Beginning Perl Third Edition PHẦN 10 docx

That produces this page: And here’s the code that builds the page: } elsif param'Show instruments' { # the user wants to see the instruments the musician # plays, start the HTML p

After calling Geddy Lee, our music fan might want to see the instruments Thom Yorke plays, so our

curious person goes back to the initial page, select Thom from the drop-down menu, and clicks Show

instruments That produces this page:

And here’s the code that builds the page:

} elsif (param('Show instruments')) {

# the user wants to see the instruments the musician

# plays, start the HTML

print

header(),

start_html("Instruments played by $musician"),

h1("Instruments played by $musician"),

"$musician plays:",

'<ul>';

385

We see that the user wants to show the musician’s instruments, so we start the HTML, print some text, and then start an unordered list (a bullet list) Then we go to the code that queries the database:

# query the database with a table join and retrieve the

# instruments played by musician

my $dbh = DBI->connect("DBI:mysql:musicians_db", "musicfan",

"CrimsonKing");

my $sth = $dbh->prepare("SELECT instrument

FROM instruments

JOIN what_they_play ON instruments.inst_id = what_they_play.inst_id

JOIN musicians ON what_they_play.player_id = musicians.player_id

WHERE musicians.name = ?")

or die "prepare failed: " $dbh->errstr();

$sth->execute($musician) or die "execute failed: " $sth->errstr();

Using the table join we’ve seen a few times in this chapter, we find all the instruments that the musician plays, bringing us to the code that prints the instruments:

my($instrument);

# print all the instruments in a bullet list

while (($instrument) = $sth->fetchrow()) {

print "<li>$instrument</li>";

}

Notice that each instrument is printed within an <li> tag, which makes it into a bullet item in the list

Finally we get to the end of the unordered list and the end of the HTML:

What We Didn’t Talk About

This chapter isn’t meant to be an exhaustive discussion of SQL and DBI There are many topics we didn’t

talk about that you should learn if you want to harness the maximum power of SQL First, there are

several essential commands, including the following:

• UPDATE: Allows data in a table to be modified An example might be

UPDATE musicians SET phone = "555-9999" WHERE player_id = 3;

386

• DELETE: Deletes a row from a table An example might be

DELETE FROM instruments WHERE inst_id = 13;

Be careful! If you don’t use the WHERE clause, you’ll delete all rows in the table

• REPLACE: If the key provided does not exist, the data is inserted; otherwise the row

with that key is first deleted, then the new row is inserted An example might be

REPLACE INTO musicians (player_id, name, phone) VALUES (1, "Neil Peart", "555-8888");

Just as knowing these SQL commands is important, so is understanding table indexing Indexing can

significantly increase the speed of SELECT statements with large tables See the docs for more

information Also, be sure to check out Michael Kofler’s excellent book, and remember to look at the

online documentation for MySQL at http://dev.mysql.com/doc/refman/5.1/en/

Summary

In this chapter we described how to access a database using Perl and the DBI module We started with a

description of a relational database and followed with a brief introduction to SQL We then installed

MySQL, created a database with three tables, and talked about several SQL commands INSERT and

SELECT were the most important ones We also discussed using table joins as a way to implement the

relations in relational databases After that, we introduced DBI and DBD::mysql and wrote several Perl

scripts to access and query the database We ended with an example that showed how easily you can

create dynamic web content by connecting Perl, DBI, and CGI.pm And in the middle of that discussion,

we took time out of our busy day to call one of our favorite musicians

Exercises

1 Write a Perl script that prompts the user for an instrument and then prints all the

musicians that play that instrument

2 Write a CGI program similar to musicians.pl that serves as a web interface to the script you

created for exercise 1

■ ■ ■

387

Exercise Solutions

This appendix contains the answers to the chapter exercises An important note: each solution is an

answer, not the answer Remember that in Perl, there is more than one way to do it, and that applies to

these solutions as well

print "Currency converter\n\n";

print "Please enter the exchange rate: ";

chomp(my $yen = <STDIN>);

