Orientation. CS133 Reflections. Knowledge you may need. Experience of computers METAPHORS. Know UNIX like knowing London

Size: px

Start display at page:

Download "Orientation. CS133 Reflections. Knowledge you may need. Experience of computers METAPHORS. Know UNIX like knowing London"

Carmella Miles
5 years ago
Views:

1 Orientation CS133 Reflections experience and logic scruffy and neat cf. PowerPoint background and slide content computer + peripherals and program Meurig Beynon symbols have to mean something what shell commands mean is hard to say metaphor is very significant, so are models Experience of computers Knowledge you may need enable things, play music, download from web somewhere familiar, expressive, put you in control, embody reason get in the way of things, impose on our-selves frustrating to use, create artificial constraints alienating, beyond total understanding names of machines type of shell that they run why set in csh isn t the same as set in bash how to get into computer utilities and especially how to get out of them knowledge that you get from experience Know UNIX like knowing London METAPHORS What s down that street? How do I get to X? However well you know London, answer may be I DON T KNOW consult the A to Z ask somebody explore consult the manual ask somebody play with the system Like London is a metaphor we use many other metaphors 1

2 Metaphor for a UNIX operating system About metaphors Metaphor for a computer Not all metaphors give much insight, but you need to devise metaphors to understand e.g. one process PIPES its output to another must be cautious about abusing metaphor: these computers are engaging in intelligent discussion about their emotional states Metaphor for a file system MODELS M serves as a model for R if there are counterparts in M for what you find in R by way of things you can observe and change there is a reliable correspondence between what you can observe through experimenting with R and what happens when you make similar observations and experiments in M Metaphor for a UNIX operating system (HELPFUL, BUT RATHER LIMITED) Metaphor for a computer (QUITE GOOD IN 1964) Metaphor for a file system (A STRONG METAPHOR) A model of the file system File system as planetary system Check out the xcruiser application at website: xcruiser.sourceforge.net/demo.html How well do directories and files correspond to galaxies, stars and planets.? Can interpret commands: ls, rm, rmdir, cd, mv, chmod, and concepts such as current (.) and parent (..) directory Do you find this explanatory? or ex-planetary? 2

A scruffy model of the vi editor About the vi model Background colour for the highlighted character encodes the current mode NORMAL / VISUAL ( vi ) MODE INSERT MODE Limited functionality enough to

3 A scruffy model of the vi editor About the vi model Background colour for the highlighted character encodes the current mode NORMAL / VISUAL ( vi ) MODE INSERT MODE Limited functionality enough to illustrate modes Complexity of the interface reflecting history of vi Model is incomplete : yet to be done dealing with write, quit, delete and insert lines adding button for replace in normal mode handling input other than lower case characters LINE EDITING ( ex ) MODE Contrast with manual entry and vimtutor More about the vi model To find out more about the model of the vi editor, check out the Empirical Modelling archive: The model is available as vimodesbeynon2006 Appreciating different viewpoints e.g. different perspectives on the ECDL the ECDL is of little personal interest to you as a professional IT person, you need to know about issues like the ECDL as a student of computer science, how do you think word-processors, spreadsheets and databases relate to computing as a whole? Open Office Tools OpenOffice.org is a free office suite application available for many different operating systems including Microsoft Windows, Linux, Solaris and Mac OS X. It is intended to be a compatible alternative to Microsoft Office. It supports the OpenDocument standard for data interchange. Wikipedia 3

4 Open document format The Open Document Format for Office Applications [OpenDocument or ODF] is an open format for saving and exchanging office documents such as memos, reports, books, spreadsheets, databases, charts, and presentations. This standard was developed by the OASIS industry consortium and based upon the XML format originally created by OpenOffice.org. Motivations for Open Source Need to be critical about the status of commercially successful products. For instance: Is PowerPoint really a good presentation tool?! Do I/we really think in terms of little groups of words that fit onto a slide, have a certain colour and layout, and are naturally suited to being presented under a banner saying what this is slide is about? No! I don t, but here goes Proprietary formats don t assist understanding... Here s the same html as processed by MS word and presented using PowerPoint Consider html files. Here s some simple html: <html>  <h1>cs133 Term 1 Example Sheet 1</h1>   <ol> <li> <p>the file <code>/usr/../bin/././../././bin</code> has a shorter name. What is it? </p>. <html xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns=" <head> <meta http-equiv=content-type content="text/html; charset=us-ascii"> <meta name=progid content=word.document> <meta name=generator content="microsoft Word 11"> <meta name=originator content="microsoft Word 11"> <link rel=file-list href="ex1msword_files/filelist.xml"> <title>cs133 Term 1 Example Sheet 1</title>  <style>  </style>  </head> <body lang=en-gb link=blue vlink=blue style='tab-interval:36.0pt'> <div class=section1> <h1>cs133 Term 1 Example Sheet 1<o:p></o:p></h1> <p style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1; tab-stops:list 36.0pt'><![if!supportLists]><span style='mso-list:ignore'>1.<span style='font:7.0pt "Times New Roman"'> </span></span><![endif]>The file <code><span style='font-size:10.0pt'>/usr/../bin/././../././bin</span></code> has a shorter name. What is it? </p> Google spreadsheet supports the ODS file format This should ideally mean (for instance) that a Google spreadsheet can be roundtripped : saved in ODS format, read by OpenOffice, saved again in ODS format re-read by Google spreadsheet without any information loss 4

