Introduction to
Perl Best Practices
José Castro <cog@cpan.org>
Tokyo, September 2009

Who am I?
• Perl Hacker from Portugal
• COG@CPAN
• YAPC::EU::20{04,05,06,07,08,09},
YAPC::NA::20{05,06,07,08},
YAPC::Asia 20{08,09}, LPW 20{04,05},
PPW 2008, OSDC::AU 2006
• Technology Evangelist @ SAPO
SAPO/Portugal
Telecom

What is SAPO?

What is SAPO?

What is SAPO?
• Older than Google,
kind of like Yahoo!

What is SAPO?
• Older than Google,
kind of like Yahoo!
• 100+ techs

What is SAPO?
• Older than Google,
kind of like Yahoo!
• 100+ techs
• 100+ non-techs

What is SAPO?
• Older than Google,
kind of like Yahoo!
• 100+ techs
• 100+ non-techs
• Mail, Blogs, Photos,Videos, Links, Cars, Real
Estate, Jobs, Maps, Encyclopedia online,
Search, Messaging, Social Network, etc., etc.,
etc.

What do I do at SAPO?

What do I do at SAPO?
• Evangelism (motivation, productivity, quality)

What do I do at SAPO?
• Evangelism (motivation, productivity, quality)
• Organize the training program

What do I do at SAPO?
• Evangelism (motivation, productivity, quality)
• Organize the training program
• Recruitment (lots of interviews every week)

What do I do at SAPO?
• Evangelism (motivation, productivity, quality)
• Organize the training program
• Recruitment (lots of interviews every week)
• Organize events

What do I do at SAPO?
• Evangelism (motivation, productivity, quality)
• Organize the training program
• Recruitment (lots of interviews every week)
• Organize events
• Etc.

Introduction to
Perl Best Practices
José Castro <cog@cpan.org>
Tokyo, September 2009

“What?”
• a set of suggestions/guidelines to improve
your code’s readability and reliability

Disclaimer
• what works for a particular situation may
not be adequate for another
• YMMV

“Why?”
• tomorrow, you may need to fix a glitch in
your code
• next week, you may need to confirm
something
• 6 months from now, you may need to
develop a new feature

“How?”
• using standards
• defining your best practices and following
them

Code Sample #1

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

Block separation
• A program is a list of instructions
• You’re writing it as a letter
• Separate your paragraphs, for clarity

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

Separate instructions
• Each instruction should have its own line

use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi ');
my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

Indentation
• 2 spaces?
• 4 spaces?
• 6, 8?
• Tabs?

use strict;
my @list=('Emacs', 'Vi ');
my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi ');
my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

Spaces around
operators
• Don’t clutter things up
• Spaces around operators help you find
them more easily

use strict;
my @list=('Emacs', 'Vi ');
my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list=('Emacs', 'Vi ');
my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @list = ('Emacs', 'Vi ');
my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i = int ($rand + rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

Naming variables
• Don’t name them “var”, “list”, “hash” or
anything else that does not have a meaning
• Make sure the name helps you identify
what it is

use strict;
my @list = ('Emacs', 'Vi ');
my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i = int ($rand + rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

use strict;
my @editors = ('Emacs', 'Vi ');
my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i = int ($rand + rand());
print " $editors[$i] users are from Venus" . ",
"$editors[1-$i] users are from Mars" .
"n";
}

Vertical indentation
• Vertical indentation helps your eyes find
things more easily

use strict;
my @editors = ('Emacs', 'Vi ');
my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i = int ($rand + rand());
print " $editors[$i] users are from Venus" . ",
"$editors[1-$i] users are from Mars" .
"n";
}

use strict;
my @editors = ('Emacs', 'Vi ');
my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i = int ($rand + rand());
print " $editors[$i] users are from Venus" . ",
"$editors[1-$i] users are from Mars" .
"n";
}

Code Sample #2

my @list = (2,3,5,7,11,13,17,19,23,29,31,37,41,43,47
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,144,233,377,
for my $number (@list) {
if (grep{$number==$_}@list2) {print "$number is
}

my @list = (2,3,5,7,11,13,17,19,23,29,31,37,41,43,47
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,144,233,377,
for my $number (@list) {
if (grep{$number==$_}@list2) {print "$number is
}

my @list = (2,3,5,7,11,13,17,19,23,29,31,37,41,43,47
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,144,233,377,
for my $number (@list) {
if (grep{$number==$_}@list2) {print "$number is
}

my @list = (2,3,5,7,11,13,17,19,23,29,31,37,41,43,47
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,144,233,377,
for my $number (@list) {
if (grep{$number==$_}@list2) {print "$number is
}

my @list = (2,3,5,7,11,13,17,19,23,29,31,37,41,43,47
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,144,233,377,
for my $number (@list) {
if (grep{$number==$_}@list2) {print "$number is
}

2 is both a prime number and a fibonacci number
3 is both a prime number and a fibonacci number
5 is both a prime number and a fibonacci number
13 is both a prime number and a fibonacci number
89 is both a prime number and a fibonacci number

Strict and warnings
• both strict and warnings will help you avoid
lots of pesky mistakes

my @list = (2,3,5,7,11,13,17,19,23,29,31,37,41,43,47
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,144,233,377,
for my $number (@list) {
if (grep{$number==$_}@list2) {print "$number is
}

use strict;
use warnings;
my @list = (2,3,5,7,11,13,17,19,23,29,31,37,41,43,47
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,144,233,377,
for my $number (@list) {
if (grep{$number==$_}@list2) {print "$number is
}

Avoid lines over 80 charac
• code is easier to read if it fits on the screen
• even if using line wrapping, having to figure
out if two lines are different instructions or
the same one is harder than not having to
do it

use strict;
use warnings;
my @list = (2,3,5,7,11,13,17,19,23,29,31,37,41,43,47
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,144,233,377,
for my $number (@list) {
if (grep{$number==$_}@list2) {print "$number is
}

use strict;
use warnings;
my @list = (2,3,5,7,11,13,17,19,23,29,31,
37,41,43,47,53,59,61,67,71,73,79,83,89,97,101) ;
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,
144,233,377,610,987,1597,2584,4181,6765) ;
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number and a
}

use strict;
use warnings;
my @list = (2,3,5,7,11,13,17,19,23,29,31,
37,41,43,47,53,59,61,67,71,73,79,83,89,97,101) ;
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,
144,233,377,610,987,1597,2584,4181,6765) ;
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number " . " a
}

use strict;
use warnings;
my @list = (2,3,5,7,11,13,17,19,23,29,31,
37,41,43,47,53,59,61,67,71,73,79,83,89,97,101) ;
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,
144,233,377,610,987,1597,2584,4181,6765) ;
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

When breaking lines,
align vertically
• a broken line is a visual accident waiting to
happen

use strict;
use warnings;
my @list = (2,3,5,7,11,13,17,19,23,29,31,
37,41,43,47,53,59,61,67,71,73,79,83,89,97,101) ;
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,
144,233,377,610,987,1597,2584,4181,6765) ;
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

use strict;
use warnings;
my @list = (2,3,5,7,11,13,17,19,23,29,31,
37,41,43,47,53,59,61,67,71,73,79,83,89,9
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,
144,233,377,610,987,1597,2584,4181,6765
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

