1.
Introduction to Perl Day 2 An Introduction to Perl Programming Dave Cross Magnum Solutions Ltd [email_address]

2.
What We Will Cover <ul><li>Types of variable

3.
Strict and warnings

4.
References

5.
Sorting

6.
Reusable Code

7.
Object Orientation </li></ul>

8.
What We Will Cover <ul><li>Testing

9.
Dates and Times

10.
Templates

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Databases

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Further Information </li></ul>

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Schedule <ul><li>09:30 – Begin

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11:00 – Coffee break (30 mins)

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13:00 – Lunch (90 mins)

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14:30 – Begin

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16:00 – Coffee break (30 mins)

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18:00 – End </li></ul>

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Resources <ul><li>Slides available on-line </li><ul><li>http://mag-sol.com/train/public/2009/yapc </li></ul><li>Also see Slideshare </li><ul><li>http://www.slideshare.net/davorg/slideshows </li></ul><li>Get Satisfaction </li><ul><li>http://getsatisfaction.com/magnum </li></ul></ul>

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Types of Variable

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Types of Variable <ul><li>Perl variables are of two types

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Important to know the difference

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Lexical variables are created with my

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Package variables are created by our

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Lexical variables are associated with a code block

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Package variables are associated with a package </li></ul>

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Lexical Variables <ul><li>Created with my

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my ($doctor, @timelords, %home_planets);

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Live in a pad (associated with a block of code) </li><ul><li>Piece of code delimited by braces

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Source file </li></ul><li>Only visible within enclosing block

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&quot;Lexical&quot; because the scope is defined purely by the text </li></ul>

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Packages <ul><li>All Perl code is associated with a package

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A new package is created with package </li><ul><li>package MyPackage; </li></ul><li>Think of it as a namespace

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Used to avoid name clashes with libraries

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Default package is called main </li></ul>

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Package Variables <ul><li>Live in a package's symbol table

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Can be referred to using a fully qualified name </li><ul><li>$main::doctor

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@Gallifrey::timelords </li></ul><li>Package name not required within own package

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Can be seen from anywhere in the package (or anywhere at all when fully qualified) </li></ul>

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Declaring Package Vars <ul><li>Can be predeclared with our

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our ($doctor, @timelords, %home_planet);

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Or (in older Perls) with use vars

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use vars qw($doctor @timelords %home_planet); </li></ul>

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Lexical or Package <ul><li>When to use lexical variables or package variables?

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Simple answer </li><ul><li>Always use lexical variables </li></ul><li>More complete answer </li><ul><li>Always use lexical variables

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Except for a tiny number of cases </li></ul><li>http://perl.plover.com/local.html </li></ul>

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local <ul><li>You might see code that uses local

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local $variable;

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This doesn't do what you think it does

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Badly named function

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Doesn't create local variables

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Creates a local copy of a package variable

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Can be useful </li><ul><li>In a small number of cases </li></ul></ul>

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local Example <ul><li>$/ is a package variable

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It defines the record separator

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You might want to change it

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Always localise changes

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{ local $/ = “”; while (<FILE> ) { ... } } </li></ul>

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Strict and Warnings

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Coding Safety Net <ul><li>Perl can be a very loose programming language

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Two features can minimise the dangers

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use strict / use warnings

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A good habit to get into

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No serious Perl programmer codes without them </li></ul>

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use strict <ul><li>Controls three things

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use strict 'refs' – no symbolic references

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use strict 'subs' – no barewords

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use strict 'vars' – no undeclared variables

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use strict – turn on all three at once

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turn them off (carefully) with no strict </li></ul>

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use strict 'refs' <ul><li>Prevents symbolic references

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aka &quot;using a variable as another variable's name&quot;

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$what = 'dalek'; $$what = 'Karn'; # sets $dalek to 'Karn'

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What if 'dalek' came from user input?

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People often think this is a cool feature

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It isn't </li></ul>

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use strict 'refs' (cont) <ul><li>Better to use a hash

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$what = 'dalek'; $alien{$what} = 'Karn';

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Self contained namespace

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Less chance of clashes

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More information (e.g. all keys) </li></ul>

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use strict 'subs' <ul><li>No barewords

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Bareword is a word with no other interpretation

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e.g. word without $, @, %, &

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Treated as a function call or a quoted string

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$dalek = Karn;

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May clash with future reserved words </li></ul>

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use strict 'vars' <ul><li>Forces predeclaration of variable names

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Prevents typos

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Less like BASIC - more like Ada

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Thinking about scope is good </li></ul>

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use warnings <ul><li>Warns against dubious programming habits

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Some typical warnings </li><ul><li>Variables used only once

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Using undefined variables

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Writing to read-only file handles

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And many more... </li></ul></ul>

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Allowing Warnings <ul><li>Sometimes it's too much work to make code warnings clean

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Turn off use warnings locally

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Turn off specific warnings

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{ no warnings 'deprecated'; # dodgy code ... }

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See perldoc perllexwarn </li></ul>

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References

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Introducing References <ul><li>A reference is a bit like pointer in languages like C and Pascal (but better)

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A reference is a unique way to refer to a variable.