5 Steve Zaske s blog... I tested Google s ODS support by roundtripping a simple spreadsheet through Google Spreadsheet. And what did Google Spreadsheet do? It: 1. Deleted my charts 2. Removed the conditional formatting 3. Deleted file versions information & data I added 4. Deleted my document properties 5. Removed the new styles I added and the one formula I added into my spreadsheet broke because Google Spreadsheet supports the Round() function differently than OpenOffice. [12 th Sept 2006] Who is Steve Zaske? from the About page accompanying his blog: I work at Microsoft working on the next version of Microsoft Office, but everything here is my own personal opinion. Comment from Andrew Yeomans OpenDocument format *is* a standard. Some implementations have deficiencies. But that s not a reason to criticise the *format* standard. I might just as unfairly criticise the new Microsoft Office XML format because of its poor support in Office 2003, Google Writely/Spreadsheet and OpenOffice.org. Who is Andrew Yeomans? Andrew Yeomans is Vice President of Global IT Security at Dresdner Kleinwort Wasserstein investment bank. Prior to that, Andrew was IBM s European technical specialist in firewalls and Internet security. He is co-author of Java Network Security, the first book to cover secure multi-tier Java applications. He has worked with UNIX and Open Source software since 1985, and managed and ran IBM s Scientific and Technical Computing group s UNIX network. Speaker Bio associated with Presentation Is Open Source now Microsoft's biggest enemy? Or a hotbed of unconstitutional fundamentalists out to destroy life as we know IT? It's a fact that Open Source / Free Software and Linux had more mainstream news headlines in the first half of 2004 than in all of 2003, with promises ranging from significantly lowering your IT costs through to binding you into expensive legislation Morals Look critically at all the advice you get Don t believe everything you find on the web Question the things we tell you Try to check the credentials of all informants Read several views and look for coherence Make up your own mind about things Everybody s different - find what suits you 5

6 SSH WITH PUTTY 1 1. ENTER joshua.dcs.warwick.ac.uk HERE 2. SPECIFY PORT HERE e.g SPECIFY SECURE SHELL HERE e.g NAME YOUR SESSION HERE e.g. joshua 5. PRESS Save SESSION NAME APPEARS HERE SSH WITH PUTTY 2 joshua.dcs.warwick.ac.uk APPEARS HERE CHECK PORT HERE e.g. 22 SESSION NAME APPEARS HERE e.g. joshua 3. PRESS Open 2. PRESS Load 1. SELECT SESSION NAME HERE Computer as a data processor family of concurrently acting processes process has input and output streams cf. cable carrying electricity from plug to laptop redirection of IO like using another plug / using the same cable for something else processes spawned dependent / independent me riding my bike to the shops me sending my wife to the shops Ownership and Control processes are owned by different agents can t stop it raining can go driving the car processes are controlled by different agents my wife sending me to shop my wife sending the man next door to shop and so access variables differently who sees what s in the shop today? 6

Sequential and concurrent processes combine sequentially to make jobs having meal = shopping, cooking, eating processes combine concurrently to make jobs having takeaway meal ordering laying the

want lightweight programming, things that work close to the machine lots of little processes should be flexible BUT difficult to define them precisely because the computer + peripherals are

7 Sequential and concurrent processes combine sequentially to make jobs having meal = shopping, cooking, eating processes combine concurrently to make jobs having takeaway meal ordering laying the table :: cooking the meal collecting the meal :: preparing extra rice eating the meal Human and machine viewpoints Why the process metaphor? want lightweight programming, things that work close to the machine lots of little processes should be flexible BUT difficult to define them precisely because the computer + peripherals are physically so rich difficult to relate to our big abstract intentions tension between neat and scruffy programming Other machine models The Turing Machine model (1936) Machine models of a computer always have means to store data objects in Java, files and variables in UNIX means to manipulate data methods in Java, processes in UNIX ways to program data manipulation JAVA programs, UNIX shell scripts store is represented by an unbounded tape processor is represented by a read/write head program is represented by a set of rules Suzanne Skinner (1996) Java applet simulator at: A Turing computation in progress recognising a palindromic string A Turing computation in the halt state rejecting a non-palindromic string 7