Add spaces after a
comma
• spaces after a comma help you visually
separate items

use strict;
use warnings;
my @list = (2,3,5,7,11,13,17,19,23,29,31,
37,41,43,47,53,59,61,67,71,73,79,83,89,9
my @list2 = (1,1,2,3,5,8,13,21,34,55,89,
144,233,377,610,987,1597,2584,4181,6765
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

use strict;
use warnings;
my @list = (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31,
37, 41, 43, 47, 53, 59, 61, 67, 71, 73,
my @list2 = (1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89,
144, 233, 377, 610, 987, 1597, 2584, 41
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

Organize long lists
as tables
• the brain identifies patterns such as tables
much more easily

use strict;
use warnings;
my @list = (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31,
37, 41, 43, 47, 53, 59, 61, 67, 71, 73,
my @list2 = (1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89,
144, 233, 377, 610, 987, 1597, 2584, 41
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

use strict;
use warnings;
my @list = ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29,
37, 41, 43, 47, 53, 59, 61, 67, 71, 73,
my @list2 = (1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89,
144, 233, 377, 610, 987, 1597, 2584, 41
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

use strict;
use warnings;
my @list = ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29,
37, 41, 43, 47, 53, 59, 61, 67, 71, 73,
my @list2 = ( 1, 1, 2, 3, 5, 8, 13, 2
144, 233, 377, 610, 987, 1597, 2584, 41
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

Again, name variables
appropriately
• the brain identifies patterns such as tables
much more easily

use strict;
use warnings;
my @list = ( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29,
37, 41, 43, 47, 53, 59, 61, 67, 71, 73,
my @list2 = ( 1, 1, 2, 3, 5, 8, 13, 2
144, 233, 377, 610, 987, 1597, 2584, 41
for my $number (@list) {
if (grep{$number==$_}@list2) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

use strict;
use warnings;
my @prime_numbers = ( 2, 3, 5, 7, 11, 13, 17, 19,
37, 41, 43, 47, 53, 59, 61, 67,
my @fibonnaci = ( 1, 1, 2, 3, 5, 8,
144, 233, 377, 610, 987, 1597,
for my $number (@prime_numbers) {
if (grep{$number==$_}@fibonnaci) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

Spaces for clarity
• around operators
• around blocks
• around anything else that may cause
confusion

use strict;
use warnings;
my @prime_numbers = ( 2, 3, 5, 7, 11, 13, 17, 19,
37, 41, 43, 47, 53, 59, 61, 67,
my @fibonnaci = ( 1, 1, 2, 3, 5, 8,
144, 233, 377, 610, 987, 1597,
for my $number (@prime_numbers) {
if (grep{$number==$_}@fibonnaci) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

use strict;
use warnings;
my @prime_numbers = ( 2, 3, 5, 7, 11, 13, 17, 19,
37, 41, 43, 47, 53, 59, 61, 67,
my @fibonnaci = ( 1, 1, 2, 3, 5, 8,
144, 233, 377, 610, 987, 1597,
for my $number (@prime_numbers) {
if ( grep { $number == $_ } @fibonnaci ) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

Block closing
• the closing curly brace should be in a line
by itself
• this helps better identify where the block
ends

use strict;
use warnings;
my @prime_numbers = ( 2, 3, 5, 7, 11, 13, 17, 19,
37, 41, 43, 47, 53, 59, 61, 67,
my @fibonnaci = ( 1, 1, 2, 3, 5, 8,
144, 233, 377, 610, 987, 1597,
for my $number (@prime_numbers) {
if ( grep { $number == $_ } @fibonnaci ) {
print "$number is both a prime number " .
" and a fibonacci numbern"}
}

use strict;
use warnings;
my @prime_numbers = ( 2, 3, 5, 7, 11, 13, 17, 19,
37, 41, 43, 47, 53, 59, 61, 67,
my @fibonnaci = ( 1, 1, 2, 3, 5, 8,
144, 233, 377, 610, 987, 1597,
for my $number (@prime_numbers) {
if ( grep { $number == $_ } @fibonnaci ) {
print "$number is both a prime number " .
" and a fibonacci numbern"
}
}

Always end a statement
with a semicolon
• even if it’s the last statement in the block
• even if the closing curly brace is on the
same line
• this will allow you to add another
statement without having to check the line
above

use strict;
use warnings;
my @prime_numbers = ( 2, 3, 5, 7, 11, 13, 17, 19,
37, 41, 43, 47, 53, 59, 61, 67,
my @fibonnaci = ( 1, 1, 2, 3, 5, 8,
144, 233, 377, 610, 987, 1597,
for my $number (@prime_numbers) {
if ( grep { $number == $_ } @fibonnaci ) {
print "$number is both a prime number " .
" and a fibonacci numbern"
}
}

use strict;
use warnings;
my @prime_numbers = ( 2, 3, 5, 7, 11, 13, 17, 19,
37, 41, 43, 47, 53, 59, 61, 67,
my @fibonnaci = ( 1, 1, 2, 3, 5, 8,
144, 233, 377, 610, 987, 1597,
for my $number (@prime_numbers) {
if ( grep { $number == $_ } @fibonnaci ) {
print "$number is both a prime number " .
" and a fibonacci numbern";
}
}

Inside a loop, use empty
lines around the body
• this is also going to help you identify the
beginning and the end of the loop

use strict;
use warnings;
my @prime_numbers = ( 2, 3, 5, 7, 11, 13, 17, 19,
37, 41, 43, 47, 53, 59, 61, 67,
my @fibonnaci = ( 1, 1, 2, 3, 5, 8,
144, 233, 377, 610, 987, 1597,
for my $number (@prime_numbers) {
if ( grep { $number == $_ } @fibonnaci ) {
print "$number is both a prime number " .
" and a fibonacci numbern";
}
}

use strict;
use warnings;
my @prime_numbers = ( 2, 3, 5, 7, 11, 13, 17, 19,
37, 41, 43, 47, 53, 59, 61, 67,
my @fibonnaci = ( 1, 1, 2, 3, 5, 8,
144, 233, 377, 610, 987, 1597,
for my $number (@prime_numbers) {
if ( grep { $number == $_ } @fibonnaci ) {
print "$number is both a prime number " .
" and a fibonacci numbern";
}
}

