("|%d| ", arr[i]);
      printf("\n");

   return 0;
}

Tom wants to use the status operation to see the pending change-list.

[tom@CentOS trunk]$ svn status
M       array.c

array.c file is modified, that's why Subversion shows M letter before file name. Next Tom compiles and tests his code and it's working fine. Before committing changes he wants to double-check it by reviewing the changes that he made.

[tom@CentOS trunk]$ svn diff
Index: array.c
===================================================================
--- array.c   (revision 2)
+++ array.c   (working copy)
@@ -9,6 +9,11 @@
    printf("Enter the total number of elements: ");
    scanf("%d", &n);
 
+   if (n > MAX) {
+      fprintf(stderr, "Number of elements must be less than %d\n", MAX);
+      return 1;
+   }
+
    printf("Enter the elements\n");
 
    for (i = 0; i < n; ++i)

Tom added few lines in array.c file that's why Subversion shows + sign before new lines. Now he is ready to commit his changes.

[tom@CentOS trunk]$ svn commit -m "Fix array overflow problem"

Above command will produce following result

Sending        trunk/array.c
Transmitting file data .
Committed revision 3.

Tom's changes successfully committed to the repository.

Update Process

Jerry had committed first version of the code. But he thinks that he should write two functions to accept input and to display array contents. After modification array.c will look like this.

#include <stdio.h>

#define MAX 16

void accept_input(int *arr, int n)
{
   int i;

   for (i = 0; i < n; ++i)
      scanf("%d", &arr[i]);
}

void display(int *arr, int n)
{
   int i;

   for (i = 0; i < n; ++i)
      printf("|%d| ", arr[i]);
   
   printf("\n");
}

int main(void)
{
   int i, n, arr[MAX];

   printf("Enter the total number of elements: ");
   scanf("%d", &n);

   printf("Enter the elements\n");
   accept_input(arr, n);

   printf("Array has following elements\n");
   display(arr, n);

   return 0;
}

Jerry compiles and tests his code and ready to commit changes. Before that he wants to review changes using the following command.

[jerry@CentOS trunk]$ svn diff

Above command will produce following result

Index: array.c
===================================================================
--- array.c   (revision 2)
+++ array.c   (working copy)
@@ -2,6 +2,24 @@
 
 #define MAX 16
 
+void accept_input(int *arr, int n)
+{
+   int i;
+
+   for (i = 0; i & n; ++i)
+      scanf("%d", &arr[i]);
+}
+
+void display(int *arr, int n)
+{
+   int i;
+
+   for (i = 0; i < n; ++i)
+      printf("|%d| ", arr[i]);
+   
+   printf("\n");
+}
+
 int main(void)
 {
    int i, n, arr[MAX];
@@ -10,15 +28,10 @@
    scanf("%d", &n);
 
    printf("Enter the elements\n");
+   accept_input(arr, n);
 
-   for (i = 0; i < n; ++i)
-      scanf("%d", &arr[i]);
-
    printf("Array has following elements\n");
-   for (i = 0; i < n; ++i)
-      printf("|%d| ", arr[i]);
-   
-   printf("\n");
+   display(arr, n);
 
    return 0;
 }

For new added lines Subversion shows + sign before line and for removed line it shows - sign. Jerry try to commit the changes using the following command:

[jerry@CentOS trunk]$ svn commit -m "Add function to accept input and to display array contents"

Above command will produce following result

Sending        trunk/array.c
svn: Commit failed (details follow):
svn: File or directory 'array.c' is out of date; try updating
svn: resource out of date; try updating

Subversion is not allowing committing Jerry's changes, because Tom already modified the repository and Jerry's working copy is out of date. To avoid overwriting each other's changes Subversion fails this operation. Jerry must update working copy before committing his changes. So he uses update command as shown

[jerry@CentOS trunk]$ svn update
G    array.c
Updated to revision 3.

Subversion is showing G letter before filename, meaning this file has been merged.

[jerry@CentOS trunk]$ svn diff

Above command will produce following result

Index: array.c
===================================================================
--- array.c   (revision 3)
+++ array.c   (working copy)
@@ -2,6 +2,24 @@
 
 #define MAX 16
 
+void accept_input(int *arr, int n)
+{
+   int i;
+
+   for (i = 0; i < n; ++i)
+      scanf("%d", &arr[i]);
+}
+
+void display(int *arr, int n)
+{
+   int i;
+
+   for (i = 0; i < n; ++i)
+      printf("|%d| ", arr[i]);
+   
+   printf("\n");
+}

+
 int main(void)
 {
    int i, n, arr[MAX];
@@ -15,15 +33,10 @@
    }
 
    printf("Enter the elements\n");
+   accept_input(arr, n);
 
