1. Basic Perl Programming
Introduction:
Perl - Practical Extraction and Report Language
Using interpreter to run on the system (windows/unix/linux perl interpreter)
Very powerful for handling and manipulate text
Usually with *.pl file/script extension

2. Getting Perl
In Linux/Unix OS it has become a standard package installed
For Windows OS get it from:

3. Basic Perl Programming
My first Perl program (Say hello to Perl)
#! /usr/bin/perl
# print a words "Say hello to Perl"
print "Say hello to Perl.\n";

4. Basic Perl Programming
Basic Standard Input/Output
#! /usr/bin/perl
print "\nPlease enter your name: ";
$user_name = <STDIN>;
print "\nHello ", $user_name,
"Please say hello to Perl\n";

5. Basic Perl Programming
Variable (Scalar)
must be preceded with ‘$’ sign
no specific data types (int, float, char)
#! /usr/bin/perl
$food = "2-Piece Chicken";
$drink = "Pepsi";
print "Food = $food\n";
print "Drink = $drink\n\n";
$food = 4.59;
$drink = 1.7;
print "Food price= $food\n";
print "Drink price= $drink\n";
print "Total price= ", $drink + $food, "\n";

6. Basic Perl Programming
Exercise 1:
Write Perl script to ask student to enter name, , and course. The script will later print out all the information entered.

7. Basic Perl Programming
Variable (Array)
preceded with sign
several ways to define array:
@food = (“”);
$food[0] = “2-Piece Chickens”;
$food[1] = “Kentucky Nuggets (6 Pieces)”;
$food[2] = “Deli Burger”;
@drink = (“Pepsi”, “Ice Lemon Tea”, “Orange Juice”);

8. Basic Perl Programming
Variable (Array)
syntax to get an array element: $array_variable_name[index_value];
retrieve the number of item and length of index of array variable:
$items # $ items will get the value of 3
$length = $#drink # $length will get the value of 2

9. Basic Perl Programming
Variable (Array)
define and assign a value of array variable using split function
$f_price = “ ”;
@food_price = split(/ /, $f_price);
@drink_price = split(/:/, “1.70:2.20:2.20”);

10. Basic Perl Programming
Exercise 2:
Modify the script from exercise 1 so it can handle more than single student information.

11. Basic Perl Programming
Variable (Hash)
a series pairs of keys and values
Preceded with “%” sign
The syntax to define hash: %hash_var = ( key_1 => “value_1”, … , key_n => “value_n” );

12. Basic Perl Programming
Variable (Hash)
The other possible way to assign keys and values to hash: %hash_var = undef; $hash_var{key_1} = “value_1”; … $hash_var{key_n} = “value_n”;

13. Basic Perl Programming
Variable (Hash)
Example:
%food = ("");
$food{fruit} = "Apple";
$food{animal} = "Beef";
%drink =(natural=>"Mineral Water",
carbonate=>"Coca-Cola");

14. Basic Perl Programming
Variable (Hash)
syntax to get hash element: $hash_var_name{key};
get all keywords from hash and store it in an array
@array_var_name = keys(%hash_var_name);

15. Basic Perl Programming
Variable (Hash)
Access hash keys name: @keys = keys(%hash_var); print "\$keys[0] = $keys[0] \n"; print "\$keys[1] = $keys[1] \n"; print "\$keys[.] = $keys[.] \n"; print "\$keys[n] = $keys[n] \n";

16. Basic Perl Programming
Variable (Hash)
Access and assign value to specific hash key: print “$keys[0]= ” , $hash_var{$keys[0]}, “\n”; $hash_var{$keys[0]} = “other value”; print “$keys[0]= ” , $hash_var{$keys[0]}, “\n”;

17. Basic Perl Programming
Copying,Referencing & De-referencing Variable
Copying variable: $my_var = “hello”; $other_var = $my_var;
print “$my_var : $other_var \n”;
$other_var = “olleh”;

18. Basic Perl Programming
Referencing & de-referencing variable: $my_var = “hello”; $other_var = \$my_var;
print “$my_var : $$other_var \n”;
$$other_var = “olleh”;

19. Basic Perl Programming
Explanations: $other_var = \$my_var; -> this will caused $other_var store the address refer by $my_var
$$other_var; -> this is the way we assign/access the value
stored by the address
$$other_var = “olleh”; -> this will caused address refer by both $my_var & $other_var had a new value (“olleh”)