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A reference can always fit into a scalar variable

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A reference looks like SCALAR(0x20026730) </li></ul>

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Creating References <ul><li>Put in front of a variable name </li><ul><li>$scalar_ref = scalar;

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$array_ref = array;

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$hash_ref = hash; </li></ul><li>Can now treat it just like any other scalar </li><ul><li>$var = $scalar_ref;

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$refs[0] = $array_ref;

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$another_ref = $refs[0]; </li></ul></ul>

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Creating References <ul><li>[ LIST ] creates anonymous array and returns a reference

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$aref = [ 'this', 'is', 'a', 'list']; $aref2 = [ @array ];

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{ LIST } creates anonymous hash and returns a reference

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$href = { 1 => 'one', 2 => 'two' }; $href = { %hash }; </li></ul>

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Creating References <ul><li>@arr = (1, 2, 3, 4); $aref1 = arr; $aref2 = [ @arr ]; print &quot;$aref1$aref2&quot;;

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Output ARRAY(0x20026800) ARRAY(0x2002bc00)

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Second method creates a copy of the array </li></ul>

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Using Array References <ul><li>Use {$aref} to get back an array that you have a reference to

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Whole array

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@array = @{$aref};

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@rev = reverse @{$aref};

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Single elements

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$elem = ${$aref}[0];

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${$aref}[0] = 'foo'; </li></ul>

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Using Hash References <ul><li>Use {$href} to get back a hash that you have a reference to

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Whole hash

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%hash = %{$href};

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@keys = keys %{$href};

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Single elements

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$elem = ${$href}{key};

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${$href}{key} = 'foo'; </li></ul>

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Using References <ul><li>Use arrow ( -> ) to access elements of arrays or hashes

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Instead of ${$aref}[0] you can use $aref->[0]

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Instead of ${$href}{key} you can use $href->{key} </li></ul>

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Using References <ul><li>You can find out what a reference is referring to using ref

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$aref = [ 1, 2, 3 ]; print ref $aref; # prints ARRAY

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$href = { 1 => 'one', 2 => 'two' }; print ref $href; # prints HASH </li></ul>

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Why Use References? <ul><li>Parameter passing

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Complex data structures </li></ul>

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Parameter Passing <ul><li>What does this do?

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@arr1 = (1, 2, 3); @arr2 = (4, 5, 6); check_size(@arr1, @arr2); sub check_size { my (@a1, @a2) = @_; print @a1 == @a2 ? 'Yes' : 'No'; } </li></ul>

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Why Doesn't It Work? <ul><li>my (@a1, @a2) = @_;

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Arrays are combined in @_

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All elements end up in @a1

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How do we fix it?

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Pass references to the arrays </li></ul>

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Another Attempt <ul><li>@arr1 = (1, 2, 3); @arr2 = (4, 5, 6); check_size(arr1, arr2); sub check_size { my ($a1, $a2) = @_; print @$a1 == @$a2 ? 'Yes' : 'No'; } </li></ul>

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Complex Data Structures <ul><li>Another good use for references

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Try to create a 2-D array

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@arr_2d = ((1, 2, 3), (4, 5, 6), (7, 8, 9));

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@arr_2d contains (1, 2, 3, 4, 5, 6, 7, 8, 9)

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This is known a array flattening </li></ul>

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Complex Data Structures <ul><li>2D Array using references

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@arr_2d = ([1, 2, 3], [4, 5, 6], [7, 8, 9]);

156.
But how do you access individual elements?

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$arr_2d[1] is ref to array (4, 5, 6)

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$arr_2d[1]->[1] is element 5 </li></ul>

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Complex Data Structures <ul><li>Another 2D Array

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$arr_2d = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];

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$arr_2d->[1] is ref to array (4, 5, 6)

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$arr_2d->[1]->[1] is element 5

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Can omit intermediate arrows

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$arr_2d->[1][1] </li></ul>

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More Data Structures <ul><li>Imagine the following data file

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Jones,Martha,UNIT Harkness,Jack,Torchwood Smith,Sarah Jane,Journalist

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What would be a good data structure?