-   for (i = 0; i < n; ++i)
-      scanf("%d", &arr[i]);
-
    printf("Array has following elements\n");
-   for (i = 0; i < n; ++i)
-      printf("|%d| ", arr[i]);
-   
-   printf("\n");
+   display(arr, n);
 
    return 0;
 }

Subversion is showing only Jerry's changes. But array.c file is merged, if you observe carefully Subversion now showing revision number 3, In previous output it was showing revision number 2. Just review who made changes in the file and for what purpose.

jerry@CentOS trunk]$ svn log
------------------------------------------------------------------------
r3 | tom | 2013-08-18 20:21:50 +0530 (Sun, 18 Aug 2013) | 1 line

Fix array overflow problem
------------------------------------------------------------------------
r2 | jerry | 2013-08-17 20:40:43 +0530 (Sat, 17 Aug 2013) | 1 line

Initial commit
------------------------------------------------------------------------
r1 | jerry | 2013-08-04 23:43:08 +0530 (Sun, 04 Aug 2013) | 1 line

Create trunk, branches, tags directory structure
------------------------------------------------------------------------

Now Jerry's working copy is synchronized with the repository and he can safely commit his changes.

[jerry@CentOS trunk]$ svn commit -m "Add function to accept input and to display array contents"
Sending        trunk/array.c
Transmitting file data .
Committed revision 4.

Fix Mistakes

Suppose Jerry accidently modifies array.c file and he is getting compilation errors. Now he wants to throw away changes. In this situation revert operation will help. Revert operation will undo any local changes to a file or directory and resolve any conflicted states.

[jerry@CentOS trunk]$ svn status

Above command will produce following result

M       array.c

Let's try to make array as follows:

[jerry@CentOS trunk]$ make array

Above command will produce following result

cc     array.c   -o array
array.c: In function ‘main’:
array.c:26: error: ‘n’ undeclared (first use in this function)
array.c:26: error: (Each undeclared identifier is reported only once
array.c:26: error: for each function it appears in.)
array.c:34: error: ‘arr’ undeclared (first use in this function)
make: *** [array] Error 1

Jerry performs revert operation on array.c file

[jerry@CentOS trunk]$ svn revert array.c 
Reverted 'array.c'

[jerry@CentOS trunk]$ svn status
[jerry@CentOS trunk]$

Now compile the code.

[jerry@CentOS trunk]$ make array
cc     array.c   -o array

After revert operation his working copy is back to it's original state. Revert operation can revert single file as well as complete directory.To revert a directory user -R option as shown below

[jerry@CentOS project_repo]$ pwd
/home/jerry/project_repo

[jerry@CentOS project_repo]$ svn revert -R trunk

Till now we have seen how to revert changes which has been made to working copy. But what if you want to revert committed revision. Version Control System tool doesn't allow to delete history from the repository. We can only append history. It will happen even you delete file from the repository. To undo an old revision, we have to reverse whatever changes were made in the old revision and then commit a new revision. This is called a reverse merge.

Let us suppose Jerry add code for linear search operation. After verification he commits his changes.

[jerry@CentOS trunk]$ svn diff
Index: array.c
===================================================================
--- array.c   (revision 21)
+++ array.c   (working copy)
@@ -2,6 +2,16 @@
 
 #define MAX 16
 
+int linear_search(int *arr, int n, int key)
+{
+   int i;
+
+   for (i = 0; i < n; ++i)
+      if (arr[i] == key)
+         return i;
+   return -1;
+}
+
 void bubble_sort(int *arr, int n)
 {
    int i, j, temp, flag = 1;

[jerry@CentOS trunk]$ svn status
?       array
M       array.c

[jerry@CentOS trunk]$ svn commit -m "Added code for linear search"
Sending        trunk/array.c
Transmitting file data .
Committed revision 22.

Jerry is curious about what Tom is doing. So he checks Subversion log messages.

[jerry@CentOS trunk]$ svn log

Above command will produce following result

------------------------------------------------------------------------
r5 | tom | 2013-08-24 17:15:28 +0530 (Sat, 24 Aug 2013) | 1 line

Add binary search operation
------------------------------------------------------------------------
r4 | jerry | 2013-08-18 20:43:25 +0530 (Sun, 18 Aug 2013) | 1 line

Add function to accept input and to display array contents

After viewing log messages, Jerry realizes that he did serious mistake. Because Tom already implemented binary search operation and which is better than linear search. Means his code is redundant, now Jerry has to revert his changes to previous revision. So first find the current revision of the repository. Currently repository is at revision 22 and we to revert it to previous revision i.e. revision 21.