20. Basic Perl Programming
Referencing & de-referencing array & hash: @my_array = (“One”, “Two”); %my_hash = (1 => “One”, 2 => “Two”); $array_ref = $hash_ref = \%my_hash; #de-referencing array & hash ${$array_ref}[0] or $array_ref->[0]; ${$hash_ref}{2} or $hash_ref->{2};
#copy array & hash from reference
@other_array
%other_hash = %{$hash_ref};

21. Loop and control statement
Basic Perl Programming
Loop and control statement
if (…){}
Executes when a specified condition is true
if (…) {} else {}
Chooses between two alternatives
if (…){} elsif() {} else {}
Chooses between more than two alternatives
for (…) {}
Repeats a group of statements a specified number of times
foreach $var_name1
Special loop to access all elements in array variable
while(…) {}

22. Basic Perl Programming
Comparison Operators
Integer-Comparison Operators
Operator
Description
<
Less than
>
Greater than ==
Equal to
<=
Less than or equal to
>=
Greater than or equal to !=
Not equal to

23. Basic Perl Programming
Comparison Operators
String-Comparison Operators
Operator
Description lt
Less than gt
Greater than eq
Equal to le
Less than or equal to ge
Greater than or equal to ne
Not equal to

24. Basic Perl Programming
Exercise 3:
Extend the script from exercise 2 so it can handle other new input (student’s CPA). Based on the CPA value determine either they get 1st, 2nd, or 3rd class following the given conditions below:
CPA
Class
3.7 and above
1st
2.0 – 3.69
2nd
Below than 2.0
3rd

25. Basic Perl Programming
Pattern matching and string manipulation
The syntax for pattern matching:
$string_variable =~ /pattern_to_match/opt;
Example:
$str = “Hello World”;
if ($str =~ /lo/) {
print “Found it.\n”;
} else {
print “Not found.\n”; }

26. Basic Perl Programming
Pattern matching and string manipulation
The syntax for pattern replacement:
$string_variable =~ s/pattern_to_replace/replacement/opts;
Example:
$str = “Hello World”;
$str =~ s/l/m/g;

27. Basic Perl Programming
Pattern matching and string manipulation
Options (opts) for pattern matching & replacement
Option
Description g
Change all occurrences of the pattern i
Ignore case in pattern e
Evaluate replacement string as expression (only for substitution operator) m
Treat string to be matched as multiple lines o
Evaluate only once s
Treat string to be matched as single line x
Ignore white space in pattern

28. Basic Perl Programming
Pattern matching and string manipulation
Regular expression in the pattern (pattern_to_replace)
Meta-characters
Char
Meaning ^
beginning of string ?
match 0 or 1 times $
end of string |
alternative .
any character except newline ()
grouping *
match 0 or more times []
set of characters +
match 1 or more times {}
repetition modifier
To present these meta-characters as a character itself use the ‘\’ character before each meta-characters. Examples: \^, \$, …

29. Basic Perl Programming
Pattern matching and string manipulation
Regular expression in the pattern (pattern_to_replace)
How to know if the string hold by the scalar $plate_no is a valid Johor’s car plate number?
- All letters must be capital start with ‘J’ ^J
- The trailing letters not more than 2 and not including the ‘I’, ‘O’, and ‘Z’ letters
^J[A-H,J-N,P-Y]{1,2}
- Ending with numbers not starting with ‘0’ and not more than 4 in total
^J[A-H,J-N,P-Y]{1,2}[1-9]{1}[0-9]{0,3}

30. Basic Perl Programming
Pattern matching and string manipulation
String manipulation functions
Function
Description
index (string, substring)
Identify the location of a substring in a string.
rindex (string, substring)
Similar to the index function but starts searching from the right end of the string.
length (string)
Returns the number of characters contained in a character string.
substr (string, num_of_skip_char, length)
Returns a part of a character string.
lc(string)
Converts a string to lowercase.
uc(string)
Converts a string to uppercase.