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Hash for each record

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Array of records

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Array of hashes </li></ul>

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More Data Structures <ul><li>Building an array of hashes

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my @records; my @cols = ('s_name', 'f_name', 'job'); while (<FILE>) { chomp; my %rec; @rec{@cols} = split /,/; push @records, rec; } </li></ul>

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Using an Array of Hashes foreach (@records) { print &quot;$_->{f_name} &quot;, &quot;$_->{s_name} &quot;. &quot;is a $_->{job}&quot;; }

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Complex Data Structures <ul><li>Many more possibilities </li><ul><li>Hash of hashes

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Hash of lists

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Multiple levels (list of hash of hash, etc.) </li></ul><li>Lots of examples in “perldoc perldsc” (the data structures cookbook) </li></ul>

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Sorting

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Sorting <ul><li>Perl has a sort function that takes a list and sorts it

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@sorted = sort @array;

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Note that it does not sort the list in place

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@array = sort @array; </li></ul>

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Sort Order <ul><li>The default sort order is ASCII

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@chars = sort 'e', 'b', 'a', 'd', 'c'; # @chars has ('a', 'b', 'c', 'd', 'e')

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This can sometimes give strange results

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@chars = sort 'E', 'b', 'a', 'D', 'c'; # @chars has ('D', 'E', 'a', 'b', 'c')

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@nums = sort 1 .. 10; # @nums has (1, 10, 2, 3, 4, # 5, 6, 7, 8, 9) </li></ul>

187.
Sorting Blocks <ul><li>Can add a &quot;sorting block&quot; to customise sort order

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@nums = sort { $a <=> $b } 1 .. 10;

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Perl puts two of the values from the list into $a and $b

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Block compares values and returns -1, 0 or 1

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<=> does this for numbers ( cmp for strings) </li></ul>

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Sort Examples <ul><li>Other simple sort examples

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sort { $b cmp $a } @words

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sort { lc $a cmp lc $b } @words

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sort { substr($a, 4) cmp substr($b, 4) } @lines </li></ul>

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Sorting Subroutines <ul><li>Can also use a subroutine name in place of a code block

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@words = sort dictionary @words; sub dictionary { # Don't change $a and $b my ($A, $B) = ($a, $b); $A =~ s/+//g; $B =~ s/+//g; $A cmp $B; } </li></ul>

198.
Sorting Names <ul><li>my @names = ('Rose Tyler', 'Martha Jones', 'Donna Noble', 'Amy Pond'); @names = sort sort_names @names;

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Need to write sort_names so that it sorts on surname and then forename. </li></ul>

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Sorting Names (cont) <ul><li>sub sort_names { my @a = split //, $a; my @b = split //, $b; return $a[1] cmp $b[1] or $a[0] cmp $b[1]; } </li></ul>

201.
More Complex Sorts <ul><li>sub sort_names { my @a = split //, $a; my @b = split //, $b; return $a[1] cmp $b[1] or $a[0] cmp $b[0]; }

202.
Can be inefficient on large amounts of data

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Multiple splits on the same data </li></ul>

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More Efficient Sorts <ul><li>Split each row only once

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@split = map { [ split ] } @names;

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Do the comparison

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@sort = sort { $a->[1] cmp $b->[1] or $a->[0] cmp $b->[0] } @split;

208.
Join the data together

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@names = map { join ' ', @$_ } @sort; </li></ul>

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Put It All Together <ul><li>Can rewrite this as

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@names = map { join ' ', @$_ } sort { $a->[1] cmp $b->[1] || $a->[0] cmp $b->[0] } map { [ split ] } @names;

212.
All functions work on the output from the previous function in the chain </li></ul>

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Schwartzian Transform <ul><li>@data_out = map { $_->[1] } sort { $a->[0] cmp $a->[0] } map { [func($_), $_] } @data_in;

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Old Lisp trick

215.
Named after Randal Schwartz </li></ul>

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Reusable Code

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Why Write Modules? <ul><li>Code reuse

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Prevent reinventing the wheel

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Easier to share across projects

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Better design, more generic </li></ul>

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Basic Module <ul><li>use strict; use warnings; package MyModule; use Exporter; our @ISA = ('Exporter'); our @EXPORT = ('my_sub'); sub my_sub { print &quot;This is my_sub&quot;; } 1; </li></ul>

222.
Using MyModule.pm <ul><li>use MyModule; # my_sub is now available # for use within your # program my_sub(); # Prints &quot;This is my_sub()&quot; </li></ul>

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Explaining MyModule.pm <ul><li>Much of MyModule.pm is concerned with exporting subroutine names

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Subroutine full name </li><ul><li>MyModule::my_sub() </li></ul><li>Exporting abbreviates that </li><ul><li>my_sub() </li></ul></ul>

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Packages Revisited <ul><li>Every subroutine lives in a package

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The default package is main

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New packages are introduced with the package keyword

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A subroutine's full name is package::name

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Package name can be omitted from within same package

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Like family names </li></ul>

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Using Exporter <ul><li>The module Exporter.pm handles the export of subroutine (and variable) names

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Exporter.pm defines a subroutine called import

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import is automatically called whenever a module is used

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import puts references to our subroutines into our caller's symbol table </li></ul>

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How Exporter Works <ul><li>How does MyModule use Exporter's import subroutine?