[jerry@CentOS trunk]$ svn up
At revision 22.

[jerry@CentOS trunk]$ svn merge -r 22:21 array.c 
--- Reverse-merging r22 into 'array.c':
U    array.c

[jerry@CentOS trunk]$ svn commit -m "Reverted to revision 21"
Sending        trunk/array.c
Transmitting file data .
Committed revision 23.

Resolve Conflicts

Tom decides to add README file for their project. So he creates README file and adds TODO list into that. After adding this file repository is at revision 6.

[tom@CentOS trunk]$ cat README 
/* TODO: Add contents in README file */

[tom@CentOS trunk]$ svn status
?       README

[tom@CentOS trunk]$ svn add README 
A         README

[tom@CentOS trunk]$ svn commit -m "Added README file. Will update it's content in future."
Adding         trunk/README
Transmitting file data .
Committed revision 6. 

Jerry checkouts the latest code which is at revision 6. And immediately he starts working. After few hours Tom updates README file and commits his changes. Modified README will look like this.

[tom@CentOS trunk]$ cat README 
* Supported operations:

1) Accept input
2) Display array elements

[tom@CentOS trunk]$ svn status
M       README

[tom@CentOS trunk]$ svn commit -m "Added supported operation in README"
Sending        trunk/README
Transmitting file data .
Committed revision 7.

Now repository is at revision 7 and Jerry's working copy is out of date. Jerry also updates README file and tries to commit his changes.

Jerry's README file looks like this.

[jerry@CentOS trunk]$ cat README 
* File list

1) array.c	Implementation of array operation.
2) README	Instructions for user.

[jerry@CentOS trunk]$ svn status
M       README

[jerry@CentOS trunk]$ svn commit -m "Updated README"
Sending        trunk/README
svn: Commit failed (details follow):
svn: File or directory 'README' is out of date; try updating
svn: resource out of date; try updating

Step 1: View Conflicts

This is good. Subversion has detected that README file has changed since last updated. So Jerry has to update his working copy.

[jerry@CentOS trunk]$ svn up
Conflict discovered in 'README'.
Select: (p) postpone, (df) diff-full, (e) edit,
        (mc) mine-conflict, (tc) theirs-conflict,
        (s) show all options:

Subversion is complaining that there is a conflict with the README file, and Subversion does not know how to solve this. So Jerry chooses the df option to review the conflict.

[jerry@CentOS trunk]$ svn up
Conflict discovered in 'README'.
Select: (p) postpone, (df) diff-full, (e) edit,
        (mc) mine-conflict, (tc) theirs-conflict,
        (s) show all options: df
--- .svn/text-base/README.svn-base	Sat Aug 24 18:07:13 2013
+++ .svn/tmp/README.tmp	Sat Aug 24 18:13:03 2013
@@ -1 +1,11 @@
-/* TODO: Add contents in README file */
+<<<<<<< .mine
+* File list
+
+1) array.c	Implementation of array operation.
+2) README	Instructions for user.
+=======
+* Supported operations:
+
+1) Accept input
+2) Display array elements
+>>>>>>> .r7
Select: (p) postpone, (df) diff-full, (e) edit, (r) resolved,
        (mc) mine-conflict, (tc) theirs-conflict,
        (s) show all options:

Step 2: Postpone Conflicts

Next Jerry chooses the postpone(p) options, so he can resolve the conflict.

Select: (p) postpone, (df) diff-full, (e) edit, (r) resolved,
        (mc) mine-conflict, (tc) theirs-conflict,
        (s) show all options: p
C    README
Updated to revision 7.
Summary of conflicts:
  Text conflicts: 1

After opening README in text editor he realises that Subversion has included both Tom's code and his code with conflict markers.

[jerry@CentOS trunk]$ cat README
<<<<<<< .min
* File list

1) array.c	Implementation of array operation.
2) README	Instructions for user.
=======
* Supported operations:

1) Accept input
2) Display array elements
>>>>>>> .r7

Jerry wants Tom's changes as well as his, so he just removes the lines containing the conflict markers.

So modified README will look like this.

[jerry@CentOS trunk]$ cat README
* File list

1) array.c	Implementation of array operation.
2) README	Instructions for user.

* Supported operations:

1) Accept input
2) Display array elements

Jerry resolved conflict and he retries commit.

[jerry@CentOS trunk]$ svn commit -m "Updated README"
svn: Commit failed (details follow):
svn: Aborting commit: '/home/jerry/project_repo/trunk/README' remains in conflict
 
[jerry@CentOS trunk]$ svn status
?       README.r6
?       README.r7
?       README.mine
C       README

Step 3: Resolve Conflicts

Here C letters indicates that there is conflicts in README file. Jerry resolved the conflict but didn't tell Subversion that he had resolved conflict. He uses resolve command to inform Subversion about conflict resolution.

