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By Root 1346 0

is a powerful and customizable user interface within itself. The user can easily redefine keys and commands to fit her needs; you don't need to provide these customization features yourself. As long as the text interface of the program is straightforward enough to interact with Emacs, customization is not difficult to accomplish. In addition, many users prefer to do virtually everything within Emacs—from reading electronic mail and news to compiling and debugging programs. Giving your program an Emacs frontend allows it to be used more easily by people with this mind-set. It also allows your program to interact with other programs running under Emacs—for example, you can easily cut and paste between different Emacs text buffers. You can even write entire programs using Emacs LISP, if you wish.

Revision Control Tools: RCS

Revision Control System (RCS) has been ported to Linux. This is a set of programs that allow you to maintain a "library" of files that records a history of revisions, allows source-file locking (in case several people are working on the same project), and automatically keeps track of source-file version numbers. RCS is typically used with program source code files, but is general enough to be applicable to any type of file where multiple revisions must be maintained.

Why bother with revision control ? Many large projects require some kind of revision control in order to keep track of many tiny complex changes to the system. For example, attempting to maintain a program with a thousand source files and a team of several dozen programmers would be nearly impossible without using something like RCS. With RCS, you can ensure that only one person may modify a given source file at any one time, and all changes are checked in along with a log message detailing the change.

RCS is based on the concept of an RCS file, a file that acts as a "library" where source files are "checked in" and "checked out." Let's say that you have a source file importrtf.c that you want to maintain with RCS. The RCS filename would be importrtf.c,v by default. The RCS file contains a history of revisions to the file, allowing you to extract any previous checked-in version of the file. Each revision is tagged with a log message that you provide.

When you check in a file with RCS, revisions are added to the RCS file, and the original file is deleted by default. To access the original file, you must check it out from the RCS file. When you're editing a file, you generally don't want someone else to be able to edit it at the same time. Therefore, RCS places a lock on the file when you check it out for editing. Only you, the person who checked out this locked file, can modify it (this is accomplished through file permissions). Once you're done making changes to the source, you check it back in, which allows anyone working on the project to check it back out again for further work. Checking out a file as unlocked does not subject it to these restrictions; generally, files are checked out as locked only when they are to be edited but are checked out as unlocked just for reading (for example, to use the source file in a program build).

RCS automatically keeps track of all previous revisions in the RCS file and assigns incremental version numbers to each new revision that you check in. You can also specify a version number of your own when checking in a file with RCS; this allows you to start a new "revision branch" so that multiple projects can stem from different revisions of the same file. This is a good way to share code between projects but ensure that changes made to one branch won't be reflected in others.

Here's an example. Take the source file importrtf.c, which contains our friendly program:

#include

int main(void) {

printf("Hello, world!");

}

The first step is to check it into RCS with the ci command:

papaya$ ci importrtf.c

importrtf.c,v <-- importrtf.c

enter description, terminated with single '.' or end of file:

NOTE: This is NOT the log message!

>> Hello world source code

>> .

initial revision: