Modern Perl for Non-Perl Programmers

Modern Perl for
Non-Perl
Programmers
Dave Cross
dave@mag-sol.com

Topics
●

What is Modern Perl?

●

Variables

●

Flow control

●

Subroutines

●

References

●

Context

London Perl Workshop
30th November 2013

Topics
●

CPAN

●

Useful Libraries
–
–

Database Access

–
●

Object Oriented Programming
Web Programming

Further Information

30th November 2013

What is Modern Perl
●

Not well defined

●

Can mean at least two things

●

Changes to core Perl syntax

●

Big additions to Perl's toolset
–
–

DBIx::Class

–
●

Moose
Catalyst

We will cover both

30th November 2013

Perl Releases
●

Annual release cycle
–

Usually in spring

●

Minor versions when required

●

Even major version is stable
–

●

5.10.x, 5.12.x, 5.14.x, 5.16.x, 5.18.x, etc

Odd major version is development
–

5.9.x, 5.11.x, 5.13.x, 5.15.x, 5.17.x, 5.19.x, etc

30th November 2013

Perl Support
●

Perl is maintained by volunteers

●

Support resource is limited

●

Official support for two major releases
–

●

Currently 5.16 and 5.18

Support for older releases may be available from
vendors

30th November 2013

Current Version
●

5.18.1
–

●

12 Aug 2013

5.20.0 due next spring
–

5.19.6

–

20 Nov 2013

30th November 2013

Introduction to Perl
●

Quick look at some Perl features

●

Differences from other languages

●

Variables

●

Flow control

●

Subroutines

●

Context

30th November 2013

Variables in Perl
●

Perl variables are of three kinds

●

Scalars

●

Arrays

●

Hashes

●

Filehandles and Subroutines can also be treated
like variables
–

But we won't be covering that today

30th November 2013

Perl Variable Types
●

Not the kind of data they store
–

String, Integer, Float, Boolean

●

The amount of data

●

How it is accessed

30th November 2013

Variable Names
●
●

●

Contain alphanumeric characters and underscores
User-defined variable names may not start with
numbers
Variable names are preceded by a punctuation
mark indicating the type of data

30th November 2013

Sigils
●

Punctuations marks indicate variable type

●

Scalars use $
–

●

Arrays use @
–

●

$doctor
@time_lords

Hashes use %
–

%companions

30th November 2013

Declaring variables
●

You don't need to declare variables

●

But it's a very good idea
–
–

●

●

●

Typos
Scoping

use strict enforces this
use strict;
my $doctor;
my ($doctor, @time_lords, %companions);

30th November 2013

Scalar Variables
●

●

●

Store a single item of data
my $name = "Arthur";
my $whoami =
'Just Another Perl Hacker';

●

my $meaning_of_life = 42;

●

my $number_less_than_1 = 0.000001;

●

my $very_large_number = 3.27e17;
# 3.27 times 10 to the power of 17

30th November 2013

Type Conversions
●

●
●

●
●

Perl converts between strings and numbers
whenever necessary
Add int to a floating point number
my $sum = $meaning_of_life +
$number_less_than_1;
Putting a number into a string
print "$name says, 'The meaning of
life is $sum.'n";

30th November 2013

Quoting Strings
●

●
●
●

Single quotes don't expand variables or escape
sequences
my $price = '$9.95';
Double quotes do
my $invline =
"24 widgets @ $price eachn";

30th November 2013

Backslashes
●

●

●

Use a backslash to escape special characters in
double quoted strings
print "He said "The price is
$300"";
This can look ugly

30th November 2013

Better Quotes
●
●

This is a tidier alternative
print qq(He said "The price is
$300");

●

Also works for single quotes
print q(He said "That's too
expensive");

●

Doesn't need to be brackets

●

30th November 2013

Choose Your Quotes
●

Choose characters to use with q() and qq()

●

Brackets
–
–

●

Close with opposite character
q(...), q[...], q{...}, q<...>

Non-brackets
–
–

●

Close with same character
q/.../, q|...|, q+...+, q#...#

Similar rules for many quote-like operators

30th November 2013

Undefined Values
●

A scalar that hasn't had data put into it will contain
the special value “undef”

●

Test for it with defined() function

●

if (defined($my_var)) { ... }

●

Like NULL in SQL

30th November 2013

Array Variables
●
●

Arrays contain an ordered list of scalar values
my @fruit = ('apples', 'oranges',
'guavas', 'passionfruit',
'grapes');