Code Sample #3

for my $number (@prime_numbers) {
if ( grep { $number == $_ } @fibonnaci ) {
print "$number is both a prime number " .
" and a fibonacci numbern";
}
}

if ( grep { $number == $_ } @fibonnaci ) {

Using CPAN
• Many modules on CPAN already implement
what we need in a far better way than we
could possibly do in a couple of minutes

grep { 2 == $_ }
( 1, 1, 2, 3, 5, 8, 13,
21, 34, 55, 89, 144, 233, 377,
610, 987, 1597, 2584, 4181, 6765, 10946)
if ( grep { $number == $_ } @fibonnaci ) {

grep { 2 == $_ }
( 1, 1, 2, 3, 5, 8, 13,
21, 34, 55, 89, 144, 233, 377,
610, 987, 1597, 2584, 4181, 6765, 10946)
if ( grep { $number == $_ } @fibonnaci ) {

grep { 2 == $_ }
( 1, 1, 2, 3, 5, 8, 13,
21, 34, 55, 89, 144, 233, 377,
610, 987, 1597, 2584, 4181, 6765, 10946)
if ( grep { $number == $_ } @fibonnaci ) {

grep { 2 == $_ }
( 1, 1, 2, 3, 5, 8, 13,
21, 34, 55, 89, 144, 233, 377,
610, 987, 1597, 2584, 4181, 6765, 10946)
if ( grep { $number == $_ } @fibonnaci ) {

grep { 2 == $_ }
( 1, 1, 2, 3, 5, 8, 13,
21, 34, 55, 89, 144, 233, 377,
610, 987, 1597, 2584, 4181, 6765, 10946)
if ( grep { $number == $_ } @fibonnaci ) {

grep { 2 == $_ }
( 1, 1, 2, 3, 5, 8, 13,
21, 34, 55, 89, 144, 233, 377,
610, 987, 1597, 2584, 4181, 6765, 10946)
if ( grep { $number == $_ } @fibonnaci ) {

grep { 2 == $_ }
( 1, 1, 2, 3, 5, 8, 13,
21, 34, 55, 89, 144, 233, 377,
610, 987, 1597, 2584, 4181, 6765, 10946)
n iterations, always
if ( grep { $number == $_ } @fibonnaci ) {

if ( grep { $number == $_ } @fibonnaci ) {

use List::MoreUtils qw(any);
if ( grep { $number == $_ } @fibonnaci ) {

use List::MoreUtils qw(any);
if ( any { $number == $_ } @fibonnaci ) {

Structure
• separate your code in subroutines
• subroutines should have meaningful names

use List::MoreUtils qw(any);
if ( any { $number == $_ } @fibonnaci ) {

use List::MoreUtils qw(any);
if ( is_fibonnaci($number) ) {
sub is_fibonnaci {
my $number = shift;
return any { $number == $_ } @fibonnaci
}

for my $number (@prime_numbers) {
if ( grep { $number == $_ } @fibonnaci ) {
print "$number is both a prime number " .
" and a fibonacci numbern";
}
}

for my $number (@prime_numbers) {
if ( is_fibonnaci($number) ) {
print "$number is both a prime number " .
" and a fibonacci numbern";
}
}

for my $number (@prime_numbers) {
if ( is_fibonnaci($number) ) {
print "$number is both a prime number " .
" and a fibonacci numbern";
}
}
sub is_fibonnaci {
my $number = shift;
return any { $number == $_ } @fibonnaci;

for my $number (@prime_numbers) {
if ( is_fibonnaci($number) ) {
print "$number is both a prime number " .
" and a fibonacci numbern";
}
}

for (@prime_numbers) {
if ( is_fibonnaci($_) ) {
print "$_ is both a prime number " .
" and a fibonacci numbern";
}
}

Code Sample #4

for ( 1 .. 1000000000 ) {
my $flag = 1;
$flag = 0 if is_prime( $_ );
$flag = 0 if is_fibonnaci( $_ );
if ( $flag ) {
print "$_ seems interestingn";
}
}

for ( 1 .. 1000000000 ) {
my $flag = 1;
$flag = 0 if is_prime( $_ );
$flag = 0 if is_fibonnaci( $_ );
if ( $flag ) {
print "$_ seems interestingn";
}
}

for ( 1 .. 1000000000 ) {
my $flag = 1;
$flag = 0 if is_prime( $_ );
$flag = 0 if is_fibonnaci( $_ );
if ( $flag ) {
print "$_ seems interestingn";
}
}

for ( 1 .. 1000000000 ) {
my $flag = 1;
$flag = 0 if is_prime( $_ );
$flag = 0 if is_fibonnaci( $_ );
if ( $flag ) {
print "$_ seems interestingn";
}
}

for ( 1 .. 1000000000 ) {
my $flag = 1;
$flag = 0 if is_prime( $_ );
$flag = 0 if is_fibonnaci( $_ );
if ( $flag ) {
print "$_ seems interestingn";
}
}

for ( 1 .. 1000000000 ) {
my $flag = 1;
$flag = 0 if is_prime( $_ );
$flag = 0 if is_fibonnaci( $_ );
if ( $flag ) {
print "$_ seems interestingn";
}
}

Underscores
for large numbers
• Large numbers are hard to read
• Underscores every three digits can help

for ( 1 .. 1000000000 ) {
my $flag = 1;
$flag = 0 if is_prime( $_ );
$flag = 0 if is_fibonnaci( $_ );
if ( $flag ) {
print "$_ seems interestingn";
}
}

for ( 1 .. 1_000_000_000 ) {
my $flag = 1;
$flag = 0 if is_prime( $_ );
$flag = 0 if is_fibonnaci( $_ );
if ( $flag ) {
print "$_ seems interestingn";
}
}

Booleans
• flags shouldn’t be named “flag”
• they should have intuitive names

for ( 1 .. 1_000_000_000 ) {
my $flag = 1;
$flag = 0 if is_prime( $_ );
$flag = 0 if is_fibonnaci( $_ );
if ( $flag ) {
print "$_ seems interestingn";
}
}

for ( 1 .. 1_000_000_000 ) {
my $is_interesting = 1;
$is_interesting = 0 if is_prime( $_ );
$is_interesting = 0 if is_fibonnaci( $_ );
if ( $is_interesting ) {
print "$_ seems interestingn";
}
}

