.if n .ls 2.if t .tr |\(or.NHINTRODUCTION.PPThis paper describes how to writeprograms that interface with the.UC UNIXoperating 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 signalsduring execution..PPThe document collects material which is scatteredthroughout several sections of.IThe.UC UNIXProgrammer'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 languageroughly up to the level of.IThe C Programming Language.R[2].Some of the material in sections 2 through 4is based ontopics covered more carefully there.You should also be familiar with.UC UNIXitselfat leastto the level of.I.UC UNIXfor Beginners.R[3].