●

my @magic_numbers = (23, 42, 69);

●

Individual elements can be different types

●

my @random_scalars = ('mumble', 123.45,
'dave cross',
-300, $name);

30th November 2013

Array Elements
●
●

●
●

●

Accessing individual elements of an array
print $fruits[0];
# prints "apples"
Note: Indexes start from zero
print $random_scalars[2];
# prints "dave cross"
Note @ changes to $ when accessing single
elements

30th November 2013

Sigil Changes
●

Array sigil changes from @ to $

●

When accessing individual elements

●

Each element is a scalar

●

Therefore use scalar sigil

●

Similar in English
–

“These elements” vs “This element”

30th November 2013

Array Slices
●
●

●

●

Returns a list of elements from an array
print @fruits[0,2,4];
# prints "apples", "guavas",
# "grapes"
print @fruits[1 .. 3];
# prints "oranges", "guavas",
# "passionfruit"

Note use of @ as we are accessing more than one
element of the array
–

“These elements”

30th November 2013

Setting Array Values
●

$array[4] = 'something';

●

$array[400] = 'something else';

●

Also with slices
@array[4, 7 .. 9] =
('four','seven', 'eight','nine');

●

@array[1, 2] = @array[2, 1];

●

30th November 2013

Array Size
●

●

●

●

$#array is the index of the last element in
@array

Therefore $#array + 1 is the number of
elements
$count = @array;

Does the same thing and is easier to
understand

30th November 2013

Array vs List
●

Arrays and lists are different

●

Often confused

●

●

●
●

Array is a variable
– @array
List is a data literal
– (1, 2, 3, 4)
Like $scalar vs 'string'
Lists can be stored in arrays
– @array = (1, 2, 3, 4);

30th November 2013

Hash Variables
●

●
●

Hashes implement “look-up tables” or
“dictionaries”
Initialised with a list
%french = ('one', 'un',
'two', 'deux',
'three', 'trois');

30th November 2013

Fat Comma
●
●

The “fat comma” is easier to understand
%german = (one
=> 'ein',
two
=> 'zwei',
three => 'drei');

30th November 2013

Accessing Hash Values
●

$three = $french{three};

●

print $german{two};

●

Note sigil change

●

For exactly the same reason

30th November 2013

Hash Slices
●

Just like array slices

●

Returns a list of elements from a hash

●

●

print @french{'one','two','three'};
# prints "un", "deux" & "trois"

Strange sigil change
–

% becomes @

–

A list of values

30th November 2013

Setting Hash Values
●

$hash{foo} = 'something';

●

$hash{bar} = 'something else';

●
●

●

Also with slices
@hash{'foo', 'bar'} =
('something', 'else');
@hash{'foo', 'bar'} =
@hash{'bar', 'foo'};

30th November 2013

The Default Variable
●

●
●

●

Many Perl operations either set $_ or use its value
if no other is given
print; # prints the value of $_
If a piece of Perl code seems to be missing a
variable, then it's probably using $_
Think of “it” or “that” in English

30th November 2013

Using the Default Variable
●

●

while (<$file>) {
if (/regex/) {
print;
}
}
Three uses of $_
–

Input

–

Match

–

Print

30th November 2013

Flow Control
●

Perl has all the flow control features you'd expect

●

And some that you might not

●

Flow is controlled by Boolean logic

30th November 2013

Boolean Values in Perl
●

Perl has no Boolean data type

●

All scalar values are either true or false

●

Small set of false values
–

●

0, undef, empty string, empty list

Everything else is true

30th November 2013

Comparison Operators
●

Compare two values in some way

●

Are they equal
–
–

●

$x == $y or $x eq $y
$x != $y or $x ne $y

Is one greater than another
–

$x > $y or $x gt $y

–

$x >= $y or $x ge $y

30th November 2013

Two Sets of Operators
●

Remember Perl converts between types

●

Is “0” the same as “0.0”?
–
–

As a number it is
As a string it isn't

●

Programmer needs to tell Perl the kind of comparison to make

●

String
–

●

eq, ne, lt, le, gt, ge

Number
–

==, !=, <, <=, >, >=

30th November 2013

Comparison Examples
●

62 > 42

# true

●

'0' == (3 * 2) - 6

# true

●

'apple' gt 'banana' # false

●

'apple' == 'banana' # true(!)