31. Basic Perl Programming
Pattern matching and string manipulation
String concatenation:
#! /usr/bin/perl
$string1 = “The first string ”;
$string2 = “The second string”;
$my_string = $string1 . “ and ” . $string2 ;
print “$my_string \n”;

32. Basic Perl Programming
File Input/Output
Read Operation:
if(open(MYFILE, "<directory/file_name")){
@array_var = <MYFILE>;
. . .
close(MYFILE); }

33. Basic Perl Programming
File Input/Output
Write Operation:
if(open(MYFILE, “>directory/file_name")) {
. . .
print MYFILE ($var_store_file_content);
close(MYFILE); }

34. Basic Perl Programming
Exercise 4:
Modify the script from exercise 3 so the output would also be available as an HTML file. Use the template below as a basic structure of the HTML file content.
<html>
<body>
<table>
<tr><td>Name</td><td>CPA</td><td>Class</td></tr>
<tr><td>_name_</td><td>_cpa_</td><td>_class_</td></tr>
</table>
</body>
</html>

35. Basic Perl Programming
Subroutine/Function
Create a subroutine in Perl script :
sub subroutine_name {
. . . }
Calling a subroutine:
&subroutine_name;

36. Basic Perl Programming
Subroutine
Skeleton of perl script that using a subroutine:
#! /usr/bin/perl
. . .
&subroutine_name;
sub subroutine_name { }

37. Basic Perl Programming
Subroutine
Example:
#! /usr/bin/perl
print "Perl script welcoming the users.\n\n";
&welcome_user;
sub welcomeUser {
print "Your name please: ";
$name = <STDIN>;
chop($name);
print "\nHello $name, welcome to Perl world.\n\n"; }

38. Basic Perl Programming
Subroutine
Pass and return values to/from subroutine
make a subroutine more flexible and useful
based on three guidelines :
The subroutine can accept more than one scalar variable and only one array variable
If the subroutine accept both scalar and array variables the array variable must appear last in the arguments
The first two guidelines above can be ignored by passing array/hash as a reference

39. Basic Perl Programming
Subroutine
Pass and return values to/from subroutine
The Skeleton:
sub subroutine_name {
$scalar_var_name_1 =
. . .
$scalar_var_name_n =
@array_var_name
return (value); }

40. Basic Perl Programming
Subroutine
Pass and return values to/from subroutine
Calling a subroutine that can accept and return values:
$var_name = &subroutine_name(scalar1, . . ., scalarN, array);

41. Basic Perl Programming
Subroutine
Pass and return values to/from subroutine
The story so far:
To return a value the command: return (value); is used inside the subroutine where value can be either scalar, array or result of an expression
When values passed to the subroutine, all the values are stored in the special array variable named @_
The subroutine must extract all the values from this special array variable and pass it to the appropriate variables following the guidelines given previously

42. Basic Perl Programming
Subroutine
Pass and return values to/from subroutine
The story so far:
To return a value the command: return (value); is used inside the subroutine where value can be either scalar, array or result of an expression
When values passed to the subroutine, all the values are stored in the special array variable named
The subroutine then must extract all the values from this special array variable and pass it to the appropriate variables using the two guidelines above

43. Basic Perl Programming
Subroutine
Pass and return values to/from subroutine
The story so far:
The command: will extract and shift the first item
The will assigns all the values
Example:
contains the values: (“A”, “B”, “C”)
The command $var_name = will extract the first item which is “A”, pass it to $var_name and left with the values: (“B”, “C”)
The next will make the contains the values: (“B”, “C”)

44. Basic Perl Programming
Exercise 5:
Modify the script from exercise 4 so the core tasks are written modularly using subroutines/functions.

45. Basic Perl Programming
Subroutine
Writing subroutines as a libraries
The technique for writing a subroutine before caused the subroutine can only be used by the script who implementing them
Writing subroutines as a libraries provide more flexible subroutine that can be used many times by other scripts

46. Basic Perl Programming
Subroutine
Writing subroutines as a libraries
Skeleton for writing subroutine as a libraries:
package library_name;
subroutines goes here . . . 1;
The scripts that are intended to be a libraries must be saved as library_name.pl
The: 1; at the end of libraries script is a mandatory so the perl interpreter can call and run the libraries correctly

47. Basic Perl Programming
Subroutine
Writing subroutines as a libraries
Calling and use subroutine from the libraries:
#! /usr/bin/perl
require (“library_name.pl");
. . .
$val = &library_name’subroutine_name1;
&library_name’subroutine_name2(. . .);

48. Basic Perl Programming
Subroutine
Variable scope:
#! /usr/bin/perl
$name = "Your name";
print "\$name: $name\n";
&change_name;
print "\Sname: $name\n";
sub change_name {
my $name = "My name"; }
#! /usr/bin/perl
$name = "Your name";
print "\$name: $name\n";
&change_name;
print "\Sname: $name\n";
sub change_name {
$name = "My name"; }