236.
We make use of inheritance

237.
Inheritance is defined using the @ISA array

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If we call a subroutine that doesn't exist in our module, then the modules in @ISA are also checked

239.
Therefore Exporter::import is called </li></ul>

240.
Exporting Symbols <ul><li>How does import know which subroutines to export?

241.
Exports are defined in @EXPORT or @EXPORT_OK

242.
Automatic exports are defined in @EXPORT

243.
Optional exports are defined in @EXPORT_OK </li></ul>

244.
Exporting Symbol Sets <ul><li>You can define sets of exports in %EXPORT_TAGS

245.
Key is set name

246.
Value is reference to an array of names

247.
our %EXPORT_TAGS = (advanced => [ qw( my_sub my_other_sub ) ]; use MyModule qw(:advanced); my_sub(); my_other_sub(); </li></ul>

248.
Why Use @EXPORT_OK? <ul><li>Give your users the choice of which subroutines to import

249.
Less chances of name clashes

250.
Use @EXPORT_OK in preference to @EXPORT

251.
Document the exported names and sets </li></ul>

252.
Exporting Variables <ul><li>You can also export variables

253.
@EXPORT_OK = qw($scalar, @array, %hash);

254.
Can be part of export sets

255.
Any variables you export must be package variables </li></ul>

256.
Writing Modules The Easy Way <ul><li>A lot of module code is similar

257.
Don't write the boilerplate yourself

258.
Copy from an existing module

259.
Or look at Module::Starter </li></ul>

260.
Object Orientation

261.
OO Programming <ul><li>Traditional programming has subroutines acting on methods

262.
OO inverts this

263.
Classes contain methods which define their actions

264.
Objects are instances of classes

265.
Perl has an OO system bolted on

266.
Best of both worlds </li></ul>

267.
Object Oriented Perl <ul><li>An Object is just a module that obeys certain extra rules

268.
Three rules of Perl objects </li><ul><li>A Class is a package

269.
An Object is a reference (usually to a hash)

270.
A Method is a subroutine </li></ul><li>bless tells a reference what kind of object it is </li></ul>

271.
A Simple Object <ul><li>package MyObject; sub new { my $class = shift; my $name = shift; my $self = { name => $name }; return bless $self, $class; } </li></ul>

272.
A Simple Object (cont) <ul><li>sub get_name { my $self = shift; return $self->{name}; } sub set_name { my $self = shift; $self->{name} = shift; } 1; </li></ul>

273.
Using MyObject.pm <ul><li>use MyObject; my $obj = MyObject->new('Dave'); print $obj->get_name; # prints 'Dave' $obj->set_name('David'); print $obj->get_name; # prints 'David' </li></ul>

274.
Moose <ul><li>Easier OO Perl

275.
Moose is on CPAN

276.
Based on Perl 6 OO

277.
Well worth investigating </li></ul>

278.
Moose Example <ul><li>package MyModule; use Moose; has name => (is => 'rw', isa => 'Str', required => 1);

279.
1; </li></ul>

280.
Further Information <ul><li>perldoc perlboot

281.
perldoc perltoot

282.
perldoc perlobj

283.
perldoc perlbot

284.
perldoc Moose (if it is installed)

285.
Object Oriented Perl (Conway) </li></ul>

286.
Testing

287.
Testing <ul><li>Never program without a safety net

288.
Does your code do what it is supposed to do?

289.
Will your code continue to do what it is supposed to do?

290.
Write unit tests

291.
Run those tests all the time </li></ul>

292.
When to Run Tests <ul><li>As often as possible

293.
Before you add a feature

294.
After you have added a feature

295.
Before checking in code

296.
Before releasing code

297.
Constantly, automaticall y </li></ul>

298.
Testing in Perl <ul><li>Perl makes it easy to write test suites

299.
A lot of work in this area over the last eight years

300.
Test::Simple and Test::More included in Perl distribution

301.
Many more testing modules on CPAN </li></ul>

302.
Simple Test Program <ul><li>use Test::More tests => 4; BEGIN { use_ok('My::Object'); } ok(my $obj = My::Object->new); isa_ok($obj, 'My::Object'); $obj->set_foo('Foo'); is($obj->get_foo, 'Foo'); </li></ul>

303.
Simple Test Output <ul><li>$ prove -v test.t test.... 1..4 ok 1 - use My::Object; ok 2 ok 3 - The object isa My::Object ok 4 ok All tests successful. Files=1, Tests=4, 0 wallclock secs ( 0.02 usr 0.00 sys + 0.05 cusr 0.00 csys = 0.07 CPU) Result: PASS </li></ul>

304.
Adding Test Names <ul><li>use Test::More tests => 4; BEGIN { use_ok('My::Object'); } ok(my $obj = My::Object->new, 'Got an object'); isa_ok($obj, 'My::Object'); $obj->set_foo('Foo'); is($obj->get_foo, 'Foo', 'The foo is &quot;Foo&quot;'); </li></ul>