●

1 + 2 == '3 bears'

# true

●

1 + 2 == 'three'

# false

30th November 2013

Boolean Operators
●

Combine conditional expressions

●

EXPR_1 and EXPR_2
true if both EXPR_1 and EXPR_2 are true
EXPR_1 or EXPR_2
–

●

–

true if either EXPR_1 or _EXPR_2 are true

●

Alternative syntax && for “and” and || for “or”

●

Different precedence though

30th November 2013

Short-Circuit Logic
●
●

●
●

●

EXPR_1 or EXPR_2
Only need to evaluate EXPR_2 if EXPR_1
evaluates as false
We can use this to make code easier to follow
open my $file, 'something.dat'
or die "Can't open file: $!";
@ARGV == 2 or print $usage_msg;

30th November 2013

Flow Control in Perl
●

Standard flow control statements
–
–

for

–
●

if/elsif/else
while

Some less standard ones
–

unless

–

foreach

–

until

30th November 2013

If / Else
●

●

if (EXPR) {
BLOCK
}
if (EXPR) {
BLOCK1
} else {
BLOCK2
}

30th November 2013

If / Else
●

●

if ($lives < 0) {
die “Game over”;
}
if ($lives < 0) {
} else {
print “You won!”;
}

30th November 2013

If / Elsif / Else
●

if (EXPR1) {
BLOCK1
} elsif (EXPR2) {
BLOCK2
} else {
BLOCK3
}

●

Note spelling of “elsif”

●

As many elsif clauses as you want

●

Else clause is optional

30th November 2013

If / Elsif / Else
●

if ($temp > 25) {
print “Too hot”;
} elsif ($temp < 10) {
print “Too cold”;
} else {
print “Just right”;
}

30th November 2013

For
●

●

C-style for loop
for ( INIT; EXPR; INCR ) {
BLOCK
}
–
–

If EXPR is false exit loop

–

Execute BLOCK and INCR

–
●

Execute INIT

Retry EXPR

Rarely used

30th November 2013

For
●

for ( $x = 0; $x <=10 ; ++$x ) {
print “$x squared is “, $x * $x;
}

30th November 2013

While
●
●

Execute loop while a condition is true
while (EXPR) {
BLOCK
}

30th November 2013

While
●

while ($continue) {
if (do_something_useful()) {
print $interesting_value;
} else {
$continue = 0;
}
}

30th November 2013

Unless
●

●

●

●

●

Inverted if
unless ( EXPR ) {
BLOCK
}
Exactly the same as
if ( ! EXPR ) {
BLOCK
}
Unless/else works
–

●

But is usually unhelpful

There is no elsunless

30th November 2013

Unless
●

unless ($lives) {
}

30th November 2013

Foreach
●

●

Iterate over a list
foreach VAR ( LIST ) {
BLOCK
}

●

For each element in LIST

●

Put element in VAR

●

Execute BLOCK

●

Often simpler than equivalent for loop

30th November 2013

Foreach
●

foreach my $x ( 1 .. 10 ) {
print “$x squared is “, $x * $x;
}

30th November 2013

Until
●
●

●
●

Inverted while
until ( EXPR ) {
BLOCK
}
Exactly the same as
while ( ! EXPR ) {
BLOCK
}

30th November 2013

Until
●

until ($stop) {
if (do_something_useful()) {
print $interesting_value;
} else {
$stop = 1;
}
}

30th November 2013

Common Usage
●
●

A while loop is often used to read from files
while (<$filehandle>) {
# Do stuff
}

●

Reads a record at a time

●

Stores the record in $_

30th November 2013

Statement Modifiers
●

Condition at end of statement

●

Invert logic

●

Can be more readable
–
–

print “Game over” unless $lives

–
●

help_text() if $option eq '-h'
print while <$filehandle>

Omit condition brackets

30th November 2013

Subroutines
●

Perl subroutines work much like other languages

●

Subroutines have a name and a block of code

●

Defined with the sub keyword

●

sub a_subroutine {
# do something useful
}

30th November 2013

Subroutine Arguments
●
●

Subroutine arguments end up in @_
sub do_stuff {
my ($arg1, $arg2) = @_;
# Do something with
# $arg1 and $arg2
}

●

Variable number of arguments

30th November 2013

Pass By Reference
●

●

Values in @_ are aliases to external variables
my $x = 10;
square($x);
print $x; # prints 100
sub square {
$_[0] = $_[0] * $_[0];
}