Tools and helpers

Perl Best Practices
@M" I.'(9)*'$.&8$'.(,8(/=+$8C'(,-'($'%*%?/5/,4(8<(58)>()9=?'$."
DO" X%4(89,(=95,/5/)'(.,$/)>.(8C'$(=95,/+5'(5/)'."
Documentation
D!" I.'(%(-'$'*8&(;-')(%(=95,/5/)'(.,$/)>('G&''*.(,;8(5/)'." LF" A/.,/)>9/.-(9.'$(*8&9='),%,/8)(<$8=(,'&-)/&%5(*8&9='),%,/8)"
D6" I.'(%(E,-'$'*8&B(;-')(%(-'$'*8&(;895*(&8=+$8=/.'(489$(/)*'),%N LH" S$'%,'(.,%)*%$*(K_A(,'=+5%,'.(<8$(=8*95'.(%)*(%++5/&%,/8)."
Reference Guide D@"
,/8)"
W%:'('C'$4(-'$'*8&(,'$=/)%,8$(%(./)>5'(9++'$&%.'(/*'),/</'$(;/,-(%(
LJ"
LL"
VG,')*(%)*(&9.,8=/0'(489$(.,%)*%$*(K_A(,'=+5%,'."
K9,(9.'$(*8&9='),%,/8)(/)(.89$&'(</5'."
.,%)*%$*(+$'</G" LM" 1''+(%55(9.'$(*8&9='),%,/8)(/)(%(./)>5'(+5%&'(;/,-/)(489$(.89$&'(
DD" Y-')(/),$8*9&/)>(%(-'$'*8&Q(Z98,'(,-'(,'$=/)%,8$" </5'"
Code Layout DF" A8)B,(9.'(?%$';8$*." MO" K5%&'(K_A(%.(&58.'(%.(+8../?5'(,8(,-'(')*(8<(,-'(</5'"
DH" 3'.'$C'(#$(<8$(+%/$." M!" 79?*/C/*'(489$(,'&-)/&%5(*8&9='),%,/8)(%++$8+$/%,'54"
!" #$%&'(%)*(+%$'),-'./0'(/)(123(.,45'"
DJ" A8)B,(9.'(&8==%.(,8(.'Z9')&'(.,%,'='),." M6" I.'(?58&:(,'=+5%,'.(<8$(=%^8$(&8=='),."
6" 7'+%$%,'(489$(&8),$85(:'4;8$*.(<$8=(,-'(<8558;/)>(8+')/)>(
DL" A8)B,(=/G(-/>-N(%)*(58;N+$'&'*')&'(?885'%)." M@" I.'(<955N5/)'(&8=='),.(,8('G+5%/)(,-'(%5>8$/,-="
?$%&:',"
DM" K%$'),-'./0'('C'$4($%;(5/.," MD" I.'(')*N8<N5/)'(&8=='),.(,8(+8/),(89,(.9?,5',/'.(%)*(8**/,/'."
@" A8)B,(.'+%$%,'(.9?$89,/)'(8$(C%$/%?5'()%='.(<$8=(,-'(<8558;/)>(
FO" I.'(,%?5'N588:9+(,8(,'.,(<8$(='=?'$.-/+(/)(5/.,.(8<(.,$/)>.[(9.'(+),%&' MF" S8=='),(%)4,-/)>(,-%,(-%.(+9005'*(8$(,$/&:'*(489"
8+')/)>(?$%&:',"
<8$(='=?'$.-/+(8<(5/.,.(8<(%)4,-/)>('5.'" MH" S8)./*'$(;-',-'$(/,B.(?',,'$(,8($';$/,'(,-%)(,8(&8=='),"
D" A8)B,(9.'(9))'&'..%$4(+%$'),-'.'.(<8$(?9/5,/).(%)*(E-8)8$%$4B(
MJ" I.'(E/)C/./?5'B(K_A(.'&,/8).(<8$(58)>'$(,'&-)/&%5(*/.&9../8)."
?9/5,/)."
F" 7'+%$%,'(&8=+5'G(:'4.(8$(/)*/&'.(<$8=(,-'/$(.9$$89)*/)>(?$%&:',." Variables ML" S-'&:(,-'(.+'55/)>Q(.4),%GQ(%)*(.%)/,4(8<(489$(*8&9='),%,/8)"
H" I.'(;-/,'.+%&'(,8(-'5+(?/)%$4(8+'$%,8$.(.,%)*(89,(<$8=(,-'/$( F!" TC8/*(9./)>()8)N5'G/&%5(C%$/%?5'."
8+'$%)*." F6" A8)B,(9.'(+%&:%>'(C%$/%?5'.(/)(489$(8;)(*'C'58+='),"
Built-in Functions
J" K5%&'(%(.'=/&858)(%<,'$('C'$4(.,%,'=')," F@" P<(489B$'(<8$&'*(,8(=8*/<4(%(+%&:%>'(C%$/%?5'Q("('+"/0'(/," MM" A8)B,($'&8=+9,'(.8$,(:'4.(/)./*'(%(#(%*"
L" K5%&'(%(&8==%(%<,'$('C'$4(C%59'(/)(%(=95,/5/)'(5/.," !OO" I.'(%!8!%#!(,8($'C'$.'(%(5/.,"
FD" P)/,/%5/0'(%)4(C%$/%?5'(489("('+"/0'"
M" I.'(JLN&859=)(5/)'."
FF" -#!./)0"1#2(<8$(,-'(5'..(<%=/5/%$(+9)&,9%,/8)(C%$/%?5'." !O!" I.'(.&%5%$(%!8!%#!(,8($'C'$.'(%(.&%5%$"
!O" I.'(<89$N&859=)(/)*'),%,/8)(5'C'5."
FH" P<(489B$'(<8$&'*(,8(=8*/<4(%(+9)&,9%,/8)(C%$/%?5'Q("('+"/0'(/," !O6" I.'(-)5+'9 (,8('G,$%&,(</G'*N;/*,-(</'5*."
!!" P)*'),(;/,-(.+%&'.Q()8,(,%?."
!6" R'C'$(+5%&'(,;8(.,%,'='),.(8)(,-'(.%='(5/)'" FJ" A8)B,(9.'(,-'($'>'G(=%,&-(C%$/%?5'." !O@" I.'(#5"1*(,8('G,$%&,(./=+5'(C%$/%?5'N;/*,-(</'5*."
!@" S8*'(/)(+%$%>$%+-." FL" #';%$'(8<(%)4(=8*/</&%,/8)(C/%(()" !OD" I.'(*+,-../01)20(,8('G,$%&,(&8=+5'G(C%$/%?5'N;/*,-(</'5*."
!D" A8)B,(&9**5'(%)(!"#!"
FM" I.'()'>%,/C'(/)*/&'.(;-')(&89),/)>(<$8=(,-'(')*(8<(%)(%$$%4" !OF" TC8/*(.,$/)>(!8+""
HO" %:'(%*C%),%>'(8<(-%.-(%)*(%$$%4(.5/&/)>" !OH" S8)./*'$(?9/5*/)>(489$(.8$,/)>($89,/)'.(;/,-(034-..567+4"
!F" T5/>)(&8$$'.+8)*/)>(/,'=.(C'$,/&%554"
H!" I.'(%(,%?95%$(5%489,(<8$(.5/&'." !OJ" I.'(DN%$>(#-:#*%(/).,'%*(8<(5C%59'(#-:#*%"
!H" #$'%:(58)>('G+$'../8).(?'<8$'(%)(8+'$%,8$"
H6" U%&,8$(5%$>'(:'4(8$(/)*'G(5/.,.(89,(8<(,-'/$(.5/&'." !OL" W%:'(%++$8+$/%,'(9.'(8<(5C%59'(C%59'."