305.
Output With Names <ul><li>$ prove -v test2.t test2.... 1..4 ok 1 - use My::Object; ok 2 - got an object ok 3 - The object isa My::Object ok 4 - The foo is &quot;Foo&quot; ok All tests successful. Files=1, Tests=4, 0 wallclock secs ( 0.02 usr 0.00 sys + 0.05 cusr 0.00 csys = 0.07 CPU) Result: PASS </li></ul>

306.
Using prove <ul><li>prove is a command line tool for running tests

307.
Runs given tests using Test::Harness

308.
Comes with the Perl distribution

309.
Command line options </li><ul><li>-v verbose output

310.
-r recurse

311.
-s shuffle tests

312.
Many more </li></ul></ul>

313.
Test Anything Protocol <ul><li>Perl tests have been spitting out “ok 1” and not “ok 2” for years

314.
Now this ad-hoc format has a definition and a name

315.
The Test Anything Protocol (TAP)

316.
See Test::Harness::TAP (documentation module) and TAP::Parser </li></ul>

317.
TAP Output <ul><li>More possibilities for test output </li><ul><li>TAP::Harness::Color

318.
Test::TAP::HTMLMatrix </li></ul><li>Make sense of your test results </li></ul>

319.
More Testing Modules <ul><li>Dozens of testing modules on CPAN

320.
Some of my favourites

321.
Test::File

322.
Test::Exception, Test::Warn

323.
Test::Differences

324.
Test::XML (includes Test::XML::XPath) </li></ul>

325.
Writing Test Modules <ul><li>These test modules all work together

326.
Built using Test::Builder

327.
Ensures that test modules all use the same framework

328.
Use it as the basis of your own Test::* modules

329.
Who tests the testers?

330.
Test your Test::Builder test modules with Test::Builder::Tester </li></ul>

331.
How Good Are Your Tests? <ul><li>How much of your code is exercised by your tests?

332.
Devel::Cover can help you to find out

333.
Deep internal magic

334.
Draws pretty charts </li><ul><li>HARNESS_PERL_SWITCHES= -MDevel::Cover make test

335.
cover </li></ul></ul>

336.
Devel::Cover Output

337.
Devel::Cover Output

338.
Devel::Cover Output

339.
Alternative Test Paradigms <ul><li>Not everyone likes the Perl testing framework

340.
Other frameworks are available

341.
Test::Class </li><ul><li>xUnit style framework </li></ul><li>Test::FIT </li><ul><li>Framework for Interactive Testing

342.
http://fit.c2.com </li></ul></ul>

343.
More Information <ul><li>Perl Testing: A Developer's Notebook (Ian Langworth & chromatic)

344.
perldoc Test::Tutorial

345.
perldoc Test::Simple

346.
perldoc Test::More

347.
perldoc Test::Builder

348.
etc... </li></ul>

349.
Dates and Times

350.
Dates & Times <ul><li>Perl has built-in functions to handle dates and times

351.
Flexible but confusing

352.
time – seconds since 1st Jan 1970

353.
localtime – convert to human-readable

354.
timelocal (in Time::Local) – inverse of localtime

355.
strftime (in POSIX) – formatting dates and times </li></ul>

356.
Dates & Times on CPAN <ul><li>Look to CPAN for a better answer

357.
Dozens of date/time modules on CPAN

358.
Date::Manip is almost never what you want

359.
Date::Calc, Date::Parse, Class::Date, Date::Simple, etc

360.
Which one do you choose? </li></ul>

361.
Perl DateTime Project <ul><li>http://datetime.perl.org/

362.
&quot;The DateTime family of modules present a unified way to handle dates and times in Perl&quot;

363.
&quot;unified&quot; is good

364.
Dozens of modules that work together in a consistent fashion </li></ul>

365.
Using DateTime <ul><li>use DateTime; my $dt = DateTime->now; say $dt; # 2009-08-02T15:06:07 say $dt->dmy, &quot;&quot;; # 2009-08-02 say $dt->hms, &quot;&quot;; # 15:06:07 </li></ul>

366.
Using DateTime <ul><li>use DateTime; my $dt = DateTime->new(year => 2009, month => 8, day => 2); say $dt->ymd('/'), &quot;&quot;; # 2009/08/02 say $dt->month; # 8 say $dt->month_name; # August </li></ul>

367.
Arithmetic <ul><li>A DateTime object is a point in time

368.
For date arithmetic you need a duration

369.
Number of years, weeks, days, etc </li></ul>

370.
Arithmetic <ul><li>use DateTime; my $dt = DateTime->new(year => 2009, month => 8, day => 2); my $two_weeks = DateTime::Duration->new(weeks => 2); $dt += $two_weeks; say $dt; # 2009-02-16T00:00:00 </li></ul>

371.
Formatting Output <ul><li>use DateTime; my $dt = DateTime->new(year => 2009, month => 2, day => 26); say $dt->strftime('%A, %d %B %Y'); # Tuesday, 26 February 2009