8 The Church-Turing thesis There is no computational model that is in principle more powerful than the Turing machine all algorithmic data processing is equivalent to Turing computation by this criterion, the UNIX shell is a full programming language Why use UNIX programming? UNIX programming for system maintenance greater day-to-day efficiency in file management and processing, and in program development usefulness of casual programming bash$ cat >myalarm bash$ sleep 120 bash$ echo Time to wake up bash$ type control-d bash$ myalarm& Note on slide 4.3 A script is a sequence of statements which can take arguments The primary ingredient in a script is the command A command takes the form of an operator followed by a list of arguments: operator sequence of arguments Note on slide #!/usr/bin/perl -n BEGIN{$num_ahead=0; $num_left=0; $num_right=0; $num_behind=0;} $num_ahead++ if/^i'm going forward/; $num_left++ if/^i'm going left/; $num_right++ if/^i'm going right/; $num_behind++ if/^i'm going backwards/; print"summary of moves: Forward=$num_ahead Left=$num_left Right=$num_right Backwards=$num_behind\n"; Comments on slides 4.6 and 4.10 Note the importance of the fact that all variables have values of type string slide 6 Exercise (slide 10): type commands such as bash$ echo hello > hello bash$ echo hello > hello bash$ echo hello > hello etc. and note how they all have the same result Further note on slide 4.10 Because all variables have values of type string the way in which the shell interprets strings is very loose, flexible and dependent on the context e.g. - where a command is expected it tries to interpret the given string as being of the form: operator sequence of arguments - where a filename is expected (e.g. after a > symbol in a string) it tries to locate a file 8

9 Comments on slide 4.11 Construct a script with the contents: case $X in hello) echo "Hello there!" ;; *) echo "pardon?" ;; esac and consider the issues arising from the fact that the variable $X is local the way in which $X is defined / initialised Comments on slide 4.18 To obtain the same result with backquotes: bash$ X = `date; date` bash$ echo $X Note the many different styles of quotation mark: cf. singlequote ( ) and doublequote ( ) on slide 10. Comments on slide 4.19 Examples using test include : bash$ test e filename # success if file exists bash$ echo $? # tests exit status exit status is 0 if test succeeds, else 1 bash$ X=hello; Y=abc bash$ test $X = $Y && echo X and Y are equal note the space around = in this conditional and the interpretation of the && list command Useful additional commands Two commands that are useful in managing and reviewing an interactive session: history retrieves the list of previous commands history > savedsessionhistory fc l gives access to recent commands for edit (with vi) and re-execution Interpretations of strings Young lady to elderly gentleman in theatre: are you 25? (meaning seat number) Reply: I wish I was (meaning age) Girl exiting bar, passing boy entering: I m FURIOUS I m Clive pleased to meet you Frail old man passing cemetery with KEEP OUT notice: What do you think I m trying to do? Types of knowledge Being able to program the shell needs different kinds of knowledge, analogous to knowing: that you need to know a plumber a plumber how a plumber does what she does how to do what a plumber does yourself Good to be able to identify your problem this way 9

10 E.g. ops on files Joy of Unix p74 file head tail diff cmp uniq cut paste fold sort + relevant options of these & more familiar ops e.g. bash$ ls t1 head n 1 UNIX philosophy Supply lots of small utilities, use in combination List the most recently accessed file: bash$ ls t1 head n 1 ls t most recently accessed first ls -1 one filename per line head n 1 select first item from file UNIX philosophy in action Supply lots of small utilities, use in combination Find out how deeply nested a directory is: bash$ echo $PWD tr / wc -w echo $PWD print name of current directory tr / substitute spaces for slashes wc -w count number of strings in list Miscellaneous points Useful things to remember when using Linux: command line completion (pressing the Tab key) is a way of reading the systems expectations there is a history of commands entered that can be useful for documenting a session the online manual pages are easier to search and access via links the Joy, Luck, Jarvis book is online via webpage Revising lecture material Lecture notes are often long and linear in form Need to be able to revise them quickly Good to index and condense them into notes Make a point of noting what you do and don t know Understanding is the art of making connections 10

