1. Advanced Topics
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2. Reference/Pointer A reference Syntax
a pointer to something (e.g. array, hash)
a variable that refer to other variables
contain a memory address of data
good for
working with large data structures
creating complex data structures
Syntax
to create a reference
$ptr1= \$scalar; $ptr2= $ptr3= \%hash;
$ptr4= [1, 2, 3]; $ptr5= { k1=>v1, k2=>v2}
to get the value
Variable (i.e. scalar, array, hash)
$$ptr1; @$ptr2; %$ptr3;
Element of array/hash
$$ptr2[0]; $$ptr3{0};
$ptr2->[0]; $ptr3->{0};
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3. Multi-dimensional Arrays
Using anonymous arrays
$array = [ [id1,pw1], [id2,pw2], [id3,pw3] ];
for ($i=0; $i<=2; $i++) { for ($j=0; $j<=1; $j++) { print “$array -> [i][j]\n”; }
Using array references
@a1= (id3,pw3);
@array = # array of array pointers
for ($i=0; $i<=2; $i++) {
$ptr= $array[$i];
print
Examples: #1, #2, #3, #4, #5
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4. Fetching Web pages with LWP
use LWP::Simple;
$url=
$body= get($url);
print $body;
Example script
use LWP::UserAgent;
$ua = LWP::UserAgent->new();
$resp= $ua->get($url);
$content=$resp->content();
print $content;
Example script Form CGI
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5. WWW-Mechanize Module a subclass of LWP::UserAgent Basics Create a mech
use WWW::Mechanize;
my $mech = WWW::Mechanize->new( autocheck => 1 );
Fetch a page
$mech->get( " );
print $mech->content;
Fetch a page into a file
$mech->get( " ":content_file" => “hello.htm" );
Get Links
@links= $mech->links(); array of link object
foreach {
my($url,$text,$absurl)= ($link->url(), $link->text, $link->url_abs());
print “$url, $text, $absurl\n”; }
Find Links
$link= $mech->find_link(url_abs_regex=>qr|^
$page= $mech->follow_link(url_abs_regex=>qr|^
@pages= $mech->follow_all_links(url_abs_regex=>qr|^
Mechanized Spider Example: #1, #2, #3
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6. Perl DBI Module Basics Connect to a database Execute SQL Retrieve data
use DBI;
my $dbh = DBI->connect( DBI:Pg:dbname=$dbname; host=$host; $user, $pw ) || die “Can’t connect to DB: $DBI::errstr\n”;
Execute SQL
my $sql = “SELECT * FROM $table;
my $sth = $dbh->prepare($sql);
$sth->execute();
Retrieve data
while $sth->fetchrow_array()) {;
print join (“, }
Disconnect from the database
$dbh->disconnect();
Example Script: #1, #2
Perl DBI Manual
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7. Miscellaneous Features
require “mylib.pl”
store and use common subroutines in mylib.pl
looks for mylib.pl directory
add “return 1” at the end of “mylib.pl”
example: mylib.pl, calling script #1
perlcc prog.pl –o prog.out
generates a compiled binary named “prog.out”
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