372.
Control input format with DateTime::Format::Strptime </li></ul>

373.
Parsing & Formatting <ul><li>Ready made parsers and formatters for popular date and time formats

374.
DateTime::Format::HTTP

375.
DateTime::Format::MySQL

376.
DateTime::Format::Excel

377.
DateTime::Format::Baby </li><ul><li>the big hand is on... </li></ul></ul>

378.
Alternative Calendars <ul><li>Handling non-standard calendars

379.
DateTime::Calendar::Julian

380.
DateTime::Calendar::Hebrew

381.
DateTime::Calendar::Mayan

382.
DateTime::Fiction::JRRTolkien::Shire </li></ul>

383.
Calendar Examples <ul><li>use DateTime::Calendar::Mayan; my $dt = DateTime::Calendar::Mayan->now; say $dt->date; # 12.19.16.9.15

384.
use DateTime::Fiction::JRRTolkien::Shire my $dt = DateTime::Fiction::JRRTolkien::Shire->now; say $dt->on_date; # Trewsday 1 Wedmath 7473 </li></ul>

385.
Templates

386.
Templates <ul><li>Many people use templates to produce web pages

387.
Advantages are well known

388.
Standard look and feel (static/dynamic)

389.
Reusable components

390.
Separation of code logic from display logic

391.
Different skill-sets (HTML vs Perl) </li></ul>

392.
Non-Web Templates <ul><li>The same advantages apply to non-web areas

393.
Reports

394.
Business documents

395.
Configuration files

396.
Anywhere you produce output </li></ul>

397.
DIY Templating <ul><li>Must be easy - so many people do it

398.
See perlfaq4

399.
“How can I expand variables in text strings?” </li></ul>

400.
DIY Templating <ul><li>$text = 'this has a $foo in it and a $bar'; %user_defs = ( foo => 23, bar => 19, ); $text =~ s/(+)/$user_defs{$1}/g;

401.
Don't do that </li></ul>

402.
Templating Options <ul><li>Dozens of template modules on CPAN

403.
Text::Template, HTML::Template, Mason, Template Toolkit

404.
Many, many more

405.
Questions to consider </li><ul><li>HTML only?

406.
Template language </li></ul><li>I choose the Template Toolkit </li></ul>

407.
Template Toolkit <ul><li>http://tt2.org/

408.
Very powerful

409.
Both web and non-web

410.
Simple template language

411.
Plugins give access to much of CPAN

412.
Can use Perl code if you want </li><ul><li>But don't do that </li></ul></ul>

413.
Good Book Too!

414.
The Template Equation <ul><li>Data + Template = Output

415.
Data + Alternative Template = Alternative Output

416.
Different views of the same data

417.
Only the template changes </li></ul>

418.
Simple TT Example <ul><li>use Template; use My::Object; my ($id, $format) = @ARGV; $format ||= 'html'; my $obj = My::Object->new($id) or die; my $tt = Template->new; $tt->process(&quot;$format.tt&quot;, { obj => $obj }, &quot;$id.$format&quot;) or die $tt->error; </li></ul>

419.
html.tt <ul><li><html> <head> <title>[% obj.name %]</title> </head> <body> <h1>[% obj.name %]<h1> <p><img src=“[% obj.img %]” /><br /> [% obj.desc %]</p> <ul> [% FOREACH child IN obj.children -%] <li>[% child.name %]</li> [% END %] </body> </html> </li></ul>

420.
text.tt <ul><li>[% obj.name | upper %] Image: [% obj.img %] [% obj.desc %] [% FOREACH child IN obj.children -%] * [% child.name %] [% END %] </li></ul>

421.
Adding New Formats <ul><li>No new code required

422.
Just add new output template

423.
Perl programmer need not be involved </li></ul>

424.
Equation Revisited <ul><li>Data + Template = Output </li><ul><li>Template Toolkit </li></ul><li>Template + Output = Data </li><ul><li>Template::Extract </li></ul><li>Data + Output = Template </li><ul><li>Template::Generate </li></ul></ul>

425.
Databases

426.
Databases <ul><li>A large proportion of applications need to talk to databases

427.
Perl has tools to make this as simple as possible

428.
DBI is the basis for all modern Perl database access

429.
You should be using DBI </li><ul><li>or something based on DBI </li></ul></ul>

430.
How DBI Works <ul><li>Program uses DBI.pm

431.
Create a connection to a particular type of database

432.
DBD module gets loaded

433.
DBD translates from DBI API to database specific calls

434.
DBD translates returned data into Perl data stuctures </li></ul>

435.
Connecting to a DB <ul><li>use DBI; my $dbh = DBI->connect( &quot;dbi:mysql:$some_stuff&quot;, $user, $pass );

436.
“mysql” is the name of the DBD </li><ul><li>DBD::mysql </li></ul><li>In theory you can port a program to another database