●

Usually not a good idea

30th November 2013

Pass By Value
●

●

●

Take copies of the arguments
Return changed values
my $x = 10;
my $sqr = square($x);
print $sqr; # prints 100
sub square {
my ($arg) = @_;
return $arg * $arg;
}

30th November 2013

Returning Values
●

●

●

Subroutines return a list
So it's simple to return a variable number of values
sub is_odd {
my @odds;
foreach (@_) {
push @odd, $_ if $_ % 2;
}
return @odds;
}

30th November 2013

Subroutine Variables
●

●

Variable can be scoped to within a subroutine
sub with_var {
my $count = 0; # scoped to sub
print ++$count; # always prints 0
}

●

Good practice

●

Variables are recreated each time subroutine is called

30th November 2013

Static Variables
●

●

●

Use state to declare variables that retain values
between calls
sub with_static_var {
state $count = 0; # scoped to
# sub
say ++$count; # increments on
# each call
}
Introduced in Perl 5.10.0

30th November 2013

Prototypes
●
●

You might see code with prototypes for subroutines
sub with_a_prototype ($$$) {
my ($foo, $bar, $baz) = @_;
...
}

●

Not like prototypes in other languages

●

Rarely necessary

●

Often confusing

30th November 2013

References
●

Sometimes arrays and hashes are hard to use

●

Need a reference to a variable

●

A bit like a pointer
–

But cleverer

–

A reference knows what type it is a reference to

●

Unique identifier to a variable

●

Always a scalar value

30th November 2013

Creating a Reference
●

Use to get a reference to a variable
–
–

●

my $arr_ref = @array
my $hash_ref = %hash

Or create an anonymous variable directly
–

my $arr_ref = [ 'foo', 'bar', 'baz' ]

–

my $hash_ref = { one => 1, two => 2 }

30th November 2013

Using References
●

Use -> to access elements from a reference
–
–

●

$arr_ref->[0]
$hash_ref->{one}

Use @ or % to get whole variable
–

@array = @$arr_ref

–

%hash = %$hash_ref

30th November 2013

Why Use References
●

●

●

●

Arrays and hashes are hard to pass as parameters to
subroutines
my_sub(@arr1, @arr2)
And then inside subroutine
my (@a1, @a2) = @_
–

Doesn't work

–

Arrays are flattened in @_

–

List assignment works against us

30th November 2013

Parameters as References
●
●
●
●

Take references instead
my_sub(@arr1, @arr2)
And then inside subroutine
my ($a1, $a2) = @_
–

Works as expected

–

Array references are scalar values

–

List assignment is tamed

30th November 2013

More References
●

Printing a reference is unhelpful
–
–

●

ARRAY(0xcce998)
HASH(0x2504998)

Use ref to see what type a reference is
–

ref [ 1, 2, 3 ]
●

–

ARRAY

ref { foo => 'bar' }
●

HASH

30th November 2013

Advanced References
●

Perl objects are usually implemented as hash
references
–

●

You can create references to subroutines
–

●

But they are “blessed”
my $sub_ref = &my_sub;
$sub_ref->('some', 'parameters');

Anonymous subroutines
–

my $sub_ref = sub { print “Boo” };
$sub_ref->();

30th November 2013

Context
●

●
●

Perl expressions can evaluate to different values
according to context
The way that they are evaluated
@arr = localtime
–

●

(56, 31, 15, 22, 8, 112, 6, 265, 1)

$scalar = localtime
–

Sat Sep 22 15:31:56 2012

30th November 2013

Scalar Context
●

Assignment to a scalar variable

●

Boolean expression
–

if (@arr) { ... }

●

Some built-in functions that take one parameter

●

Operands to most operators

●

Force scalar context with scalar
–

print scalar localtime

30th November 2013

List Context
●

List assignments
–
–

($x, $y, $z) = some_function()

–
●

@arr = some_function()
($x) = some_function()

Most built-in functions

30th November 2013

Subroutine Parameters
●
●

●

●

A common error
sub something {
my $arg = @_;
...
}
Should be
sub something {
my ($arg) = @_;
...
}

30th November 2013

Context Rules
●

There are no general rules

●

Need to learn

●

Or read documentation

30th November 2013

Mind Your Contexts
●

The difference can be hard to spot

●

print “Time: ”, localtime;

●

print “Time: ” . localtime;

●

Comma imposes list context

●

Concatenation imposes scalar context

30th November 2013

File Input Contexts
●

The file input operator handles different contexts

●

$line = <$filehandle>;

●

@lines = <$filehandle>;

●

($line) = <$filehandle>; # danger!