!J" U%&,8$(89,(58)>('G+$'../8).(/)(,-'(=/**5'(8<(.,%,'='),."
!L" T5;%4.(?$'%:(%(58)>('G+$'../8)(%,(,-'(8+'$%,8$(8<(,-'(58;'.,(+8../N !OM" I.'(0"(:Q()8,(8]$"
?5'(+$'&'*')&'" Control Structures !!O" TC8/*(%($%;(#!"!'*(<8$()8)N/),'>'$(.5''+."
!M" #$'%:(58)>(%../>)='),.(?'<8$'(,-'(%../>)='),(8+'$%,8$" !!!" T5;%4.(9.'(%(?58&:(;/,-(%(4+5(%)*(0%!5"
H@" I.'(?58&:(1&Q()8,(+8.,</G(1&" !!6" I.'(,-'(E)8)N?9/5,/)(?9/5,/).B"
6O" U8$=%,(&%.&%*'*(,'$)%$4(8+'$%,8$.(/)(&859=)." HD" 3'.'$C'(+8.,</G(1&(<8$(<58;N8<N&8),$85(.,%,'='),."
6!" K%$'),-'./0'(58)>(5/.,."
HF" A8)B,(9.'(+8.,</G(-)"!##Q(&(%Q(321"!Q(8$(-)*1""
66" V)<8$&'(489$(&-8.')(5%489,(.,45'(='&-%)/&%554"
HH" A8)B,(9.'(-)"!##(8$(-)*1"(%,(%55" Subroutines
HJ" TC8/*(SN.,45'(&(%(.,%,'='),." !!@" S%55(.9?$89,/)'.(;/,-(+%$'),-'.'.(?9,(;/,-89,(%(5'%*/)>(9"
Naming Conventions HL" TC8/*(.9?.&$/+,/)>(%$$%4.(8$(-%.-'.(;/,-/)(588+." !!D" A8)B,(>/C'(.9?$89,/)'.(,-'(.%='()%='.(%.(?9/5,N/)(<9)&,/8)."
6@" I.'(>$%==%,/&%5(,'=+5%,'.(;-')(<8$=/)>(/*'),/</'$." HM" R'C'$(.9?.&$/+,(=8$'(,-%)(8)&'(/)(%(588+" !!F" T5;%4.(9)+%&:(:)(</$.,"
6D" R%='(?885'%).(%<,'$(,-'/$(%..8&/%,'*(,'.," JO" I.'()%='*(5'G/&%5.(%.('G+5/&/,(&(%(588+(/,'$%,8$." !!H" I.'(%(-%.-(8<()%='*(%$>9='),.(<8$(%)4(.9?$89,/)'(,-%,(-%.(=8$'(
6F" W%$:(C%$/%?5'.(,-%,(.,8$'($'<'$')&'.(;/,-(%($%!&(.9<</G" J!" T5;%4.(*'&5%$'(%(&(%(588+(/,'$%,8$(C%$/%?5'(;/,-(4," ,-%)(,-$''(+%$%=','$."
6H" R%='(%$$%4.(/)(,-'(+59$%5(%)*(-%.-'.(/)(,-'(./)>95%$" J6" I.'(4+5(/).,'%*(8<(&(%(;-')(>')'$%,/)>()';(5/.,.(<$8=(85*" !!J" I.'(6!&1)!6)'..(8$(!71#*')&'(,8(,'.,(<8$(=/../)>(%$>9='),."
6J" I.'(9)*'$.&8$'.(,8(.'+%$%,'(;8$*.(/)(=95,/;8$*(/*'),/</'$." J@" I.'(0%!5(%)*(&1%#*(/).,'%*(8<(&(%(;-')(.'%$&-/)>(<8$(C%59'.(/)(%(5/.," !!L" 3'.85C'(%)4(*'<%95,(%$>9='),(C%59'.(%.(.88)(%.(:)(/.(9)+%&:'*"
6L" A/.,/)>9/.-(*/<<'$'),(+$8>$%=(&8=+8)'),.(?4(&%.'" JD" I.'(&(%(/).,'%*(8<(4+5(;-')(,$%).<8$=/)>(%(5/.,(/)(+5%&'" !!M" T5;%4.($',9$)(.&%5%$(/)(.&%5%$($',9$)."
6M" T??$(/*'),.(?4(+$'<G" JF" I.'(%(.9?$89,/)'(&%55(,8(<%&,8$(89,(&8=+5'G(5/.,(,$%).<8$=%,/8)." !6O" W%:'(5/.,N$',9$)/)>(.9?$89,/)'.($',9$)(,-'(E8?C/89.B(C%59'(/)(.&%5%$(
@O" T??$'C/%,'(8)54(;-')(,-'(='%)/)>($'=%/).(9)%=?/>989." JH" R'C'$(=8*/<4(()(/)(%(5/.,(<9)&,/8)" &8),'G,"
@!" TC8/*(9./)>(/)-'$'),54(%=?/>989.(;8$*.(/)()%='." JJ" TC8/*(&%.&%*/)>(%)(1&" !6!" Y-')(,-'$'(/.()8(E8?C/89.B(.&%5%$(&8),'G,($',9$)(C%59'Q(&8)./*'$(
@6" K$'</G(E<8$(/),'$)%5(9.'(8)54B(.9?$89,/)'.(;/,-(%)(9)*'$.&8$'" JL" I.'(,%?5'(588:N9+(/)(+$'<'$')&'(,8(&%.&%*'*('Z9%5/,4(,'.,." /3;-+,-<6=..>+-<4;(/).,'%*"
JM" Y-')(+$8*9&/)>(%(C%59'Q(9.'(,%?95%$(,'$)%$/'." !66" A8)B,(9.'(.9?$89,/)'(+$8,8,4+'."
T5;%4.($',9$)(C/%(%)('G+5/&/,(%!*-%)"
Values and Expressions LO" A8)B,(9.'(6(]321"!(588+." !6@"
!6D" I.'(%(?%$'(%!*-%)(,8($',9$)(<%/59$'"
L!" 3'^'&,(%.(=%)4(/,'$%,/8).(%.(+8../?5'Q(%.('%$54(%.(+8../?5'"
@@" I.'(/),'$+85%,/)>(.,$/)>(*'5/=/,'$.(8)54(<8$(.,$/)>.(,-%,(%&,9%554(/),'$N L6" A8)B,(&8),8$,(588+(.,$9&,9$'.(^9.,(,8(&8).85/*%,'(&8),$85"
+85%,'"
@D" A8)B,(9.'(!!(8$(""(<8$(%)('=+,4(.,$/)>"
L@" I.'(&(%(%)*(%!6((/).,'%*(8<(%)(/$$'>95%$54(&89),'*(321"!" I/O
LD" X%?'5('C'$4(588+(,-%,(/.('G/,'*('G+5/&/,54Q(%)*(9.'(,-'(5%?'5(;/,-(
@F" A8)B,(;$/,'(8)'N&-%$%&,'$(.,$/)>.(/)(C/.9%554(%=?/>989.(;%4." !6F" A8)B,(9.'(?%$';8$*(</5'-%)*5'."
'C'$4()!7*Q("+#*Q(8$(%!6(" !6H" I.'(/)*/$'&,(</5'-%)*5'."
@H" I.'()%='*(&-%$%&,'$('.&%+'.(/).,'%*(8<()9='$/&('.&%+'."
@J" I.'()%='*(&8).,%),.Q(?9,(*8)B,(9.'('()#*+)*" !6J" P<(489(-%C'(,8(9.'(%(+%&:%>'(</5'-%)*5'Q("('+"/0'(/,(</$.,"
@L" A8)B,(+%*(*'&/=%5()9=?'$.(;/,-(5'%*/)>(0'$8."

