Systems & Operating Systems

Transcription

1 McGill University COMP-206 Sftware Systems Due: Octber 1, 2011 n WEB CT at 23:55 (tw late days, -5% each day) Systems & Operating Systems Graphical user interfaces have advanced enugh t permit sftware develpers (and ther users) t carry ut all basic file management peratins, like making directries, cpying files, etc. Graphical user interfaces have still nt been able t capture the file management's scripting ability. GUIs als have nt prvided a simpler methd by which a user can mdulate cmmands thrugh switches. Since yu are a new sftware develper it is the gal f this curse t give yu the basic skills that sftware develpers emply. This includes being cmfrtable arund a cmmand-line prmpt, creating perating system scripts, prperly managing a sftware prject and understanding the cncept f a system. This assignment will get yu t slve prblems in these areas. Questin 1: Sftware Systems 1.1 In the curse textbk, chapter 1, there is a discussin abut the getchar assembler prgram. Hw des that stry demnstrate the cncepts behind sftware systems? 1.2 Describe the relatinship an applicatin prgram has with the physical hardware f yur cmputer in terms f the sftware system layers that exists between them. As a case in pint, describe hw a string printed frm an applicatin exists the cmputer thrugh the netwrk card. Be nly as detailed as we have been in class, slides and the textbk, fcusing nly n the layers and transfrmatins the data string experiences identifying/assciating the changes t which layers/sftware subsystems. Questin 2: The Unix Operating System Cmmand Line When cnstructing a sftware prject the Sftware Develper's first task is t create space n the hard disk where the prject will be develped. T d this, a develper nrmally creates a series f directries. Sftware develpers try t rganize and manage their sftware prjects using many different techniques. One such technique is the directry/flder structure. Using the Unix cmmand line build the fllwing directry structure: Within yur hme directry create a directry called PUBLIC_HTML and COMP206. These directry names shuld be in lwer case. Directry PUBLIC_HTML will cntain yur web site. Directry COMP206 will cntain jvybihal Page 1 9/17/2011

2 yur curse files. I am writing these names in upper case t be clear in this dcument. On Linux yu shuld be naming these directries in lwer case. Within cmp206 create the directry PROJECT. Within PROJECT create the directries: ARCHIVE, BACKUP, BUILD, and DATA. As the curse prgresses we will create a web applicatin and place the prgrams fr that applicatin in the BUILD directry. Our database will be lcated in the DATA directry. This directry space is cnsidered t be part f ur develpment envirnment. Later, we will have t put this n the web (fr real) and this will be dne in ur deplyment envirnment, which is the PUBLIC_HTML directry (but that will cme later). The next thing we need t d is t create a database. Since this is nt a database curse and since many f yu have prbably nt prgrammed databases, ur database will be a "flat-file" database (i.e. a text file). Yu MUST use VI t create ur primary database (there will be mre databases later): Our database is called MEMBERS.CSV. It will cntain the fllwing infrmatin: User ID, user passwrd, full user name, security level (1 = supervisr, 0 = regular user), and purchase histry (dllar amunt sum). The member database cntains the names f all the valid users f yur applicatin (like in gmail). Fr this questin just supply 3 users, an example is shwn belw. A flat-file database (als called a CSV file, r cmma-separated vectr) is rganized arund recrds and fields. A field is each piece r type f infrmatin: like user ID r user passwrd. A recrd is a grup r set f fields. It cntains all the infrmatin abut a single user r prduct saved in yur database. In a flat-file, the recrd is ne line and cmmas separate fields. Fr example, the member's database culd lk smething like this: 1234, abcd, Jseph Vybihal, 1, , ddee, Bill Smith, 0, , ABCdef, Sam Smiley, 0, 100 Each rw cntains all the infrmatin abut ne user. This is called a recrd. A cmma separates each piece f infrmatin abut the user in that rw: ID first, then passwrd, fllwed by user name, etc. Pressing the carriage return terminates the recrd. There is als a carriage return n the last recrd. This leaves us with a blank line at the end f the file. This is kay. Nte that nthing is encrypted (at this time at least). Fr questin 1 d: Create the develpment envirnment directry structure (recrd yur cmmandline cmmands in a text file called STRUCT.TXT. Yu culd use the recrding cmmand t autmatically recrd what yu d int that file.). I cannt cnfirm if yu actually created the directry structure using the cmmand-line. Yu culd jvybihal Page 2 9/17/2011