30th November 2013

CPAN
●
●
●

Comprehensive Perl Archive Network
Free Perl modules
Searchable
–

●

metacpan.org

Ecosystem of web sites
–
–
–
–
–

CPAN testers
cpanratings
Annocpan
CPAN deps
Many more...

30th November 2013

Installing CPAN Modules
●

Try your usual package repositories
–
–

apt-get

–
●

yum
ppm

May not have the modules you want
–

Or may have slightly older versions

30th November 2013

Installing CPAN Modules
●

Various command line tools
–
–

CPANPLUS (cpanp)

–
●

CPAN Shell (cpan)
CPANMinus (cpanm)

Install dependencies too

30th November 2013

Useful CPAN Libraries
●

Powerful CPAN modules

●

Object-Oriented Programming

●

Database access
–

●

Object Relational Mapping

Web Development
–

MVC frameworks

–

Server/application glue

30th November 2013

Object Oriented Programming
●

Perl has supported OOP since version 5.0
–

●

October 1994

Perl 5 OO sometimes described as appearing
“bolted on”

●

That's because it was bolted on

●

Powerful and flexible

●

Not particularly easy to understand

30th November 2013

Enter Moose
●

A complete modern object system for Perl 5

●

Based on experiments with Perl 6 object model

●

Built on top of Class::MOP
–
–

Set of abstractions for components of an object system

–
●

MOP - Meta Object Protocol
Classes, Objects, Methods, Attributes

An example might help

30th November 2013

Moose Example
●

package Point;
use Moose;
has 'x' => (isa
is
has 'y' => (isa
is

=>
=>
=>
=>

sub clear {
my $self = shift;
$self->x(0);
$self->y(0);
}

30th November 2013

'Int',
'rw');
'Int',
'rw');

Creating Attributes
●

has 'x' => (isa => 'Int',
is => 'rw')
–
–

Constrained to be an integer

–
●

Creates an attribute called 'x'
Read-write

has 'y' => (isa => 'Int',
is => 'rw')

30th November 2013

Defining Methods
●

●

sub clear {
my $self = shift;
$self->x(0);
$self->y(0);
}

First parameter is the object
–

●

Stored as a blessed hash reference

Uses generated methods to set x & y

30th November 2013

Subclassing
●

package Point3D;
use Moose;
extends 'Point';
has 'z' => (isa => 'Int', is => 'rw');
after 'clear' => sub {
my $self = shift;
$self->z(0);
};

30th November 2013

Subclassing
●

extends 'Point'
–

●

Define which class we're a subclass of

has 'z' => (
isa = 'Int', is => 'rw'
)
–

Adds new attribute 'z'

30th November 2013

Extending Methods
●

after 'clear' => sub {
my $self = shift;
$self->z(0);
};

●

New clear method for subclass

●

Called after method for superclass

30th November 2013

Using Moose Classes
●
●

●

Moose classes are used just like any other Perl class
$point = Point->new(x => 1,
y => 2);
say $point->x;
$p3d

= Point3D->new(x => 1,
y => 2,
z => 3);
$p3d->clear;

30th November 2013

More About Attributes
●

●

●

Use the has keyword to define your class's
attributes
has 'first_name' =>
( is => 'rw' );
Use is to define rw or ro

30th November 2013

Getting & Setting
●

●
●

●

By default each attribute creates a method of
the same name.
Used for both getting and setting the attribute
$dave->first_name('Dave');
say $dave->first_name;

30th November 2013

Required Attributes
●

By default Moose class attributes are optional

●

Change this with required

●

has 'name' => (
is
=> 'ro',
required => 1,
);

●

Forces constructor to expect a name

●

Although that name could be undef

30th November 2013

Attribute Defaults
●
●

●

●

Set a default value for an attribute with default
has 'size' => (
is
=> 'rw',
default
=> 'medium',
);
Can use a subroutine reference
has 'size' => (
is
=> 'rw',
default
=> &rand_size,
);

30th November 2013

More Attribute Properties
●

lazy
–

●

trigger
–

●

Subroutine called after the attribute is set

isa
–

●

Only populate attribute when queried

Set the type of an attribute

Many more

30th November 2013

More Moose
●
●
●

Many more options
Support for concepts like delegation and roles
Powerful plugin support
–