Perl Best Practices
@M" I.'(9)*'$.&8$'.(,8(/=+$8C'(,-'($'%*%?/5/,4(8<(58)>()9=?'$."
DO" X%4(89,(=95,/5/)'(.,$/)>.(8C'$(=95,/+5'(5/)'."
Documentation
D!" I.'(%(-'$'*8&(;-')(%(=95,/5/)'(.,$/)>('G&''*.(,;8(5/)'." LF" A/.,/)>9/.-(9.'$(*8&9='),%,/8)(<$8=(,'&-)/&%5(*8&9='),%,/8)"
D6" I.'(%(E,-'$'*8&B(;-')(%(-'$'*8&(;895*(&8=+$8=/.'(489$(/)*'),%N LH" S$'%,'(.,%)*%$*(K_A(,'=+5%,'.(<8$(=8*95'.(%)*(%++5/&%,/8)."
Reference Guide D@"
,/8)"
W%:'('C'$4(-'$'*8&(,'$=/)%,8$(%(./)>5'(9++'$&%.'(/*'),/</'$(;/,-(%(
LJ"
LL"
VG,')*(%)*(&9.,8=/0'(489$(.,%)*%$*(K_A(,'=+5%,'."
K9,(9.'$(*8&9='),%,/8)(/)(.89$&'(</5'."
.,%)*%$*(+$'</G" LM" 1''+(%55(9.'$(*8&9='),%,/8)(/)(%(./)>5'(+5%&'(;/,-/)(489$(.89$&'(
DD" Y-')(/),$8*9&/)>(%(-'$'*8&Q(Z98,'(,-'(,'$=/)%,8$" </5'"
Code Layout DF" A8)B,(9.'(?%$';8$*." MO" K5%&'(K_A(%.(&58.'(%.(+8../?5'(,8(,-'(')*(8<(,-'(</5'"
DH" 3'.'$C'(#$(<8$(+%/$." M!" 79?*/C/*'(489$(,'&-)/&%5(*8&9='),%,/8)(%++$8+$/%,'54"
!" #$%&'(%)*(+%$'),-'./0'(/)(123(.,45'"
DJ" A8)B,(9.'(&8==%.(,8(.'Z9')&'(.,%,'='),." M6" I.'(?58&:(,'=+5%,'.(<8$(=%^8$(&8=='),."
6" 7'+%$%,'(489$(&8),$85(:'4;8$*.(<$8=(,-'(<8558;/)>(8+')/)>(
DL" A8)B,(=/G(-/>-N(%)*(58;N+$'&'*')&'(?885'%)." M@" I.'(<955N5/)'(&8=='),.(,8('G+5%/)(,-'(%5>8$/,-="
?$%&:',"
DM" K%$'),-'./0'('C'$4($%;(5/.," MD" I.'(')*N8<N5/)'(&8=='),.(,8(+8/),(89,(.9?,5',/'.(%)*(8**/,/'."
@" A8)B,(.'+%$%,'(.9?$89,/)'(8$(C%$/%?5'()%='.(<$8=(,-'(<8558;/)>(
FO" I.'(,%?5'N588:9+(,8(,'.,(<8$(='=?'$.-/+(/)(5/.,.(8<(.,$/)>.[(9.'(+),%&' MF" S8=='),(%)4,-/)>(,-%,(-%.(+9005'*(8$(,$/&:'*(489"
8+')/)>(?$%&:',"
<8$(='=?'$.-/+(8<(5/.,.(8<(%)4,-/)>('5.'" MH" S8)./*'$(;-',-'$(/,B.(?',,'$(,8($';$/,'(,-%)(,8(&8=='),"
D" A8)B,(9.'(9))'&'..%$4(+%$'),-'.'.(<8$(?9/5,/).(%)*(E-8)8$%$4B(
MJ" I.'(E/)C/./?5'B(K_A(.'&,/8).(<8$(58)>'$(,'&-)/&%5(*/.&9../8)."
?9/5,/)."
F" 7'+%$%,'(&8=+5'G(:'4.(8$(/)*/&'.(<$8=(,-'/$(.9$$89)*/)>(?$%&:',." Variables ML" S-'&:(,-'(.+'55/)>Q(.4),%GQ(%)*(.%)/,4(8<(489$(*8&9='),%,/8)"
H" I.'(;-/,'.+%&'(,8(-'5+(?/)%$4(8+'$%,8$.(.,%)*(89,(<$8=(,-'/$( F!" TC8/*(9./)>()8)N5'G/&%5(C%$/%?5'."
8+'$%)*." F6" A8)B,(9.'(+%&:%>'(C%$/%?5'.(/)(489$(8;)(*'C'58+='),"
Built-in Functions
J" K5%&'(%(.'=/&858)(%<,'$('C'$4(.,%,'=')," F@" P<(489B$'(<8$&'*(,8(=8*/<4(%(+%&:%>'(C%$/%?5'Q("('+"/0'(/," MM" A8)B,($'&8=+9,'(.8$,(:'4.(/)./*'(%(#(%*"
L" K5%&'(%(&8==%(%<,'$('C'$4(C%59'(/)(%(=95,/5/)'(5/.," !OO" I.'(%!8!%#!(,8($'C'$.'(%(5/.,"
FD" P)/,/%5/0'(%)4(C%$/%?5'(489("('+"/0'"
M" I.'(JLN&859=)(5/)'."
FF" -#!./)0"1#2(<8$(,-'(5'..(<%=/5/%$(+9)&,9%,/8)(C%$/%?5'." !O!" I.'(.&%5%$(%!8!%#!(,8($'C'$.'(%(.&%5%$"
!O" I.'(<89$N&859=)(/)*'),%,/8)(5'C'5." !"#$ %&'(')*+',(*+'(!"##$%&'(-./01'(.,(*+'(*+,''23,40-'5*(6.,-(.6(/0'(/," !N"$ X3='(63)1'/(D0)1*)5&(*+,.;('A<'B*).5&(*..$ "!K$ Y39'(3**,)D0*'&()5)*)31)V'/(35/(9',)6)'/(30*.-3*)<311C$
FH" P<(489B$'(<8$&'*(,8(=8*/<4(%(+9)&,9%,/8)(C%$/%?5'Q("('+" !O6" I.'(-)5+'9 (,8('G,$%&,(</G'*N;/*,-(</'5*."
!!" P)*'),(;/,-(.+%&'.Q()8,(,%?." !"#$$ A8)B,(9.'(,-'($'>'G(=%,&-(C%$/%?5'." !N>$ X3='(63)10,'&(63*31()5(311(<.5*'A*&$ "!M$ IB'<)6C(<.',<).5&(3&(#/3C!5J!$K:(#5LMNC!$K:(35/(#O""P!$K(-'*+./&$
!6" R'C'$(+5%&'(,;8(.,%,'='),.(8)(,-'(.%='(5/)'" FJ" !O@" I.'(#5"1*(,8('G,$%&,(./=+5'(C%$/%?5'N;/*,-(</'5*."
!"7$ 8'9',(!"#$:(%&!'#:(.,("()$*(*.(3(6)1'(;)*+.0*(<+'<=)54(*+'(.0*<.-'$ !NJ$ T'(<3,'601(;+'5(*'&*)54(6.,(63)10,'(.6(*+'('2'*#3(D0)1*)5$
