Week Five Agenda Announcements Link of the week Review week four lab assignment This week’s expected outcomes Next lab assignment Break-out problems Read assignments Upcoming deadlines Lab assistance, questions and answers

Announcements The midterm exam is electronic. Please verify that your proctor can administer this type of test. The midterm exam outline has been posted under the Bulletin Board.

Link of the week Data Disaster Ontrack Data Recovery Ironkey USB Flash Drive Data Disaster Helpful Hints - Use dedicated circuits for your connection - Keep your computer cool and in a dry place - Use a UPS (Uninterrupted Power Supply) - Don’t assume that your data is permanently destroyed even if the situation looks bad - Secure your work area and devices

Link of the week Data Disaster 1.Big and small company operations 2.Backup services 3.Trouble shooting 4.Data recovery

Review week four lab assignment What is an object file? Object code is a representation of code generated by a compiler after it processes a programming language code file. It contains compact, pre-parsed code, often referred to as binaries that can be linked with other object files to generate a final executable.

Review week four lab assignment What is ELF? Executable and Linking Format (ELF) is a common standard file format for executables, object code, shared libraries, and core dumps.

Review week four lab assignment Online Documentation There are some websites that have Perl documentation. The two biggest ones are: for modules

Review week four lab assignment Perl Syntax ;End of statement delimiter,Comma for line continuation \nNew line (non-printable character) <> The "diamond operator", <> is used when a program is expecting input, but isn't concerned how it arrives. Demonstrate: diamond_oper.pl

Review week four lab assignment Perl Variable Syntax $ Singular variables prefix (single value, number or Prefix for plural variable (array) %Prefix for plural variable (hash) $_ Default variable It Is the "it" variable. It's often the default parm that built-in functions use, or return into. $0Contains the name of the program being run

Review week four lab assignment Perl Syntax while ( … ) { Action statements } What is a continuous loop? while ( 2 ) { Action statements } Demonstrate: perl_it.pl

Review week four lab assignment Perl Syntax If ( … ) { Action statements } elsif { Action statements }

Review week four lab assignment Perl Syntax The Perl language does not support case or switch statements. The closest way to achieve case evaluations is as follows:

Review week four lab assignment Perl Procedural Syntax if (variable == 1) { statement_1"; } elsif (variable == 2) { statement_2"; } elsif (variable == 3) { statement_3"; } else { default_statement"; }

Review week four lab assignment Perl Switch Syntax switch(variable) { case 1: statement_1"; break; case 2: statement_2"; break; default: default_statement; }

Review week four lab assignment Perl Syntax If ( …) { Action statements }

Review week four lab assignment Three Types of for loops # Old style C for loops for (my $i = 0; $i < 10; $i++) { $array[$i] = $i; } # Iterating loops for my $i { print "$i\n"; }

Review week four lab assignment Three Types of for loops (continued) # Postfix for loops print "$_\n"

Review week four lab assignment Perl Syntax foreach $total (12,9,3,7) { # Sum each value in the list. $sum += $total; }

Review week four lab assignment Perl Syntax foreach (-32,10,1,2,0,-1) { # Valid numbers are considered to be greater than zero # The default variable is utilized, if ( $_ > 0 ) { # Print each valid number on a single output line. print "$_\n"; }

Review week four lab assignment Relational Operators NumericStringMeaning > gtGreater than >= geGreater than or equal to < ltLess than <= leLess than or equal to

Review week four lab assignment Equality Operators NumericString Meaning == eq Equal to != ne Not equal to  cmp Comparison with signed result The  or cmp operators return 1 if the left operand is less than the right operand, 0if they are equal, and +1 it the left operand is greater than the right.

Review week four lab assignment Definition: array Arrays are an ordered list of scalars, accessed by the scalar’s position in the list. Otherwise known as a collection of scalars. In Perl, a scalar means the simplest data type which was designed to hold only one thing like a number, a string or a reference. Elements in an array are accessed by using an index. Array indexes start with zero.

Review week four lab assignment Array and Variable Initialization Initialize an = (“rake”, “mower”, = (“Will”, “Ken”, “Hazel”, “Jay”); $count Unload array elements into variables: ($rake, $mower, $shovel)

Review week four lab assignment Array Data Structures Array of arrays – Two-dimensional array or a = ( [ “Brenda”, “Clide”, “Kim” ], [ “Melinda”, Terri”, “Sissy” ] [ “Fred”, “Omar”, “Vincent” ] ); print $names [1] [1]; Demonstrate: ~dandrear/Winter_2012_Solutions/two_dim.pl

Review week four lab assignment Definition :Hash (associative array) A hash is similar to an array only because it contains a number of scalars. A hash is different in the case where the element of a structure represents a pair – a key and a value. Whenever we refer to an element of a Perl hash structure, we mean a pair (key and value) which links a value to a key. We have access to the elements of a hash variable by a scalar key. A hash table is an unordered set of scalars, accessed by some string value that is associated with each scalar.

