.NHScripts..PPAs mentioned above, the present scripts tryat mostto follow a three-track theory.  Thus littleof the potential complexity of the possible directed graphis employed, sincecare must be taken in lesson construction to seethat every necessary fact is presented inevery possible path through the units.  In addition,it is desirable that every unit have alternate successorsto deal with student errors..PPIn most existing courses, the first few lessonsare devoted to checking prerequisites.  For example,before the student is allowed to proceed through the editorscript the script verifies that the student understands filesand is able to type.It is felt that the sooner lack of student preparationis detected, the easier it will be on the student.Anyone proceeding through the scriptsshould be getting mostly correct answers; otherwise, thesystem will be unsatisfactory both because the wronghabits are being learned and because thescripts make little effort to deal with wrong answers.Unprepared students should not be encouragedto continue with scripts..PPThere are some preliminary items which the student mustknow before any scripts can be tried.  In particular,the student must know how to connect toa.UXsystem,set the terminal properly,log in,and execute simple commands (e.g.,.ullearnitself).In addition, the character erase and line kill conventions(# and @) should be known.It is hard to see how this much could be taught bycomputer-aided instruction, since a student whodoes not know these basic skills will not be ableto run the learning program.A brief description on paper is provided (see Appendix A), althoughassistance will be needed for the first fewminutes.  This assistance, however, need not be highly skilled..PPThe first script in the current set deals with files.  It assumesthe basic knowledge above and teaches the student aboutthe.I ls ,.I cat ,.I mv ,.I rm ,.I cpand.I diffcommands..tr ~It also deals with the abbreviation characters *, ?, and [\ ]in file names.It does not cover pipes or I/O redirection,nor does it present the many optionson the.ullscommand..PPThis script contains 31 lessonsin the fast track;two areintended as prerequisite checks,seven are review exercises.There are a total of 75 lessons in all three tracks,and the instructional passages typed at the studentto begin each lesson total 4,476 words.  The averagelesson thus begins with a 60-word message.In general, the fast track lessons have somewhat longerintroductions, and the slow tracks somewhat shorter ones.The longest message is 144 words and the shortest 14..PPThe second script trains students in the useof the.UXcontext editor.I ed ,a sophisticated editorusing regular expressions for searching..[ritchie thompson unix  seventh edition 1978%O See section \f2ed\f1 (I)..]All editorfeatures except encryption, mark names and `;' in addressingare covered.The fast track contains 2 prerequisite checks,93 lessons, and a review lesson.It is supplemented by 146 additional lessons in other tracks..PPA comparison of sizes may be of interest.  The.uleddescriptionin the reference manual is 2,572 words long.  The.uledtutorial.[kernighan editor tutorial 1974.]is 6,138 words long.  The fast track throughthe.uledscript is 7,407 words of explanatory messages, and thetotal.uledscript, 242 lessons, has 15,615 words.The average.uledlesson is thus also about 60 words; the largestis 171 words and the smallest 10.Theoriginal.uledscript represents about three man-weeks of effort..PPThe advanced file handling script deals with.ullsoptions,I/O diversion, pipes, and supporting programs like.I pr ,.I wc ,.I tail ,.I spelland.I grep .(The basic file handling script is a prerequisite.)It is not as refined as the first two scripts;this is reflected at least partly in the fact thatit provides much less of a full three-track sequencethan they do.On the other hand,since it is perceived as ``advanced,''it is hoped that the student will have somewhatmore sophisticationand be better able to cope with it at a reasonablyhigh level of performance..PPA fourth script covers the.uleqnlanguage for typing mathematics.This script must be run on a terminal capable of printingmathematics, for instance the DASI 300 and similar Diablo-basedterminals, or the nearly extinct Model 37 teletype.Again, this script is relatively short of tracks:of 76 lessons, only 17 are in the second track and 2in the third track.Most of these provide additional practice for studentswho are having trouble in the first track..PPThe.I \-msscript for formatting macrosis a short one-track only script.The macro package it describes is no longer the standard,so this script will undoubtedly be supersededin the future.Furthermore, the linear style of a single learn script is somewhatinappropriate for the macros, since the macro package is composed of manyindependent features, and few users need all of them.It would be better to have a selection of short lessonsequences dealing with the features independently..PPThe script on C is in a state of transition.It was originally designed to followa tutorial on C,but that document has since become obsolete.The current script has been partially convertedto follow the order of presentation in.ulThe C Programming Language,.[ritchie kernighan programming 1978 prentice hall.]but this job is not complete.The C script was never intended to teach C;rather it is supposed to be a series of exercisesfor which the computer provides checking and(upon success) a suggested solution..PPThis combination of scripts covers much of the material which any.UXuserwill need to knowto make effective use of the system.With enlargement of the advanced filescourse to include more on the command interpreter, therewill be a relatively complete introduction to.UXavailable via.ullearn.Although we make no pretense that .ullearnwill replace other instructional materials,it should provide a useful supplement to existing tutorials and reference manuals.