437.
Just change the connection line </li></ul>

438.
Selecting Data <ul><li>Prepare the SQL statement

439.
my $sth = $dbh->prepare( 'select name, genre from artist' );

440.
my $sth = $dbh->prepare( &quot;select title, from song where artist = '$id'&quot;);

441.
Check return values (syntax errors) </li></ul>

442.
Selecting Data (cont) <ul><li>Execute the statement

443.
$sth->execute

444.
Still need to check for errors </li></ul>

445.
Selecting Data (cont) <ul><li>Fetch the returned data

446.
while (my @row = $sth->fetchrow_array){ print &quot;@row&quot;; }

447.
Fields are returned in the same order as they are defined in the query </li></ul>

448.
Other Select Functions <ul><li>Other fetch methods are available: </li><ul><li>fetchrow_arrayref

449.
fetchrow_hashref (keys are column names)

450.
fetchall_arrayref

451.
fetch (alias for fetchrow_arrayref) </li></ul><li>Many more added each week </li></ul>

452.
Some Caveats <ul><li>If you're using a fetch method that returns an array </li><ul><li>Never use &quot;select *&quot;

453.
For (hopefully) obvious reasons </li></ul><li>If you're using a fetch method that returns a hash </li><ul><li>Ensure all your columns have (unique) names

454.
For (hopefully) obvious reasons </li></ul></ul>

455.
Insert, Update & Delete <ul><li>Statements that don't return data can be executed the same way

456.
my $sql = &quot;update table1 set col1 = '$val' where id_col = $id&quot;; my $sth = $dbh->prepare($sql); $sth->execute;

457.
But there's a shortcut

458.
$rows = $dbh->do($sql); </li></ul>

459.
Multiple Insertions <ul><li>while (<FILE>) { chomp; my @data = split; my $sql = &quot;insert into tab values ($data[0], $data[1], $data[2]&quot;); $dbh->do($sql); }

460.
Recompiles the SQL every time

461.
Very inefficient </li></ul>

462.
Binding Data <ul><li>Prepare statement once, use many times

463.
my $sql = &quot;insert into tab values (?, ?, ?)&quot;; my $sth = $dbh->prepare($sql); while (<FILE>) { my @data = split; bind_param(1, $data[0]); bind_param(2, $data[1]); bind_param(3, $data[2]); $sth->execute; }

464.
Bonus - binding handles quoting for you </li></ul>

465.
Binding Data (cont) <ul><li>Even easier – extra parameters to execute

466.
my $sql = &quot;insert into tab values (?, ?, ?)&quot;; my $sth = $dbh->prepare($sql); while (<FILE>) { chomp; my @data = split; $sth->execute(@data); } </li></ul>

467.
Unnamed Placeholders <ul><li>Having unnamed placeholders can get confusing

468.
my $sql = 'insert into big_table values( ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)';

469.
Good chance of getting the variables in the wrong order

470.
By the way - there's a basic maintainability error in that SQL </li></ul>

471.
Bind By Name <ul><li>my $sql = 'insert into big_table (id, code, name, addr, email, url, ... ) values (:id, :code, :name, :addr, :email, :url, ... ); my $sth = $sql->prepare($sql); $sth->bind_param(':id', $id); $sth->bind_param(':code', $code); # etc $sth->execute; </li></ul>

472.
Even Easier Binding <ul><li>Store your data in a hash

473.
my %data = (id => 42, code => 'H2G2', ... ); # and later... foreach my $col (keys %data) { $sth->bind_param(&quot;:$col&quot;, $data{$col}; } </li></ul>

474.
Downsides <ul><li>Many DBDs don't support it

475.
Which is a bit of a bugger

476.
Oracle does

477.
So does PostgreSQL (tho' the docs discourage its use)

478.
Check your DBD documentation

479.
Email your friendly neighbourhood DBD author </li></ul>

480.
Some Tips <ul><li>Make your life as easy as possible

481.
Don't hard-code connection data </li><ul><li>Config file, command line options, environment variables </li></ul><li>Send all of your data access through one function

482.
Store SQL queries externally and reference them by name

483.
Use named bind parameters if you can </li></ul>

484.
Sample Code <ul><li>my $dbh; sub run_sql { my ($sql_statement, %args) = @_; my $sql = get_sql($sql_statement); $dbh = get_dbh() unless $dbh; my $sth = $dbh->prepare($sql); foreach my $col (keys %args) { $sth->bind_param(&quot;:$col&quot;, $args{$col}); } return $sth->execute; } </li></ul>

