Week Four Agenda

2. Week Four Agenda • Announcements • Link of the week • Review week three lab assignment • This week’s expected outcomes • Next lab assignment • Break-out problems • Upcoming deadlines • Lab assistance, questions and answers

3. Link of the Week Object Code • http://freedom-to-tinker.com/blog/felten/source-code-and-object-code • What is object code? • Object File Format • What is Executable and Linking Format?

4. Link of the Week

5. Link of the Week

6. Review Week Three Lab Assignment Script Comments Scripts should contain comments to help the user understand what the script is doing or not doing. The functionality comments should be detailed enough to give the user a good overall understanding about the script. Execution contingencies: Script functionality: Script limitations: Input data:

7. Review Week Three Lab Assignment A process associates a number with each file that it has opened. This number is called a file descriptor. When you log in, your first process has the following three open files connected to your terminal. Standard Input (stdin) : Filedescriptor 0 is open for reading. < really means <0 Standard Output (stdout): File descriptor 1 is open for writing. > really means 1> Standard Error (stderr): File descriptor 2 is open reading. >> really means 1>>

8. Review Week Three Lab Assignment Perl is a simple language that compiles and executes like a shell or batch type file. Perl doesn’t impose special growth limitations on an array or data strings Perl is a composite of C, AWK, and Basic. Perl was originally developed to manipulate text information.

9. Review Week Three Lab Assignment • Perl’s capabilities range from - System administration - Web development - Network programming - GUI development • Perl’s major features are • Procedural Programming makes use of simple sequential steps, routines, subroutines, and methods. • Object Oriented Programming (OOP) makes use of “objects”. The key elements of are inheritance, modularity, polymorphism, and encapsulation.

10. Review Week Three Lab Assignment Perl and Shell Similarities Perl scalar@ARGV ~ Shell $# Perl $ARGV[0] ~ Shell $1 Perl $ARGV[1] ~ Shell $2 Perl unless(scalar(@ARGV)==2) ~ Shell if [ $# != 2] All Perl statements are terminated with a “;” Perl exit 0 is returned if execution was successful. Perl exit 1 is returned if execution fails.

11. Review Week Three Lab Assignment Perl syntax $? - this variable contains the return value # - precedes a comment statement in Perl \n - new line syntax “ …” $strexp = “This text is considered as a string”; ‘ …’ $charexp = ‘a’; ` …` $cmdexp = `ls –l`; @ARGV – array containing command line arguments $_ - default implied scalar

12. Review Week Three Lab Assignment There are two types of relational operators. One class operates on numeric values, the other on string values. Relational operators NumericStringMeaning > gt Greater than >= ge Greater than or equal < lt Less than <= le Less than or equal

13. Review Week Three Lab Assignment Equality Operators NumericStringMeaning == eq Equal to != ne Not equal to  cmp Comparison, sign results -1 if the left operand is less 0 If both operands equal 1 If the left operand is greater

14. Review Week Three Lab Assignment Commands cal –y (display a calandar for the year) cal –j 2010 (display Julian dates) cal –m 2010 (display Monday first day) cal –s 2010 (display Sunday first day) cal 9 2010 (display September 2009 month)

15. Week Four Expected Outcomes Learning Outcomes • Write Perl scripts, including variables, control flow, and regular expression syntax

16. Next Lab Assignment • Perl is designed to - Process text data - Perform pattern matching (regular expressions) - Utilize string handling tasks • Perl is available on many platforms - UNIX - Linux - HP-UX

17. Next Lab Assignment Perl utilizes two types of categories - Singular variables that represent a single-value. The variable prefix symbol for a scalar is the $. Example: $scalar_variable_name - Plural variables are ones that contain multiple-values. Arrays and hashes are two multi-valued variables. Example: @array_variable_name Example: %hash_variable_name

18. Next Lab Assignment Perl data types $answer = 42; (an integer) $pi = 3.14159265; (a “real” number) $animal = “horse”; (string) $statement = “I exercise my $animal”; (string with interpolation) $amount = ‘It cost me $5.00’; (string without interpolation) $cwd = `pwd`; (string output from a command)

19. Next Lab Assignment Definition: An array is an ordered list of scalars, accessed by the scalar’s position in the list. @garage = (“car”, “mower”, “broom”); @persons = (“Will”, “Karim”, “Asma”, “Jay”); $count = @persons; Demonstrate Execute week_four.pl script

20. Next Lab Assignment Open Statement The open function can be used to create file handles for different purposes (input, output, piping), you need to be able to specify which behavior you want.