[jerry@CentOS trunk]$ svn resolve --accept=working README
Resolved conflicted state of 'README'

[jerry@CentOS trunk]$ svn status
M       README

[jerry@CentOS trunk]$ svn commit -m "Updated README"
Sending        trunk/README
Transmitting file data .
Committed revision 8.

Tags

Version Control System supports tag operation by using that one can give meaningful name to specific version of the code. Tag allows to give descriptive and memorable names to specific version of code. For example BASIC_ARRAY_OPERATIONS is more memorable than revision 4.

Let us see tag operation with example. Tom decides to create a tag so he can access code more easily.

[tom@CentOS project_repo]$ svn copy --revision=4 trunk/ tags/basic_array_operations

Above command will produce following result

A    tags/basic_array_operations/array.c
Updated to revision 4.
A         tags/basic_array_operations

Upon successful completion, new directory will be created inside tags directory.

[tom@CentOS project_repo]$ ls -l tags/
total 4
drwxrwxr-x. 3 tom tom 4096 Aug 24 18:18 basic_array_operations

Tom wants to double-check it before commit. Status operation is showing that tag operation is successful, so he can safely commit his changes.

[tom@CentOS project_repo]$ svn status
A  +    tags/basic_array_operations

[tom@CentOS project_repo]$ svn commit -m "Created tag for basic array operations"
Adding         tags/basic_array_operations

Committed revision 5.

Branching

Branch operation creates another line of development. It is useful when someone wants development process to fork off into two different direction. Let us suppose you released product of version 1.0, you might want to create new branch so that development of 2.0 can be kept separate from 1.0 bug fixes.

In this section we will see how to create, traverse and merge branch. Jerry already frustrated because of conflict, so he decides to create new private branch.

[jerry@CentOS project_repo]$ ls
branches  tags  trunk

[jerry@CentOS project_repo]$ svn copy trunk branches/jerry_branch
A         branches/jerry_branch

[jerry@CentOS project_repo]$ svn status
A  +    branches/jerry_branch

[jerry@CentOS project_repo]$ svn commit -m "Jerry's private branch"
Adding         branches/jerry_branch
Adding         branches/jerry_branch/README

Committed revision 9.
[jerry@CentOS project_repo]$ 

Now Jerry is working in his private branch. He adds sort operation for array. Jerry's modified code looks like this.

[jerry@CentOS project_repo]$ cd branches/jerry_branch/

[jerry@CentOS jerry_branch]$ cat array.c 

Above command will produce following result

#include <stdio.h>

#define MAX 16

void bubble_sort(int *arr, int n)
{

   int i, j, temp, flag = 1;

   for (i = 1; i < n && flag == 1; ++i) {
      flag = 0;
      for (j = 0; j < n - i; ++j) {
         if (arr[j] > arr[j + 1]) {
            flag      	= 1;
            temp      	= arr[j];
            arr[j]      = arr[j + 1];
            arr[j + 1]	= temp;
         }
      }
   }
}

void accept_input(int *arr, int n)
{
   int i;

   for (i = 0; i < n; ++i)
      scanf("%d", &arr[i]);
}

void display(int *arr, int n)
{
   int i;

   for (i = 0; i < n; ++i)
      printf("|%d| ", arr[i]);

   printf("\n");
}

int main(void)
{
   int i, n, key, ret, arr[MAX];

   printf("Enter the total number of elements: ");
   scanf("%d", &n);

   /* Error handling for array overflow */
   if (n >MAX) {
      fprintf(stderr, "Number of elements must be less than %d\n", MAX);
      return 1;
   }

   printf("Enter the elements\n");
   accept_input(arr, n);

   printf("Array has following elements\n");
   display(arr, n);

   printf("Sorted data is\n");
   bubble_sort(arr, n);
   display(arr, n);

   return 0;
}

Jerry compiles and tests his code and ready to commit his changes.

[jerry@CentOS jerry_branch]$ make array
cc     array.c   -o array

[jerry@CentOS jerry_branch]$ ./array 

Above command will produce following result

Enter the total number of elements: 5
Enter the elements
10
-4
2
7 
9
Array has following elements
|10| |-4| |2| |7| |9| 
Sorted data is
|-4| |2| |7| |9| |10| 

[jerry@CentOS jerry_branch]$ svn status
?       array
M       array.c

[jerry@CentOS jerry_branch]$ svn commit -m "Added sort operation"
Sending        jerry_branch/array.c
Transmitting file data .
Committed revision 10.


Advertisements
Advertisements