11 Notes on Lecture 7 (1) Main theme of the lecture notes: Utilities that can be used as filters grep, tr and sed (see slide 20) Slides 1-20 deal with grep and tr Slides deal with sed Slide note on other editors and books Notes are entitled Regular Expressions, which is the main new underlying concept Notes on Lecture 7 (2) Regular expressions [2, 5, 6-17] - two kinds of regular expression [2, 5] - basic r.e [BRE] and extended r.e [ERE] - syntax for BREs and EREs ( shell REs) [7,16] - compared [16]: each has features other doesn t - BREs backreferences - EREs alternation - BREs use $, \{ etc where EREs use (, { etc Notes on Lecture 7 (3) The grep filter: Get regular expression patterns? - introductory slides [3,4] - uses r.e. s of both basic and extended kinds [6] - grep (BREs), egrep (EREs), fgrep (literal) [6] - egrep = grep E and fgrep = grep F [6] - illustrative examples of grep on BREs [8-15] The tr filter: translator - definition, examples, delete (-d) option [18,19] Notes on Lecture 7 (4) Summary of RE syntax and semantics ^, $ start, end of line. single character [abc], [^abc] one of, not one of [a-c] range \( $, () subexpression (BRE, ERE) * repetition \{ \}, {} interval expressions (BRE, ERE) Notes on Lecture 7 (5) Notes on Lecture 7 (6) Distinctive BRE, ERE syntax & semantics available in BRE only \n backreference [11] (NB \n isn t newline, but \1, \2 etc) available in ERE only alternation [17] The stream editor (sed) [20-39] sed and e, -f options [20] form of sed scripts [21] - address function [argument] how sed works [22] comments [23], addresses [24], functions [25] illustrating simple functions on test data [26-32] advanced features: files [33], Hold Space [34-5] substitution with illustrative examples [36-38] 11

12 Notes on Lecture 7 (7) How sed works [22] need a simple model of this: input stream pattern space output stream stream here means stream of lines by default, input is passed to output line-by-line unchanged sed acts on the lines it recognises as they pass can copy them into the output (to duplicate) can delete them, can transform them Notes on Lecture 7 (8) sed input stream pattern space output stream sed acts on the lines it recognises as they pass uses an address to check against each line [21] can copy them into the output (to duplicate) can delete them, can transform them performs a simple function on each line [21] Notes on Lecture 7 (9) Summary of simple sed functions [25] d delete (not on [25]!) illustrated [27,28] p print from pattern space to output [29] q halt the stream editing process [30] = introduce line numbers [31] s substitute for BREs in lines [36-38] Illustration of the use of Hold Space not too easy What is the -f option? Check out d example [28] Varieties of programming Shell programming vs Java programming? part of a bigger picture of so-called programming paradigms - procedural explicit model of state, assignment of values - declarative implicit model of state, declaration of values Procedural paradigms Turing machine - explicit state is tape - assignment by writing symbols to the tape Java programming - explicit state is object attributes - assignment by methods of the object Shell scripting - explicit state in environmental variables / files - assignment to variables and action of utilities 12

13 Uses for different models Turing machine - a theoretical model for algorithms - basis of theories of solvability and feasibility Java programming - practical software development - especially oriented towards web programming Shell scripting - basis for LINUX systems programming - applied in HumDrum musical analysis tools Object-oriented programming programming as modelling Simula (Birtwistle et al, 1967): programs can be written by modelling the world in objects object = set of attributes with integrity and identity together with characteristic operations (methods) OO thesis: We conceptualise the world this way OOP based on OO modelling Promising for certain kinds of systems Problematic aspects: OO modelling doesn t always seem to smoothly blend with OO programming OO modelling has been subverted for modularisation and distribution in software development (quoting Graham Birtwistle) Event-driven programming Program by specifying stimulus-response patterns: when event x occurs carry out action y triggers for actions e.g. when the value of variable x changes, update its on-screen value when the switch is closed, put the light on when the temperature reaches boiling point, sound the alarm favoured by agent-based / rule-based systems Problems of procedural models Challenges in procedural programming managing and interpreting state intermediate states are not meaningful complex interactions between rules explicit specification of all action possible remedies: use of assertions and constraints automatic management of dependencies Declarative paradigms functional programming e.g. SML, Miranda - every program is conceived as a function - maps input (possibly a stream) to output - uses a rich and powerful function evaluator logic programming e.g. Prolog - every program is conceived as a predicate - maps specified values to unknown values - uses a rich and powerful inference engine 13