21. Next Lab Assignment open function # Input file open(file_handler, “file_name”) # Input file open(file_handler, “<file_name”) # Output file open (file_handler, “>file_name”) # Append file open (file_handler, “>>file_name”)

22. Next Lab Assignment Definition: Filehandleis utilized for both input and output files. Most file names are cryptic and are meaningless to programmers. The purpose of a filehandle is to help the programmer remember a simple file name throughout a program. A filehandle is a name given for a file, device, socket, or pipe. Filehandle command line format: open(filehandle, file name, permissions, chmod); Example: open($FH,$file_name);

23. Next Lab Assignment List Processing Example: @math_array= (6 - 4, 4 * 4, 8 / 2, 9 - 8); while ( … ) { … }

24. Next Lab Assignment For loop Example: for (counter = 0; counter < 10; counter++) { … } Three expressions are contained in a for loop: • Set initial state of the loop variable • Condition test the loop variable • Modify the state of the loop variable

25. Next Lab Assignment Perl Subroutines Is a named piece of program that can be invoked from elsewhere in the program in order to accomplish some sub-goal of the program. Subroutine Format sub NAME BLOCK   Example: sub subroutine_name { print "Hello, ITEC 400 class. \n"; }

26. Next Lab Assignment my Operator Initially, Perl observes the enclosed block to see what variable(s) are declared in the same block with the “my” declaration. The variable is lexically scoped and doesn’t exist in any other package. It exists only in that lexical scope. This operator declares one or more variables to exist only within the inner most enclosed block. Example: sub subroutine_name { my $name = shift; print "Hello, my name is Gail. \n"; }

27. Next Lab Assignment Shift Function The shift operator takes the next option in the active array. Example: sub subroutine_name{ # Use the presently referenced array. my $name = shift; print "Hello, my name is $name. \n"; } use Declaration The use declaration loads in a module and imports subroutines and variables into the current package from the named module.

28. Next Lab Assignment use Declaration Example: # All possible restrictions are assumed. use strict; # Subroutine correct_msg sub correct_msg{ print_msg(" Good message. \n"); } There are three possible options to be strict about. They are vars, refs, and subs. Strict without options is the safest, but most restrictive mode to operate.

29. Next Lab Assignment Foreach loop Example: foreachVAR (List) { … } Demonstrate Execute read_list.pl script

30. Next Lab Assignment Foreach loop Example: @myNames= ('Larry', 'Curly', 'Moe');foreach(@myNames) { print $_; } Demonstrate Execute sum_list.pl script Execute arry_sort.pl script

31. Next lab assignment Perl Program Statement #!/usr/bin/perl #!/usr/bin/perl–w Print continuation statement print "error: incorrect number of arguments", "\n", "usage: intlist a b (where a < b)", "\n";

32. Next lab assignment Demonstrate Lab Assignment 4-1 Execute linenum.pl and intlist.pl scripts.

33. Break-out problems • $strexp = “This text is considered as a string”; • $intexp = 10; • $floatptexp = 2.54; • $charexp = ‘a’; • $cmdexp = `ls –l`; • $argexp = (“two”, “four”, “six”); • @arrayexp = (“Jackie”, “Vicki”, “Alex”); • $arrayexp[0] = “new value”; • $a = $b + 5; • $container = @container; • ($map{blue}, $map{orange}, $map{jade}) = (0xff0000, 0x00ff00, 0x0000ff0);

34. Next Lab Assignment Programming Perl text book reading Chapter One Chapter Two Chapter Three

35. Next Lab Assignment The following Perl scripts have been copied to the /tmp system directory for you to copy and use personally: substr.pl output_msg.pl sub_arg_pass.pl read_list.pl sum_list.pl arry_sort.pl

36. Upcoming deadlines • Lab Assignment 3-1, Advanced Scripting, due January 31, 2010. • Lab Assignment 4-1, Simple Perl Exercise, due February 7, 2010. • Read Module Three listed under the course Web site.

37. Questions and answers • Questions • Comments • Concerns • After class, I will help students with their scripts.