388

print "Enter first price to convert: ";

chomp(my $price1 = <STDIN>);

print "Enter second price to convert: ";

chomp(my $price2 = <STDIN>);

print "Enter third price to convert: ";

chomp(my $price3 = <STDIN>);

print "$price1 Yen is ", ($price1/$yen), " dollars\n";

print "$price2 Yen is ", ($price2/$yen), " dollars\n";

print "$price3 Yen is ", ($price3/$yen), " dollars\n";

print "enter a hex number: ";

chomp(my $hexnum = <STDIN>);

print "converted to an int: ", hex($hexnum), "\n";

print "enter an octal number: ";

chomp(my $octal = <STDIN>);

print "converted to an int: ", oct($octal), "\n";

print "enter a value less than 256: ";

chomp(my $bin = <STDIN>);

print((128 & $bin) / 128);

print((64 & $bin) / 64);

print((32 & $bin) / 32);

print((16 & $bin) / 16);

print((8 & $bin) / 8);

print((4 & $bin) / 4);

print((2 & $bin) / 2);

www.wowebook.com

print "Guess my number!\n";

print "Enter your guess: ";

} elsif ($guess > $target) {

print "Your number is more than my number\n";

} elsif ($guess < $target) {

print "Your number is less than my number\n";

390

use warnings;

use strict;

for (my $i = 1; $i <= 10; $i++) {

print "$i square is: ", $i*$i, "\n"; }

scalar => 'dollar sign',

array => 'at sign',

hash => 'percent sign'

Java => "None Change it once, and it's the same everywhere.",

Python => "One He just stands below the socket and the world "

"revolves around him.",

Perl => "A million One to change it, the rest to try and do it in " "fewer lines.",

print "enter a number: ";

chomp(my $input_num = <STDIN>);

# here is the solution using recursion -

# a recursive function is a function that calls

Match “hello” followed by zero or more and any character but \n followed by “world”; or, in other words,

any string that contains “hello” followed later by “world”

Match one or more digits at the beginning of the string followed by one whitespace character

followed by zero or more word characters followed by the end of the string

Match an uppercase letter at the beginning of a word followed by zero or more lowercase letters to the end of a word; or, in other words, match a word that begins with an uppercase letter followed by any number of lowercase letters

Match a character, remember it in \1, followed by any number of any characters but \n, followed by

the character remembered In other words, match any string with two occurrences of the same

open(INFH, '<', 'gettysburg.txt') or die $!;

open(OUTFH, '>', 'ex1out.txt') or die $!;

print "File already exists What should I do?\n";

print "(Enter 'r' to write to a different name, ";

print "'o' to overwrite or\n";

print "'b' to back up to $target.old)\n";

my $choice = <STDIN>;

chomp $choice;

if ($choice eq "r") {

next;

} elsif ($choice eq "o") {

unless (-o $target) {

print "Can't overwrite $target, it's not yours.\n";

last if open(OUTPUT, '>', $target);

print "I couldn't write to $target: $!\n";

# and round we go again

}

print OUTPUT "Congratulations.\n";

print "Wrote to file $target\n";

die "usage: chap10ex1.pl <dir> <size>\n" unless $dir and $size;

chdir $dir or die "can't chdir: $!";

# first, a file glob

# this gets hidden files too

print "using glob:\n";

# now using a directory handle

print "\n\nusing directory handle:\n";

opendir DH, '.' or die "opendir failed: $!";

while ($_ = readdir(DH)) {

if (-f $_ and -s _ >= $size) {

print ' ', $_, ' ' x (30 - length($_)), -s _, "\n";

print "\n$chessboard[$endy][$endx] at (", $endx + 1, ",",

$endy+1, ") is being taken!\n\n";

$chessboard[0]->[$_] = "W" $back[$_]; # White Back Row

$chessboard[1]->[$_] = "WP"; # White Pawns

$chessboard[6]->[$_] = "BP"; # Black Pawns

$chessboard[7]->[$_] = "B" $back[$_]; # Black Back Row

unless (defined $chessboard[$starty][$startx]) {

print "There's nothing on that square!\n";

print "Enter name: ";

chomp(my $name = <STDIN>);

print "Enter name to view: ";

chomp(my $name = <STDIN>);

if (exists $addressbook{$name}) {

print "Address: $addressbook{$name}{address}\n";

print "Phone: $addressbook{$name}{phone}\n\n";

foreach my $name (sort keys %addressbook) {

print "Name: $name\n";

print "Address: $addressbook{$name}{address}\n";

print "Phone: $addressbook{$name}{phone}\n\n";

}

}

sub delete_entry {

print "Enter name to delete: ";

chomp(my $name = <STDIN>);

if (exists $addressbook{$name}) {

delete $addressbook{$name};

print "There are ", Person8->headcount(), " Person8 objects\n";

foreach my $person (Person8->everyone()) {

h1('Thanks for your information!'),

'Thanks for entering the following information:',

my $dbh = DBI->connect("DBI:mysql:musicians_db", "musicfan", "CrimsonKing");

die "connect failed: " DBI->errstr() unless $dbh;

