Week Four Agenda

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

2. Link of the week Object Code • http://en.wikipedia.org/wiki/Object_code • What is object code? • What format is object code in? • How are object files applied where large systems are packaged?

3. Proctor & Attendance I still need a proctor from some of you.. You won’t be able to take the midterm until a proctor is approved A reminder that attendance is kept for this course, and you receive 10 points for each session you attend (~130 points total) – you can turn in summaries up to the time the Saturday after the session missed.

4. Logic scripts • “..” needs your input – typically expressions for if statements, but may need other commands, like echo, print, etc.. • “variable” or $variable – needs you to change it to a variable name of your choice – just be consistent • Future logic scripts may include “syntax” errors, or typos that you need to correct to make the script run properly. • You may see $? – or index number in scripts which also means for you to supply a variable name • Don’t forget the comments at the top (Author, Function, Lab Assignment, Date, etc.)

5. Link of the week

6. Link of the week

7. Review Week Three Lab Assignment What is a filter? A UNIX filter command performs an operation or manipulation of text in a file. Standard in and out are typically used during this operation. Shell Command Line Filters awk, cat, cut, expand, compress, fold, grep, head, nl, perl, pr, sed, sh, sort, split, strings, tail, tac, tee, tr, uniq, and wc

8. Review Week Three Lab Assignment Shell File System Filters cat, cd, chmod, chown, chgrp, cksum, cmp, cp, dd, du, df, fsck, fuser, ln, ls, lsattr, lsof, mkdir, mount, mv, pwd, rm, rmdir, split, touch, umask Shell Process Filters at, chroot, cron, exit, kill, killall, nice, pgrep, pidof, pkill, ps, pstree, sleep, time, top, and wait

9. Review Week Three Lab Assignment Test Command A common way to set up a condition for the if command is with the test command. test condition or [ condition ] The test command evaluates the condition and returns 0 or 1, depending on the results of the test. The brackets work exactly like the test condition. The open bracket is a link to test.

10. Review Week Three Lab Assignment Constructing Conditions -s file -r file -w file -x file -f file -d file Examples: if [ ! –f /etc/.fsckask ] If the plain file /etc/.fsckask does not exist If [ -d /etc/rc0.d ] If there is a directory named /etc/rc0.d

11. Review Week Three Lab Assignment Commands cal –y (display a calendar 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 2010 month)

12. 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.

13. 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.

14. Review week three lab assignment 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 The return value for a child process is returned to the parent process when the child process terminates.

15. Review week three lab assignment $? – 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

16. 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>>

17. Review week three lab assignment 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. open functions open(file_handler, “file_name”) open(file_handler, “<file_name”) open (file_handler, “>file_name”) open (file_handler, “>>file_name”)

18. 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

19. 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

20. Week four expected outcomes • Write Perl scripts, including variables, control flow, and regular expression syntax

21. Next lab assignment • Perl is designed to - Process text data - Perform pattern matching - Utilize string handling tasks • Perl is available on many platforms - UNIX - Linux - HP-UX

22. 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 $. - Plural variables are ones that contain multiple-values. Arrays and hashes are two multi-valued variables. 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)

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

24. 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.

25. Next Lab Assignment open functions open(file_handler, “file_name”) open(file_handler, “<file_name”) open (file_handler, “>file_name”) open (file_handler, “>>file_name”)

26. Next Lab Assignment Filehandle is 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);

27. Next Lab Assignment What is List Processing? @math_array = (6 - 4, 4 * 4, 8 / 2, 9 - 8); while ( … ) { … } 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

28. Next Lab Assignment foreach VAR (List) { … } Demonstrate: Execute read_list.pl script @myNames = ('Larry', 'Curly', 'Moe');foreach (@myNames) { print $_;} Demonstrate: Execute sum_list.pl script

29. 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"; Demonstrate: Execute linenum.pl and intlist.pl scripts.

30. Next lab assignment Demonstrate Execute arry_sort.pl script Programming Perl text book reading Chapter One Chapter Two Chapter Three

31. Upcoming deadlines • Advanced Shell Script, Lab Assignment 3-1 is due Jan. 29. • Simple Perl Script, Lab Assignment 4-1 is due Feb. 5. • Mid-term outline to be posted online on or before Jan. 30. • Mid-term exam, (Lab Assignment 7-1) dates Feb. 13-18 • Makefile Exercise, Lab Assignment 6-2 is due Feb. 19. • Lab Assignment 6-1 is due Feb. 26

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