# Chapter 18. The Source Code Control System

#### Contents:

Introduction
Overview of Commands
Basic Operation
Identification Keywords
Data Keywords
Alphabetical Summary of SCCS Commands
sccs and Pseudo-Commands

This chapter presents the following topics:

- Introduction

- Overview of commands

- Basic operation

- Identification keywords

- Data keywords

- Alphabetical summary of commands

- `sccs` and pseudo-commands

Note: SCCS users who are more familiar with RCS may benefit from the “Conversion Guide for SCCS Users” in Chapter 19, which lists SCCS commands and their RCS equivalents.

For more information, see Applying RCS and SCCS, listed in the Bibliography.

## 18.1. Introduction

The Source Code Control System (SCCS) lets you keep track of each revision of a document, avoiding the confusion that often arises from having several versions of one file online. SCCS is particularly useful when programs are enhanced, but the original version is still needed.

All changes to a file are stored in a file named `s.`file, which is called an SCCS file. Each time a file is “entered” into SCCS, SCCS notes which lines have been changed or deleted since the most recent version. From that information, SCCS can regenerate the file on demand. Each set of changes depends on all previous sets of changes.

Each set of changes is called a delta and is assigned an SCCS identification string (sid). The sid consists of either two components: release and level numbers (in the form a`.`b) or of four components: the release, level, branch, and sequence numbers (in the form a`.`b`.`c`.`d). The branches and sequences are for situations when two on-running versions of the same file are recorded in SCCS. For example, delta 3.2.1.1 refers to release 3, level 2, branch 1, sequence 1.

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