FL" #';%$'(8<(%)4(=8*/</&%,/8)(C/%(()" !OD" I.'(*+,-../01)20(,8('G,$%&,(&8=+5'G(C%$/%?5'N;/*,-(</'5*." "!N$ %&'(#;LMLP@3!QN(-'*+./&()5&*'3/(.6(/L,NC##(<311&$
!@" S8*'(/)(+%$%>$%+-." "!#$ O.5P*(0&'(@L3"P"@4(+$
!>?$ FM" I.'()'>%,/C'(/)*/&'.(;-')(&89),/)>(<$8=(,-'(')*(8<(%)(%$$%4" !NK$ U+,.;('A<'B*).5&(.5(311(63)10,'&:()5<10/)54(,'<.9',3D1'(.5'&$
@1.&'(6)1'+35/1'&('AB1)<)*1C:(35/(3&(&..5(3&(B.&&)D1'$ !OF" TC8/*(.,$/)>(!8+""
!D" A8)B,(&9**5'(%)(!"#!" !>!$ %&'(+,)&#(()*+:(5.*(-!((()*+$ !NM$ Y39'('A<'B*).5&(,'B.,*(6,.-(*+'(<311',Z&(1.<3*).5:(5.*(6,.-(*+'(B13<'(
HO" %:'(%*C%),%>'(8<(-%.-(%)*(%$$%4(.5/&/)>" !OH" S8)./*'$(?9/5*/)>(489$(.8$,/)>($89,/)'.(;/,-(034-..567+4"
!F" T5/>)(&8$$'.+8)*/)>(/,'=.(C'$,/&%554"
!H" #$'%:(58)>('G+$'../8).(?'<8$'(%)(8+'$%,8$"
!>"$ E,'6',(1)5'2D3&'/(FGH(*.(&10,B)54$
H!" I.'(%(,%?95%$(5%489,(<8$(.5/&'." ;+','(*+'C(;','(*+,.;5$
!OJ" I.'(DN%$>(#-:#*%(/).,'%*(8<(5C%59'(#-:#*%" Modules
!>>$ I10,B(3(6)1'+35/1'(;)*+(3(.!(D1.<=(6.,(B0,)*C$
H6" U%&,8$(5%$>'(:'4(8$(/)*'G(5/.,.(89,(8<(,-'/$(.5/&'." !NN$ @.-B.&'(',,.,(-'&&34'&()5(*+'(,'<)B)'5*P&(/)31'<*$
!OL" W%:'(%++$8+$/%,'(9.'(8<(5C%59'(C%59'."
!J" U%&,8$(89,(58)>('G+$'../8).(/)(,-'(=/**5'(8<(.,%,'='),." !N#$ O.<0-'5*('9',C(',,.,(-'&&34'()5(*+'(,'<)B)'5*P&(/)31'<*$ "!7$ O'&)45(*+'(-./01'P&()5*',63<'(6),&*$
!>J$ I10,B(3(&*,'3-(;)*+(,'-&.##/&0-1(6.,(B.;',(35/(&)-B1)<)*C$ !OM" I.'(0"(:Q()8,(8]$"
!L" T5;%4.(?$'%:(%(58)>('G+$'../8)(%,(,-'(8+'$%,8$(8<(,-'(58;'.,(+8../N !N7$ %&'('A<'B*).5(.D['<*&(;+'5'9',(63)10,'(/3*3(5''/&(*.(D'(<.59'C'/( ""?$ E13<'(.,)4)531(<./'()51)5'$(E13<'(/0B1)<3*'/(<./'()5(3(&0D,.0*)5'$(
!>K$ L9.)/(0&)54((2/34!5:(051'&&(C.0(,'311C(-'35()*$
?5'(+$'&'*')&'" !>M$
Control Structures
L1;3C&(B0*(6)1'+35/1'&()5(D,3<'&(;)*+)5(35C(1-%67(&*3*'-'5*$
!!O" TC8/*(%($%;(#!"!'*(<8$()8)N/),'>'$(.5''+."
*.(3(+35/1',$ E13<'(/0B1)<3*'/(&0D,.0*)5'&()5(3(-./01'$
!M" #$'%:(58)>(%../>)='),.(?'<8$'(,-'(%../>)='),(8+'$%,8$" !!!" T5;%4.(9.'(%(?58&:(;/,-(%(4+5(%)*(0%!5"
!#?$ %&'('A<'B*).5(.D['<*&(;+'5(',,.,(-'&&34'&(-3C(<+354'$ ""!$ %&'(*+,''2B3,*(9',&).5(50-D',&$
!>N$ H@" I.'(?58&:(1&Q()8,(+8.,</G(1&"
L1;3C&(B,.-B*(6.,()5*',3<*)9'()5B0*$ !!6" I.'(,-'(E)8)N?9/5,/)(?9/5,/).B"
6O" U8$=%,(&%.&%*'*(,'$)%$4(8+'$%,8$.(/)(&859=)." !#!$ %&'('A<'B*).5(.D['<*&(;+'5(*;.(.,(-.,'('A<'B*).5&(3,'(,'13*'/$ """$ 56.,<'(C.0,(9',&).5(,'^0),'-'5*&(B,.4,3--3*)<311C$
!>#$ O.5P*(,')59'5*(*+'(&*35/3,/(*'&*(6.,()5*',3<*)9)*C$
HD" 3'.'$C'(+8.,</G(1&(<8$(<58;N8<N&8),$85(.,%,'='),."
6!" K%$'),-'./0'(58)>(5/.,." !#"$ @3*<+('A<'B*).5(.D['<*&()5(-.&*2/',)9'/26),&*(.,/',$ "">$ AB.,*([0/)<).0&1C(35/:(;+','(B.&&)D1':(.51C(DC(,'^0'&*$
!>7$ %&'(*+'(A8)B,(9.'(+8.,</G(-)"!##Q(&(%Q(321"!Q(8$(-)*1""
HF" !"##,-8917(-./01'(6.,(B,.-B*)54$
66" V)<8$&'(489$(&-8.')(5%489,(.,45'(='&-%)/&%554" !J?$ L1;3C&(<.59'C(*+'(B,.4,'&&(.6(1.54(5.52)5*',3<*)9'(.B',3*).5&(
HH" A8)B,(9.'(-)"!##(8$(-)*1"(%,(%55" Subroutines
!#>$ T0)1/('A<'B*).5(<13&&'&(30*.-3*)<311C$ ""J$ @.5&)/',('AB.,*)54(/'<13,3*)9'1C$
!#J$ %5B3<=(*+'('A<'B*).5(93,)3D1'()5('A*'5/'/('A<'B*).5(+35/1',&$ 9" ""K$ 8'9',(-3='(93,)3D1'&(B3,*(.6(3(-./01'P&()5*',63<'$
;)*+)5()5*',3<*)9'(3BB1)<3*).5&$
HJ" TC8/*(SN.,45'(&(%(.,%,'='),." !!@" S%55(.9?$89,/)'.(;/,-(+%$'),-'.'.(?9,(;/,-89,(%(5'%*/)>(
Naming Conventions !J!$ @.5&)/',(0&)54(*+'(/9:-7##;899'67<(-./01'(*.(30*.-3*'(C.0,(
