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.\"
.if n .ls 2
.if t .tr |\(or
.NH
INTRODUCTION
.PP
This paper describes how to write
programs 
that interface with the
.UC UNIX
operating system in a non-trivial way.
This includes programs that use files by name,
that use pipes,
that invoke other commands as they run,
or that attempt to catch interrupts and other signals
during execution.
.PP
The document collects material which is scattered
throughout several sections of
.I
The
.UC UNIX
Programmer's Manual
.R
[1]
for Version 7
.UC UNIX .
There is no attempt to be complete;
only generally useful material is dealt with.
It is assumed that you will be programming in C,
so you must be able to read the language
roughly up to the level of
.I
The C Programming Language
.R
[2].
Some of the material in sections 2 through 4
is based on
topics covered more carefully there.
You should also be familiar with
.UC UNIX
itself
at least
to the level of
.I
.UC UNIX
for Beginners
.R
[3].
