Perl Tutorial - 2 林光龍

Memory Address (1/3) A number that is assigned to each byte in a computer’s memory that the CPU uses to track where data and instructions are stored in RAM. Each byte is assigned a memory address whether or not it is being used to store data. The computer’s CPU uses the address bus to communicate which memory address it wants to access, and the memory controller reads the address and then puts the data stored in that memory address back onto the address bus for the CPU to use.

Memory Address (2/3) $b = 17; $a = \$b;

$b[2] $b[1] $b[0] $c{“k3”} $c{“k2”} %c $c{“k1”} E015 E001 E013 E017 E033 E031 E035 Memory Address (3/3)

$b[2] $b[1] $b[0] $c{“k3”} $c{“k2”} %c $c{“k1”} E015 E001 E013 E017 E033 E031 E035 \$a \%c Reference (1/2)

Reference (2/2) A reference is a scalar value that points to a memory location that holds some type of data. $a = = (1, 2, 3); %c = ("k1" => "foo", "k2" => "bar"); $add_of_a = \$a; $add_of_b = $add_of_c = \%c; print <<"END"; The address of \$a is $add_of_a The address of is $add_of_b The address of \%b is $add_of_c END

Multi-Dimensional = (' ', 'Sending Mail in Perl', 'Philip = (' ', 'Manipulating Dates in Perl', 'Philip = (' ', 'GUI Application for CVS', 'Philip = The result would be similar to = (' ', 'Sending Mail in Perl', 'Philip Yuson', ' ', 'Manipulating Dates in Perl', 'Philip Yuson', ' ', 'GUI Application for CVS', 'Philip Yuson');

Multi-Dimensional Array Instead of pumping these into one list, you can put the references of these arrays in the = Or to = ( [' ', 'Sending Mail in Perl', 'Philip Yuson'], [' ', 'Manipulating Dates in Perl', 'Philip Yuson'], [' ', 'GUI Application for CVS', 'Philip Yuson']);

To Get Value in Multi-Dimensional Array (1/2) To reference the first column of the first row: $ref = $main[0]; # set $ref to reference $ref->[0]; # Returns the first item To simplify: $main[0]->[0]; You can also simplify this as: $main[0][0]; To get the value of the second column of the third row: $ref = $main[2]; # Third row; $ref->[1]; # second column;

To Get Value in Multi-Dimensional Array (2/2) use strict; = (86, 77, 82, 90); = (88, 70, 92, 65); = (71, 64, 68, 78); = for (my $row = 0; $row < $#grades+1; $row++) { for (my $col = 0; $col < $#{$grades[$row]}+1; $col++) { print $grades[$row][$col]. ", "; } print "\n"; }

Associative Array (1/2) Scalar is the simplest Perl data type which was designed to hold only one thing like a number, a string or a reference. A list is an ordered collection of scalars. An array is a variable that contains a list. A hash is a data structure like an array, in that it can hold any number of values and retrieve these values at will. However, instead of indexing the values by number, as we did with arrays, we'll look up the values by name. That is, the indices (here, we'll call them keys) aren't numbers but are arbitrary unique strings

Associative Array (2/2) 3 $x Dog $y 3 $a[2] 2 1 $a[1] 188 $h{ "he" } Wall Larry $h{ “ln" } $h{ "fn" } %h

Creating a Hash my %weekdays = ( 'Sun' => 'Sunday', 'Mon' => 'Monday', 'Tue' => 'Tuesday', 'Wed' => 'Wednesday', 'Thu' => 'Thursday', 'Fri' => 'Friday', 'Sat' => 'Saturday', ); my %month = ( 'January' => '01', 'February' => '02', 'March' => '03', 'April' => '04', 'May' => '05', 'June' => '06', 'July' => '07', 'August' => '08', 'September' => '09', 'October' => '10', 'November' => '11', 'December' => '12', );

Hash Operation Retrieving a value from a hash. Adding new key/values to a hash. Changing the value of an existing hash key. Deleting a key/value from a hash. my $day_of_the_week = $weekdays{'Wed'}; delete $weekdays{'some'}; $weekdays{'some'} = 'someday';

Hash Function FunctionExample keys(%hashname) $fred{"aaa"}="bbb"; = keys(%fred); $num_of_hash_pair = keys(%fred); values(%hashname) %lastname = (); $lastname{"fred"}="flintstone"; each(%hashname)($key, $val) = each(%lastname) delete $hashname{$key}

%map = qw(red apple green leaves blue ocean); print "A string please: "; chomp($some_string = ); print "The value for $some_string is $map{$some_string}\n" if (defined( $map{$some_string})); # DEFINE A HASH %coins = ( "Quarter", 25, "Dime", 10, "Nickel", 5 ); # LOOP THROUGH IT while (($key, $value) = each(%coins)){ print "($key = $value)\n"; }

Sorting Hashes by Key %grades = ( kim => 96, al => 63, rocky => 87, chrisy => 96, jane => 79, ); print "\n\tGRADES SORTED BY STUDENT NAME:\n"; foreach $key (sort (keys(%grades))) { print "\t\t$key \t\t$grades{$key}\n"; }

Sorting Hashes by Value sub hashValueAscendingNum { $grades{$a} $grades{$b}; } sub hashValueDescendingNum { $grades{$b} $grades{$a}; } %grades = (student1 => 90, student2 => 75, student3 => 96, student4 => 55, student5 => 76,); print "\nGRADES IN ASCENDING NUMERIC ORDER:\n"; foreach $key (sort hashValueAscendingNum (keys(%grades))) { print "\t$grades{$key} \t\t $key\n"; } print "\nGRADES IN DESCENDING NUMERIC ORDER:\n"; foreach $key (sort hashValueDescendingNum (keys(%grades))) { print "\t$grades{$key} \t\t $key\n"; }

The Standard File Handles FunctionDescription STDIN Reads program input. Typically this is the computer's keyboard. STDOUT Displays program output. This is usually the computer's monitor. STDERR Displays program errors. Most of the time, it is equivalent to STDOUT, which means the error messages will be displayed on the computer's monitor. # To read a line from the keyboard and then display it. # This will continue until you press Ctrl+Z on DOS systems or Ctrl-D on UNIX systems. while ( ) { print(); }

$INPUT_FILE = $ARGV[0]; = ; close(INPUT_FILE); foreach { print(); }

21 Reference Perl Tutorial: Start, – – m (Big5 Version) m The perl.ogr Online Library, Beginning Perl – perl.org Perl For CGI tutorials

22 A. D. Marshall, Practical Perl Programming, , Simon Cozens, Ten Perl Myths, February 23, 2000, 簡信昌, Perl 學習手札全文, 朱孝國, Perl 筆記, Perl 的安全性監測, Programmer's File Editor, The CPAN Search Site, Regular Expression Tutorial, expressions.info/tutorial.htmlhttp:// expressions.info/tutorial.html 22