You can use

You can use $LD_PRELOAD to override installed versions of a library with a specific version; this is often useful when you are testing a new (or different) library version but don't want to install the replacement library on your system. In general, use the environment variables only while you cre- ate your programs. Don't depend on these environment variables in production, as they have created security issues in the past, so you may not be able to control the values of the variables.

Source Code Control

Version control is an automated process for keeping track of and managing changes made to source code files. Why bother? Because:

One day you will make that one fatal edit to a source file, delete its predecessor, and for- get exactly which line or lines of code you "fixed." Simultaneously keeping track of the current release, the next release, and eight bug fixes manually will become mind-numbing and confusing.

Frantically searching for the backup tape because one of your colleagues overwrote a source file for the fifth time will drive you over the edge. One day, over your morning latte, you will say to yourself, "Version control, it's the Right Thing to Do".

Source Code Control Using RCS

The Revision Control System (RCS) is a common solution to the version control problem. RCS, which is maintained by the GNU project, is available on almost all UNIX systems, not just on Linux. Two alternatives to RCS are the Concurrent Version System (CVS), which also is maintained by the GNU project, and the Source Code Control System (SCCS), a proprietary product.