●

MooseX::*

Lots of work going on in this area

30th November 2013

Database Access
●

Perl has standard tools for accessing databases

●

DBI (Database Interface)
–

●

Standardised interface

DBD (Database Driver)
–

Specific support for particular database engine

30th November 2013

Good and Bad
●

Good
–
–

●

Standardised
Supports many databases

Bad
–

SQL

30th November 2013

Object Relational Mapping
●

Databases map well to OO

●

Tables are classes

●

Rows are objects

●

Columns are attributes

●

Not a new idea

30th November 2013

DBIx::Class
●

DBI extension

●

Define classes in Perl

●

We write Perl

●

DBIx::Class writes the SQL

30th November 2013

No More SQL
●
●

Old style
my $sql = 'update thing
set foo = “new foo”
where id = 10';
my $sth = $dbh->prepare($sql);
$sth->execute;

30th November 2013

No More SQL
●
●

New style
my $things =
$schema->resultset('Thing');
my $thing = $foo->find(10);
$thing->foo('new foo');
$thing->update;

30th November 2013

ORM Basics
●

Each class needs some information

●

The table it represents

●

The columns in that table

●

The types of those columns

●

Which column is the primary key

●

Which columns are foreign keys

30th November 2013

Sample Artist Class
●

package CD::Schema::Result::Artist;
use base qw/DBIx::Class::Core/;
__PACKAGE__->table('artist');
__PACKAGE__->add_columns(qw/ id name /);
__PACKAGE__->set_primary_key('id');
__PACKAGE__->has_many(cds =>
'CD::Schema::Result::CD', 'artist'
);
1;

30th November 2013

Sample CD Class
●

package CD::Schema::Result::CD;
use base qw/DBIx::Class::Core/;
__PACKAGE__->table('cd');
__PACKAGE__->add_columns(qw/ id artist
title year /);
__PACKAGE__->set_primary_key('cd');
__PACKAGE__->belongs_to(artist =>
'CD::Schema::Result::Artist', 'artist'
);
1;

30th November 2013

Sample Schema Class
●

package CD::Schema;
use base qw/DBIx::Class::Schema/;
__PACKAGE__->load_namespaces();
1;

30th November 2013

Listing Artists
●

use CD::Schema;
my $sch = CD::Schema->connect(
$dbi_dsn, $user, $pass
);
my $artists_rs =
$sch->resultset('Artist');
my @artists = $artists_rs->all;

30th November 2013

Listing Artists
●

foreach my $artist (@artists) {
say $artist->name;
foreach my $cd ($artist->cds) {
say “t”, $cd->title,
' (', $cd->year, ')';
}
}

30th November 2013

Searching Artists
●

●

my @davids = $artist_rs->search({
name => { like => 'David %' },
});
Powerful searching syntax

30th November 2013

Adding CD
●

my $bowie = $artist_rs->single({
name = 'David Bowie',
});
my $toy = $bowie->add_to_cds({
title => 'The Next Day',
year => 2013,
});

30th November 2013

Auto-Generating Schema
●

Writing schema classes is boring

●

Need to stay in step with database

●

Easy to make a mistake

●

Or to forget to update it

●

Auto-generate from database metadata

30th November 2013

ORM Basics
●

Each class needs some information

●

The table it represents

●

The columns in that table

●

The types of those columns

●

Which column is the primary key

●

Which columns are foreign keys

●

Database knows all of these

30th November 2013

DBIx::Class::Schema::Loader
●

Connects to database

●

Queries metadata

●

Generates class definitions

●

Writes them to disk

●

Command line program
–

dbicdump

30th November 2013

Schema Loader Example
●

CREATE DATABASE CD;
CREATE TABLE artist (
id INTEGER AUTO_INCREMENT NOT NULL PRIMARY KEY,
name VARCHAR(200)
) ENGINE=InnoDB;
CREATE TABLE cd (
id INTEGER AUTO_INCREMENT NOT NULL PRIMARY KEY,
artist INTEGER,
title VARCHAR(200),
year INTEGER,
FOREIGN KEY (artist) REFERENCES artist (id)
) ENGINE=InnoDB;

30th November 2013

Schema Loader Example
●

●

●

$ mysql -uuser -ppass -Dcd < cd.sql
$ dbicdump CD::Schema dbi:mysql:database=cd root ''
Dumping manual schema for CD::Schema to directory .
...
Schema dump completed.
$ find CD
CD
CD/Schema
CD/Schema/Result
CD/Schema/Result/Cd.pm
CD/Schema/Result/Artist.pm
CD/Schema.pm

30th November 2013

Web Development
●

Writing a web application is always harder than
you think it will be

●

A good framework makes things easier

●

Takes care of the boring things
–

Authentication/Authorisation

–

Session management

–

Logging

–

Etc...