3 have dne it using Windws and then pretended. T vercme this, I am asking yu t type ut the cmmands yu wuld use, in-rder within this text file, as if yu where at the cmmand-line actually ding it (Yu shuld ACTUALLY d it but the TA will nt verify this, nly the STRUCT.TXT file yu uplad t WEB CT). Yu can use the Unix cmmand-line cmmand called Script, as we saw in class, t autmatically recrd yur cmmand-line inputs. Using VI, create the databases MEMBERS.CSV (this name can be in lwer case) and ppulate with data (build and save them in the directry DATA). Then send these text files t WEB CT. Again I cannt cnfirm if yu actually used VI but I suggest yu d, s that yu can be used t it fr exam questins. Questin 3: Lg-in Shell Scripts An perating system's scripting envirnment is a prgramming language fr the shell. These files are nt cmpiled. The shell interprets them. But they give the prgrammer an avenue where they can autmate perating system prcedures since all cmmand-line cmmands can be part f the script prgram. In additin they als prvide a rudimentary cntrl flw language that actually permits yu t d sme real prgramming (in the real sense f the technlgy). Tw frms f scripts exist in Unix: the set-up (r lg-in) script, and the batch (r OS) script. There are many OS scripting languages. One f the mst cmmn frms f script prgramming in Unix is knwn as BASH. Yu shuld develp yur scripts in this language. This questin asks yu t explre set-up scripts. Set-up scripts are used t initialize r cleanup the shell envirnment when yu lg-in r lg-ut. Shells are initiated and destryed when yu lg-in and ut f the perating system. Yu are als permitted t switch shells at any time. Yu have the pprtunity t select the shell yu want t use and thrugh its setup script yu can custmize it's lk and feel, and then clean up yur sessin when yu lg-ut (if yu need t). This assignment questin wants yu t custmize yur current Unix lg-in set-up script. As discussed in class there are a few lg-in script files in Unix depending n the default shell the cmputer uses. Identify the default shell that is in peratin during yur lg-in and mdify its lg-in script in the fllwing ways: Custmize the prmpt. Display the cntents f the directry yu have been sent t Display the date and time List all the users currently lgged n jvybihal Page 3 9/17/2011

4 Finger ne f yur friends Alias the ls -l -a cmmand t the wrd lsa, and Launch yur web brwser applicatin (this will nly wrk n campus). Yur lg-in script can prcess this in any rder yu like. Try t make the utput pretty. Questin 4: Batch Prcessing Batch prcessing is a special use f scripts fr managing and autmating the executin f applicatins. Histrically they were created fr large mainframe cmputers that culd nly execute ne prgram at a time. Setting up a mainframe t execute a user's applicatin tk a lt f time. Therefre there was a lt f wasted time (and mney) between executins. Nrmally a "Jb" wuld run fr 0.5 secnds and the set-up time was 10 t 20 minutes. This was nt cst effective. The slutin was t have a special script that in the mrning wuld be built cntaining the instructins n hw t initialize the runtime envirnment, run the applicatin and perfrm any cleanup f files and allcated resurces fr each Jb. Then the mainframe wuld fly thrugh all these applicatins setting up the executin envirnment, printing the results and setting up fr the next Jb, until all were dne. BASH is the mdern batch prgramming envirnment. These days, we view a Jb as the tasks the user wants the cmputer t prcess autmatically. The user then waits fr the wrk t cmplete and verifies the results. Bash files are created as needed by the user, nt nce at the beginning f the day. Let us try a simple versin f this. Prgrammers lve t make backups because, as a rule, smething will g wrng and it is always gd t be able t g back t a previus versin that yu are sure is still kay. Inside the SOURCE directry create a bash file called BACKUP (this name shuld be in lwercase). Remember t use CHMOD t make it executable. BACKUP will use ne input parameter, the syntax is described belw: BACKUP files Where: Files: is either the name f a single file (like bb.txt r *.txt r bb.*) r it is a list f file names separated by spaces (like bb.txt mary.txt jn.txt). These are the files that will be backed up int the BACKUP directry. Yu can assume that the script will always be called frm the SOURCE directry. If n file names are prvided then the entire cntents f the SOURCE directry will be cpied int the BACKUP directry. Nte that this des nt zip the files. It nly cpies the requested files frm the SOURCE directry t the BACKUP directry. The script itself shuld nt be in the BACKUP directry. jvybihal Page 4 9/17/2011

5 WHAT TO HAND IN Everything must be submitted t WEB CT befre the due date. Remember that WEB CT permits yu t hand in up t tw days late but there will be a penalty f 5% each day. After that, the WEB CT submissin bx will clse. Please hand in the fllwing: Fr questin 1: A text, wrd r PDF file named A1Q1 with the answer. Fr questin 2: STRUCT.TXT, and MEMBERS.TXT. Please remember that STRUCT.TXT cntains the cmmand-line sessin yu used t create the requested directry structure. Include ALL the Unix cmmands yu used, inthe crrect rder. Fr questin 1: The lg-in file yu edited. Fr questin 4: The script named BACKUP. HOW IT WILL BE GRADED The TA will use the fllwing instructins when grading yur assignment. TA's are ften given additinal instructins nt presented here but cmpiled frm cmmn student questins r fund prblems in the assignment r adjustments t the assignment prcedures. ASSIGNMENT: is wrth a ttal f 20 pints. Questin 1: is wrth 5 pints +2.5 fr fr 1.2 QUESTION 1: is wrth 5 pints. +3 STRUCT.TXT, prprtinal t the number f crrect cmmands presented +2 Prper structure f flat file QUESTION 2: is wrth 5 pints. Graded prprtinally. QUESTION 3: is wrth 5 pints. Graded prprtinally jvybihal Page 5 9/17/2011

6 GRADING RULES The fllwing rules are fllwed by the TA when grading assignments: A prgram must run in rder t get a grade (even if it des nt run well). If it des nt run (des nt cmpile) it will receive a zer. (Make sure t run yur prgrams frm Trttier they smetimes d nt run the same frm hme when lgging in using putty since mimi is nt the same server as the ne yu use in schl.) All questins are graded prprtinally (assuming the prgram runs at all). This means that if 40% f the questin is crrect, yu will receive 40% f the grade. jvybihal Page 6 9/17/2011