PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Implementing Version Control
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You can solve all these problems with a version control system. Such systems can
track changes to each file in the repository so that you can see not only the current state
of a file, but also the way it looked at any given time in the past.This feature allows you
to roll back broken code to a known working version.You can tag a particular set of file
instances as a release version, meaning that you can continue development on the code
but get access to a copy of the currently released version at any time.
Version control systems also assist multiple programmers in working on code together.
Each programmer can get a copy of the code in the repository (called checking it out)
and when he makes changes, these changes can be merged back into the repository
(checked in or committed).Version control systems can therefore track who made each
change to a system.
These systems usually have a facility for managing concurrent updates.This means
that two programmers can actually modify the same file at the same time. For example,
imagine that John and Mary have both checked out a copy of the most recent release of
their project. John finishes his changes to a particular file and checks it in. Mary also
changes that file and tries to check it in as well. If the changes they have made are not in
the same part of the file, the version control system will merge the two versions of the
file. If the changes conflict with each other, Mary will be notified and shown the two
different versions. She can then adjust her version of the code to avoid the conflicts.
The version control system used by the majority of Unix and/or open source developers
is the Concurrent Versions System (CVS). CVS, which is open source, comes bundled
with virtually every version of Unix, and you can also get it for PCs running DOS
or Windows and Macs. It supports a client/server model so that you can check code in
or out from any machine with an Internet connection, assuming that the CVS server is
visible on the Internet. It is used for the development of PHP, Apache, and Mozilla,
among other high-profile projects, at least in part for this reason.
You can download CVS for your system from the CVS home page at http://
ximbiot.com/cvs/wiki/.
Although the base CVS system is a command-line tool, various add-ons give it a
more attractive front end, including Java-based and Windows front ends.You can also
access them from the CVS home page.
Bitkeeper is a rival version control product, used by a few high-profile open source
projects including MySQL and the Linux kernel. It is available free to open source
projects from http://www.bitkeeper.com/.
Commercial alternatives are also available. One of them is perforce, which runs on
most common platforms and has PHP support. Although it is commercial, free licenses
are offered for open source projects from the website at http://www.perforce.com/.