30th November 2013

Perl Web Frameworks
●

Plenty to choose from on CPAN

●

Web::Simple
–

●

Dancer
–

●

Lightweight and flexible

Mojolicious
–

●

Simple to install and use

“Next Generation Web Framework”

Catalyst
–

Extremely powerful

30th November 2013

Building on Existing Tools
●

Frameworks build on existing tools

●

Template Toolkit
–

Generating HTML

●

DBIx::Class

●

Moose

●

Not mandatory
–

Not opinionated software

30th November 2013

Dancer
●

●

Route-based framework
use Dancer;
get '/' => sub {
return 'Hello World”;
};
dance;

●

bin/app.pl

30th November 2013

Catalyst
●

MVC framework
–

Model, View, Controller

●

Most popular Perl web framework

●

Powerful

●

Flexible

30th November 2013

PSGI & Plack
●

PSGI is the future of Perl web development
–

But it's here now

●

PSGI is a protocol specification

●

Plack is a toolkit

30th November 2013

What's the Problem?
●

Web apps run in many environments

●

CGI

●

mod_perl handler

●

FCGI

●

Etc...

●

All have different interfaces

30th November 2013

What's the Problem?
●
●

●

There are many Perl web frameworks
They all need to support all of the web
environments
Duplication of effort
–

Catalyst supports mod_perl

–

Dancer supports mod_perl

–

Web::Simple supports mod_perl

–

Etc...

30th November 2013

PSGI
●
●

Perl Server Gateway Interface
Defines interaction between web application and
web server

●

A bit like CGI

●

A lot like WSGI

30th November 2013

What's the Advantage?
●

Web frameworks only support PSGI interface

●

One PSGI interface per web environment

●

Less duplication of effort

●

Bonus

●

Easily portable code

30th November 2013

Other Advantages
●

Standardised development servers

●

Easier testing

●

Middleware

30th November 2013

PSGI Definition
●

A PSGI application is

●

A reference to a subroutine

●

Input is a hash
–

●

Actually a hash reference

Output is a three-element array
–

HTTP status code

–

Headers

–

Body

30th November 2013

Reference to Subroutine
●

my $app = sub {
my $env = shift;
return [
200,
[ ‘Content-Type’,‘text/plain’ ],
[ ‘Hello World’ ],
];
};

30th November 2013

Hash Reference
●

my $app = sub {
my $env = shift;
return [
200,
];
};

30th November 2013

Return Array Reference
●

my $app = sub {
my $env = shift;
return [
200,
];
};

30th November 2013

Plack
●
●

PSGI is just a specification
Plack is a bundle of tools for working with that
specification
–
–

●

Available from CPAN
A lot like Rack

Many useful modules and programs

30th November 2013

plackup
●
●

Test PSGI server
$ plackup app.psgi
HTTP::Server::PSGI: Accepting connections at
http://localhost:5000/

30th November 2013

Middleware
●

Middleware wraps around an application

●

Returns another PSGI application

●

Simple spec makes this easy

●

Plack::Middleware::*

●

Plack::Builder adds middleware configuration
language

30th November 2013

Middleware Example
●

use Plack::Builder;
use Plack::Middleware::Runtime;
my $app = sub {
my $env = shift;
return [
200,
[ 'Content-type', 'text/plain' ],
[ 'Hello world' ],
]
};
builder {
enable 'Runtime';
$app;
}

30th November 2013

Middleware Example
●

$ HEAD http://localhost:5000
200 OK
Date: Tue, 20 Jul 2010 20:25:52 GMT
Server: HTTP::Server::PSGI
Content-Length: 11
Content-Type: text/plain
Client-Date: Tue, 20 Jul 2010 20:25:52 GMT
Client-Peer: 127.0.0.1:5000
Client-Response-Num: 1
X-Runtime: 0.000050