Review week four lab assignment Keys John Smith Lisa Smith Sam Doe Sandra dee Hashes

Review week four lab assignment

Hash Function Some cryptographic hash functions, such as SHA-1, have even stronger uniformity guarantees than checksums or fingerprints, and thus can provide very good general- purpose hashing functions

Review week four lab assignment Hash Initialization %student_ages = ("John", 43, "Paul", 25, "Marie", 22); %members = (John => "father", Paul => "son", Marie => "daughter"); The comma-arrow (=>) operator is used to initialize the %members hash variable in the second line of code. The left side of the comma- arrow operator is expected to be a simple string and therefore it is not necessary to be quoted.

Review week four lab assignment Hash Initialization (con’t) %all_groups = ( group_name1 => [ “Betty”, “Tom”, “Moe” ], group_name2 => [ “Ali”, “Marcia”, “Sis” ] ); $all_groups{group_name1} [3] = “Sam”; for $couple ( keys %all_groups ) { print }\n; }

Review week four lab assignment Hash Copy %school_ages = %student_ages Demonstrate: ~dandrear/Winter_2012_Solutions/hash_table. pl

Review week four lab assignment Hash Table Example %colormap=( “12” => “gray”, “19” => “black”, “30” => “red”,); %colormap = (“12”, “gray”, “19”, “black”, “30”, “red”);

Review week four 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. The variable prefix symbols for an array and hash and %, respectively.

Review week four lab assignment Perl data types $answer = 42; (an integer) $pi = ; (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) Perl utilizes dynamic data typing of variables.

Review week four 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);

Review week four lab assignment Practice scripts under the system /tmp directory awksrc diamond_oper.pl person.sh perl_it.pl two_dim.pl names hash_table.pl test_build.sh

Weeks four and five expected outcomes Write Perl scripts, including variables, control flow, and regular expression syntax

Next lab assignment Regular Expressions Search programs – grep, egrep, and findstr. Text language programs - sed and awk Text editors – iv and emac Many other languages use regular expressions and may advertise a particular version of Perl.

Next lab assignment Regular Expression Special Characters * Open square bracket [ * Backslash\ * Caret^ * Dollar sign$ * Dot. Pipe symbol| Question mark? Asterisk* * Plus sign+ Opening and closing round brackets( )

Next lab assignment Regular Expression (a.k.a. regex or regexp) Is a pattern that describes a certain amount of text. A basic regular expression could be the single character, e.g.: a Jack is a guy. It will match the first occurrence in the string. If succeeding matches are desired, the regex engine must be instructed to do so.

Next lab assignment Character Classes match only one out of several characters, e.g.: [ae] and gr[ae]y The order of the characters inside a character class doesn’t matter. Shorthand Character Classes match single characters, e.g.: \d and \w and \s and \t Non-Printable Characters are special character sequence to put non-printable characters in your regular expression, e.g.: \t and \r and \n and \a and \e and \v

Next lab assignment Dot matches almost any character, except line break characters, e.g.: gr.y Anchors match a position. Match start of string^ Match end of a string$ Alternation is the regular expression equivalent of “or”. The search pattern bird | insect will first return “bird. The second match will be “insect”.

Next lab assignment names Bob D'Andrea /19/1947 male Bo Happy /01/1945 male Jane Smith /23/1978 female Razi Jake /26/2005 male The file named “names” contains the above information. There are tabs in two places in the above data. One tab is after the name and after the birth date.

Next lab assignment Without options, print the desired fields in any order. awk ‘{ print $1, $2, $3, $4 }’ names The –F option changes the field separator on the command line. The \t is an Escape Sequence for a horizontal tab. awk –F”\t” ‘{ print $1 }’ names

Next lab assignment makefile Lab Assignment Copy the test_build.sh script from ~dandrear/tmp directory This script executes the make command which in turn executes the makefile Demonstrate and display: ~dandrear/temp/test_build.sh

Next lab assignment Programming Perl, Chapter 32 Standard Modules Define: Module Parsing the command line with Getopt::Std Example: listdir –l –n –a 10:00 bottom top Perl to capture the command line arguments Example: $ARGV[0] ‘-l’ $ARGV[1]‘-n’ $ARGV[2]‘-a’ $ARGV[3]’10:00’ $ARGV[4]‘bottom’ $ARGV[5]‘top’

Break-out problems Define a Perl hash table Define ELF Define a Perl array What convenience does a Perl filehandle provide? What is the functionality of a regular expression? Are continuous loops useful? Define an object file Define common-arrow Perl default variable Perl “it” variable Explain the s/pattern/new version/ command

Reading assignments Reading Assignment Essential System Administration Chapter One Chapter Two Chapter Three Programming Perl Chapter One Chapter Two Chapter Three Chapter Four Chapter Thirty Two (review)

Upcoming deadlines Lab Assignment 4-1 due February 15, Lab Assignment 6-1 due February 26, Lab Assignment 6-2 due February 19, Lab Assignment 7-1 Midterm exam will be administered from February 13 through 18.

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