6.1. Introduction

A UNIX system requires numerous data files for normal operation: the password file /etc/passwd and the group file /etc/group are two files that are frequently used by various programs. For example, the password file is used every time a user logs in to a UNIX system and every time someone executes an ls -l command.

Historically, these data files have been ASCII text files and were read with the standard I/O library. But for larger systems, a sequential scan through the password file becomes time consuming. We want to be able to store these data files in a format other than ASCII text, but still provide an interface for an application program that works with any file format. The portable interfaces to these data files are the subject of this chapter. We also cover the system identification functions and the time and date functions.