30th November 2013

Plack::App::*
●

Ready-made solutions for common situations

●

Plack::App::CGIBin
–

●

Plack::App::Directory
–

●

cgi-bin replacement
Serve files with directory index

Plack::App::URLMap
–

Map apps to different paths

30th November 2013

Application Example
●

use Plack::App::CGIBin;
use Plack::Builder;
my $app = Plack::App::CGIBin->new(
root => '/var/www/cgi-bin'
)->to_app;
builder {
mount '/cgi-bin' => $app;
};

30th November 2013

Framework Support
●

●

●

Most modern Perl frameworks already support
PSGI
Catalyst, CGI::Application, Dancer, Jifty, Mason,
Maypole, Mojolicious, Squatting, Web::Simple
Many more

30th November 2013

PSGI Server Support
●

nginx support

●

mod_psgi

●

Plack::Handler::Apache2

30th November 2013

PSGI Server Support
●
●

●

Many new web servers support PSGI
Starman, Starlet, Twiggy, Corona,
HTTP::Server::Simple::PSGI
Perlbal::Plugin::PSGI

30th November 2013

PSGI/Plack Summary
●

PSGI is a specification

●

Plack is an implementation

●

PSGI makes your life easier

●

●

Most of the frameworks and servers you use
already support PSGI
No excuse not to use it

30th November 2013

Further Information
●

Very high-level overview

●

Lots of information available
–

Perl documentation

–

Books

–

Web sites

–

Mailing lists

–

User groups

–

Conferences

30th November 2013

Perl Documentation
●

Perl comes with a huge documentation set

●

Access it via “perldoc”

●

perldoc perl

●

perldoc perltoc

●

perldoc perlfaq

●

perldoc perldoc

30th November 2013

Perldoc Options
●

Documentation for a particular function
–

●

Documentation for a particular variable
–

●

perldoc -f print
perldoc -v @_

Search the FAQ for a keyword
–

perldoc -q sort

30th November 2013

Perl Books
●

Essential Perl books

●

Learning Perl (6ed)
–

●

Programming Perl (4ed)
–

●

Schwartz, Phoenix and foy
Wall, Christiansen, Orwant and foy

Perl Best Practices
–

Damian Conway

30th November 2013

Perl Books
●

Effective Perl Programming
–

●

Intermediate Perl (2ed)
–

●

Hall, McAdams and foy
Schwartz, foy and Phoenix

Mastering Perl
–

brian d foy

30th November 2013

Perl Books
●

Beginning Perl
–

●

Curtis Poe

Perl Testing – A Developers Notebook
–

Langworth, chromatic

30th November 2013

Perl Books
●

Modern Perl
–

●

chromatic

Definitive Guide to Catalyst
–

Diment, Trout

30th November 2013

Perl Web Sites
●

Perl home page
–

●

Perl documentation
–

●

www.perl.org
perldoc.perl.org

CPAN
–

metacpan.org

30th November 2013

Perl Web Sites
●

Perl News
–

●

perlnews.org

Perl Blogs
–
–

●

blogs.perl.org
ironman.enlightenedperl.org

Perl Foundation
–

perlfoundation.org

30th November 2013

Perl Web Sites
●

Perl User Groups (Perl Mongers)
–

●

www.pm.org

Perl Help
–
–

●

perlmonks.org
stackoverflow.com/questions/tagged/perl

Perl Tutorials
–

perl-tutorial.org

30th November 2013

Perl Mailing Lists
●

Dozens of lists
–

●

lists.perl.org

Perl Weekly
–

perlweekly.com

30th November 2013

Perl User Groups
●

Perl user groups are called “Perl Mongers”

●

Hundreds of groups worldwide
–

●

www.pm.org

London.pm one of the largest groups
–

london.pm.org

●

Monthly social meetings

●

Bi-monthly (ish) technical meetings

●

Mailing list

30th November 2013

Perl Conferences
●

OSCON (Open Source Convention)
–
–

●

Originally The Perl Conference
20 – 24 July 2014, Portland OR

YAPC (Yet Another Perl Conference)
–

23 – 25 June 2014, Orlando FL

–

August 2014, Sofia, Bulgaria

30th November 2013

Perl Workshops
●

Low cost (free)

●

One-day

●

Many cities all over the world

●

–

londonperlworkshop.org.uk

–

Nov/Dec

30th November 2013

The End
●

Thank you for coming

●

Hope you enjoyed it

●

Hope it was useful

●

Any questions?

30th November 2013

30th November 2013

Modern Perl for Non-Perl Programmers

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