# use a table join to query the instrument names

407

my $sth = $dbh->prepare("SELECT musicians.name

FROM musicians,what_they_play,instruments

WHERE instruments.instrument = ? AND

musicians.player_id = what_they_play.player_id AND

what_they_play.inst_id = instruments.inst_id")

or die "prepare failed: " $dbh->errstr();

$sth->execute($instrument) or die "execute failed: " $sth->errstr();

# loop through them, printing them

while (($musician) = $sth->fetchrow()) {

start_html("Musicians who play $instrument");

h1("Musicians who play $instrument");

my $dbh = DBI->connect("DBI:mysql:musicians_db", "musicfan",

"CrimsonKing");

my $sth = $dbh->prepare("SELECT name

FROM musicians, what_they_play, instruments

WHERE instruments.instrument = ? AND

instruments.inst_id = what_they_play.inst_id AND

what_they_play.player_id = musicians.player_id")

or die "prepare failed: " $dbh->errstr();

$sth->execute($instrument) or die "execute failed: " $sth->errstr();

my($name);

while (($name) = $sth->fetchrow()) {

my $sth = $dbh->prepare("SELECT instrument FROM instruments")

or die "prepare failed: " $dbh->errstr();

$sth->execute() or die "execute failed: " $sth->errstr();

my($instrument);

while (($instrument) = $sth->fetchrow()) {

print qq{<option value="$instrument">$instrument</option>}; }

% percent sign, prefixing hashes, 115

< left angle bracket, indicating read mode, 180,

182

< less-than operator comparing numbers and, 29 comparing strings and, 35

<< operator, 20, 37

<> angle brackets, enclosing filehandles, 183

<> diamond See diamond

<= less-than-or-equal-to operator, 30, 71

<STDIN> (standard input), 49, 55, 67

> greater-than operator comparing numbers and, 29 comparing strings and, 35

> right angle bracket, indicating write mode,

& AND operator, 26

&& (and) operator, 31, 61

() parentheses See parentheses

* asterisk metacharacter, 165, 166, 167

subroutine declaration and, 136

? question mark metacharacter, 165, 166, 167

: colon, data sources and, 369

“ ” double quotes, for strings, 17

@ at sign, prefixing arrays, 91

@_, passing arguments to subroutines and,

137–142, 147–152

@ARGV array variable

command-line arguments and, 187

<=> spaceship operator, 30, 113

= assignment operator array assignments and, 91 multiple assignments and, 43 operator precedence and, 40 scalar assignments and, 38

=> operator, 36, 116

=~ operator, 37, 155, 158, 170

== comparison operator, 28, 56, 237 -> arrow notation, 241, 245, 289

0 prefix, 22 0x prefix, 22

■ A

\a escape sequence (alarm), 8 a() method, 331, 333

abstraction (encapsulation), 290, 293 accessing

arrays, 95–109 list values, 87–91 accessor methods, 302, 312 action at a distance, variables and, 146 action attribute, CGI programs and, 334, 338 ActivePerl

module installation and, 280 Win32 modules and, 276 addition operator (+), 23

and (&&) operator, 31, 61

AND operator (&), 26

angle brackets <>, enclosing filehandles, 183

default values for, 150

how they are passed, 147–152

named parameters and, 151

arithmetic operators, 23–25

array elements, references and, 238

array indexes (array subscripts), 97

exists() function and, 124

for loop and, 100

foreach loop and, 101, 103

tree-like data structures and, 250 variable interpolation and, 93 while loop and, 100

arrow notation (->), 241 matrices and, 245 methods and, 289 ASCII character set, 8 ASCII values, 34 assignable lists, 90 assignment operator (=) array assignments and, 91 multiple assignments and, 43 operator precedence and, 40 scalar assignments and, 38

associative arrays See hashes

asterisk (*) metacharacter, 165, 166, 167

at sign (@), prefixing arrays, 91 attributes, 288

classes and, 304–307, 312 providing, 300

storing, 298 audio, Win32::Sound and, 276 autoclosing files, 180

auto-decrement operator ( ), 41 auto-increment operator (++), 41 automatic conversion of scalars, 21, 34 autovivification, 245–249

base 10 (decimal system), 10

base 16 (hexadecimal system), 10

base 2 (binary system), 10

base 8 (octal system), 10

breaking out of loops/blocks, 74

browsers, CGI and, 317–348

DBI module and, 378–385 static vs dynamic, 336 troubleshooting, 320 writing, 318–325 character classes, 161–163 character sets (character encoding), 8 chdir() function, 221