485.
Not Writing SQL <ul><li>Writing SQL is boring

486.
It's often similar </li><ul><li>Select the id and name from this table

487.
Select all the details of this row

488.
Select something about related tables

489.
Update this row with these values

490.
Insert a new record with these values

491.
Delete this record </li></ul><li>Must be a better way </li></ul>

492.
Object Relational Mapping <ul><li>Mapping database relations into objects

493.
Tables (relations) map onto classes

494.
Rows (tuples) map onto objects

495.
Columns (attributes) map onto attributes

496.
Don't write SQL </li></ul>

497.
Replacing SQL <ul><li>Instead of

498.
SELECT * FROM my_table WHERE my_id = 10

499.
and then dealing with the prepare/execute/fetch code </li></ul>

500.
Replacing SQL <ul><li>We can write

501.
use My::Object; # warning! not a real orm my $obj = My::Object->retrieve(10) $obj->name('A New Name'); $obj->save;

502.
Or something similar </li></ul>

503.
ORM on CPAN <ul><li>Very many ORMs on CPAN

504.
Tangram

505.
Alzabo

506.
Class::DBI

507.
DBIx::Class </li><ul><li>The current favourite

508.
Highly recommended </li></ul></ul>

509.
Further Information <ul><li>perldoc DBI

510.
perldoc DBD::* </li><ul><li>DBD::mysql

511.
DBD::Oracle

512.
Etc... </li></ul><li>perldoc DBIx::Class </li></ul>

513.
Further Information

514.
Perl Websites <ul><li>Perl Home Page </li><ul><li>http://www.perl.org </li></ul><li>CPAN </li><ul><li>http://www.cpan.org

515.
http://search.cpan.org </li></ul><li>Perl Mongers (Perl User Groups)‏ </li><ul><li>http://www.pm.org

516.
http://london.pm.org </li></ul></ul>

517.
Perl Websites <ul><li>use.perl – Perl News & Journals </li><ul><li>http://use.perl.org/ </li></ul><li>Perl Monks – Perl Help and Advice </li><ul><li>http://perlmonks.org/ </li></ul><li>Perl Documentation Online </li><ul><li>http://perldoc.perl.org/ </li></ul></ul>

518.
Perl Conferences <ul><li>The Perl Conference (part of the Open Source Convention)‏ </li><ul><li>July 20-24 2009, San Jose, California

519.
http://conferences.oreilly.com/oscon </li></ul><li>Yet Another Perl Conference </li><ul><li>August 3-5 2009, Lisbon, Portugal

520.
http://www.yapceurope.org </li></ul></ul>

521.
Perl Conferences <ul><li>Other YAPCs </li><ul><li>Pittsburgh, Pennsylvania

522.
Brazil

523.
Tokyo </li></ul><li>OSDC </li><ul><li>Israel

524.
Australia </li></ul></ul>

525.
Perl Workshops <ul><li>One-day grassroots conferences

526.
UK, Germany, Israel, Pittsburgh, Nordic, Netherlands, France, Belgium, Russia, Minnesota, Austria

527.
Perl Review Calendar </li><ul><li>www.theperlreview.com/community_calendar </li></ul></ul>

528.
Perl Mailing Lists <ul><li>See http://lists.perl.org for full details </li><ul><li>Perl Mongers (social discussion)‏

529.
CGI

530.
DBI

531.
XML

532.
Beginners

533.
Advocacy

534.
Fun with Perl </li></ul></ul>

535.
Perl Books <ul><li>Books for learning Perl </li><ul><li>Learning Perl (5th ed - June 2008) Schwartz, Phoenix & foy (O'Reilly)‏

536.
Intermediate Perl Schwartz, foy & Phoenix (O'Reilly)‏

537.
Beginning Perl Cozens (Wrox) http://www.perl.org/books/beginning-perl/ </li></ul></ul>

538.
Perl Books <ul><li>Books you should have access to </li><ul><li>Programming Perl (3rd edition) Wall, Christiansen & Orwant (O'Reilly)‏

539.
The Perl Cookbook (2nd edition) Christiansen & Torkington (O'Reilly)‏

540.
Perl Best Practices Conway (O'Reilly)‏

541.
Perl in a Nutshell Siever, Spainhour & Patwardhan (O'Reilly)‏ </li></ul></ul>

542.
Perl Books <ul><li>Books you should probably look at </li><ul><li>Mastering Regular Expressions Friedl (O'Reilly)‏

543.
Data Munging with Perl Cross (Manning)‏

544.
Advanced Perl Programming Cozens (O'Reilly)‏

545.
Perl Medic Scott (Addison Wesley) </li></ul></ul>

546.
Perl Books <ul><li>Specialised Perl books </li><ul><li>Object Oriented Perl Conway (Manning)‏

547.
Programming the Perl DBI Descartes & Bunce (O'Reilly)‏

548.
Writing CGI Applications with Perl Meltzer & Michelski (Addison Wesley)‏

549.
Practical mod_perl Bekman & Cholet (O'Reilly)‏

550.
Perl Template Toolkit Chamberlain, Cross & Wardley </li></ul></ul>

551.
Perl Magazines <ul><li>The Perl Review </li><ul><li>http://www.theperlreview.com </li></ul></ul>

552.
That's All Folks <ul><li>Any Questions? </li></ul>