14 Functional programming (FP) Interpreting the primes program A functional program to compute prime numbers: factors n = [r r<-[1..n div 2]; n mod r = 0] isprime q = (# factors q) = 1 functional based on specifying functions The functions in this context are factors() and isprime() factors n = [r r<-[1..n div 2]; n mod r = 0] isprime q = (# factors q) = 1 factors(n) = the set of numbers between 1 and n/2 that leave remainder zero when divided into n hence factors(6) is [1,2,3], factors(7) is [1] isprime(q) = true if factors(q) is a list of length 1, otherwise false FPs as specifications factors n = [r r<-[1..n div 2]; n mod r = 0] isprime q = (# factors q) = 1 func factors { ## derived from the functional program para n; auto i, result; result=[]; for (i=1; i<=n/2; i++) if (n == (n/i)*i) result = result // [i]; return result; } Logic programming primes(1) <=> true. primes(n) <=> N>1 M is N-1, prime(n), primes(m). % generate candidates prime(i) \ prime(j) <=> J mod I =:= 0 true. The constraint primes(n) generates candidates for prime numbers, prime(m), between 1 and N. The candidates react with each other such that each number absorbs multiples of itself. In the end, only prime numbers remain. [SICStus Prolog] Programming with dependency factors_n is factors(n); isprime_n is factors_n#==1; text_on_display is The number is // str(n) // (isprime_n)? : not // prime ; introduce a way to specify screen state by dependency and express this by definitions Empirical Modelling Empirical Modelling is a methodology for modelling with dependency based on observation-oriented principles where primary concepts are observables, dependencies, agents: Sample models in the Empirical Modelling archive: For the vi model, see vimodesbeynon

15 Extending vimodesbeynon2006 (1) Illustrating Empirical Modelling blending primality testing with the vi model Load the vimodesbeynon2006 model, then carry out the extensions that follow %eden func factors { para n; auto i, result; result=[]; for (i=1; i<=sqrt(n); i++) ## better than i<=n/2 if (n == (n/i)*i) result = result // [i]; return result; } Extending vimodesbeynon2006 (2) ## testing the function factors() writeln(factors(6)); writeln(factors(7)); ## using factors() in a script N=127; factors_n is factors(n); isprime_n is factors_n#==1;?isprime_n; Extending vimodesbeynon2006 (3) N is int(char(currchar)); ## set N to ASCII current char %scout string bgcoldocwin; window docwin = { type: TEXT frame: ([{0, 0}, {(maxlen + 1).c, 4.r}]) string: textediting bgcolor: bgcoldocwin fgcolor: "black" border: 1 }; %eden ## make background of vi window depend on N bgcoldocwin is (isprime_n)? "lightblue" : "white"; Extending vimodesbeynon2006 (4) line4 = "aaaaaaaaaaaaaaaaaaa"; line1 is line4; func stringtobin { para s; auto i, result; result = ""; for (i=1; i<=s#; i++) result = result // str(int(char(s[i])+4)%2); return result; } Extending vimodesbeynon2006 (5) ## change the first line into a number textediting is mark1 // newline1 // "\n" // mark2 // line2 // "\n" // mark3 // line3 // "\n" // mark4 // line4 // "\n"; ## make the first line of the vi text depend on line1 ## note that line1 is defined to be line4 ## stringtobin() maps chars to 0/1 (see slide 87) newline1 is stringtobin(line1); 15

16 Extending vimodesbeynon2006 (6) ## convert a binary string into an integer: func binstrtoint { para s; auto i, result; result = 0; for (i=1; i<=s#; i++) result = result * 2 + (s[i]-48); return result; } Extending vimodesbeynon2006 (7) ## determine whether the binary number in line 1 ## is a prime or not and display the result: factors_m is factors(m); isprime_m is factors_m#==1; M is binstrtoint(newline1); ansstr is (isprime_m)? "" : "n't" ; line2 is "The number " // str(m) // " is" // ansstr // " prime"; line3 is "It has " // str(line1#) // " binary digits"; Extending vimodesbeynon2006 (8) You can experiment with redefining various things and check out the effects as you extend the model. After the above extensions have been made, an obvious way to use the model is to apply vi to the string line4 - or assign to it, as in line4 = Meurig ; - and see what effect this has on the primality of the associated binary number in line1. The string of a s currently in line4 gives a potential Mersenne prime. 16

Table of contents. Our goal. Notes. Notes. Notes. Summer June 29, Our goal is to see how we can use Unix as a tool for developing programs

Table of contents. Our goal. Notes. Notes. Notes. Summer June 29, Our goal is to see how we can use Unix as a tool for developing programs Summer 2010 Department of Computer Science and Engineering York University Toronto June 29, 2010 1 / 36 Table of contents 1 2 3 4 2 / 36 Our goal Our goal is to see how we can use Unix as a tool for developing