HL" TC8/*(.9?.&$/+,/)>(%$$%4.(8$(-%.-'.(;/,-/)(588+."
""M$ T0)1/(5';(-./01'(6,3-';.,=&(30*.-3*)<311C$
!!D" A8)B,(>/C'(.9?$89,/)'.(,-'(.%='()%='.(%.(?9/5,N/)(<9)&,/8)." ""N$ %&'(<.,'(-./01'&(;+','9',(B.&&)D1'$
6@" I.'(>$%==%,/&%5(,'=+5%,'.(;-')(<8$=/)>(/*'),/</'$." B,.4,'&&()5/)<3*.,&$
HM" R'C'$(.9?.&$/+,(=8$'(,-%)(8)&'(/)(%(588+" Command-Line Processing
!!F" T5;%4.(9)+%&:(:)(</$.," ""#$ %&'(@EL8(-./01'&(;+','(6'3&)D1'$
6D" R%='(?885'%).(%<,'$(,-'/$(%..8&/%,'*(,'.," !J"$ L9.)/(3(,3;('#&#%*(;+'5(&'**)54(30*.610&+'&$
JO" I.'()%='*(5'G/&%5.(%.('G+5/&/,(&(%(588+(/,'$%,8$." !!H" I.'(%(-%.-(8<()%='*(%$>9='),.(<8$(%)4(.9?$89,/)'(,-%,(-%.(=8$'(
!#K$ 56.,<'(3(&)541'(<.5&)&*'5*(<.--35/21)5'(&*,0<*0,'$
6F" W%$:(C%$/%?5'.(,-%,(.,8$'($'<'$')&'.(;/,-(%($%!&(.9<</G" J!" T5;%4.(*'&5%$'(%(&(%(588+(/,'$%,8$(C%$/%?5'(;/,-(4," ,-%)(,-$''(+%$%=','$."
!!J" I.'(6!&1)!6)'..(8$(!71#*')&'(,8(,'.,(<8$(=/../)>(%$>9='),." Testing and Debugging
!#M$ L/+','(*.(3(&*35/3,/(&'*(.6(<.59'5*).5&()5(C.0,(<.--35/21)5'(&C52
6H" R%='(%$$%4.(/)(,-'(+59$%5(%)*(-%.-'.(/)(,-'(./)>95%$" References (/).,'%*(8<(&(%(;-')(>')'$%,/)>()';(5/.,.(<$8=(85*"
J6" I.'(4+5 *3A$
6J" I.'(9)*'$.&8$'.(,8(.'+%$%,'(;8$*.(/)(=95,/;8$*(/*'),/</'$." !#N$ !!L" 3'.85C'(%)4(*'<%95,(%$>9='),(C%59'.(%.(.88)(%.(:)(/.(9)+%&:'*"""7$ Q,)*'(*+'(*'&*(<3&'&(6),&*$
J@" I.'(0%!5(%)*(&1%#*(/).,'%*(8<(&(%(;-')(.'%$&-/)>(<8$(C%59'.(/)(%(5/.," I*35/3,/)V'(C.0,(-'*32.B*).5&$
!J>$ Q+','9',(B.&&)D1':(/','6','5<'(;)*+(3,,.;&$ !!M" T5;%4.($',9$)(.&%5%$(/)(.&%5%$($',9$)."
6L" A/.,/)>9/.-(*/<<'$'),(+$8>$%=(&8=+8)'),.(?4(&%.'" JD" I.'(&(%(/).,'%*(8<(4+5(;-')(,$%).<8$=/)>(%(5/.,(/)(+5%&'" !##$ L11.;(*+'(&3-'(6)1'53-'(*.(D'(&B'<)6)'/(6.,(D.*+()5B0*(35/(.0*B0*$ ">?$ I*35/3,/)V'(C.0,(*'&*&(;)*+(3'<7##/%91&'(.,(3'<7##M8-'$
!JJ$ Q+','(B,'6)A(/','6','5<)54()&(0539.)/3D1':(B0*(D,3<'&(3,.05/(*+'( !6O" W%:'(5/.,N$',9$)/)>(.9?$89,/)'.($',9$)(,-'(E8?C/89.B(C%59'(/)(.&%5%$( I*35/3,/)V'(C.0,(*'&*(&0)*'&(;)*+(3'<7##R:-6'<<$
6M" T??$(/*'),.(?4(+$'<G" JF" I.'(%(.9?$89,/)'(&%55(,8(<%&,8$(89,(&8=+5'G(5/.,(,$%).<8$=%,/8)." !#7$ I*35/3,/)V'(.5(3(&)541'(3BB,.3<+(*.(<.--35/21)5'(B,.<'&&)54$ ">!$
,'6','5<'$ &8),'G,"
@O" T??$'C/%,'(8)54(;-')(,-'(='%)/)>($'=%/).(9)%=?/>989." JH" R'C'$(=8*/<4(()(/)(%(5/.,(<9)&,/8)" !7?$ 5&0,'(*+3*(C.0,()5*',63<':(,052*)-'(-'&&34'&:(35/(/.<0-'5*3*).5( ">"$ Q,)*'(*'&*(<3&'&(*+3*(63)1$
!JK$ 8'9',(0&'(&C-D.1)<(,'6','5<'&$ !6!" Y-')(,-'$'(/.()8(E8?C/89.B(.&%5%$(&8),'G,($',9$)(C%59'Q(&8)./*'$(
@!" TC8/*(9./)>(/)-'$'),54(%=?/>989.(;8$*.(/)()%='." JJ" TC8/*(&%.&%*/)>(%)(1&" ,'-3)5(<.5&)&*'5*$ ">>$ U'&*(D.*+(*+'(1)='1C(35/(*+'(051)='1C$
!JM$ %&'(+#/0#$(*.(B,'9'5*(<),<013,(/3*3(&*,0<*0,'&(6,.-(1'3=)54(-'-.,C$ /3;-+,-<6=..>+-<4;(/).,'%*"
@6" K$'</G(E<8$(/),'$)%5(9.'(8)54B(.9?$89,/)'.(;/,-(%)(9)*'$.&8$'" JL" I.'(,%?5'(588:N9+(/)(+$'<'$')&'(,8(&%.&%*'*('Z9%5/,4(,'.,." !7!$ W3<*.,(.0*(<.--.5(<.--35/21)5'()5*',63<'(<.-B.5'5*&()5*.(3( ">J$ L//(5';(*'&*(<3&'&(D'6.,'(C.0(&*3,*(/'D044)54$
JM" Y-')(+$8*9&/)>(%(C%59'Q(9.'(,%?95%$(,'$)%$/'." !66" A8)B,(9.'(.9?$89,/)'(+$8,8,4+'."
&+3,'/(-./01'$ ">K$ L1;3C&(4'#5'*()%*$
Values and Expressions RegularA8)B,(9.'(6(]321"!(588+."
LO" Expressions !6@" T5;%4.($',9$)(C/%(%)('G+5/&/,(%!*-%)" ">M$ L1;3C&(*0,5(.5(;3,5)54&('AB1)<)*1C$
!6D" I.'(%(?%$'(%!*-%)(,8($',9$)(<%/59$'" ">N$ 8'9',(3&&0-'(*+3*(3(;3,5)5426,''(<.-B)13*).5()-B1)'&(<.,,'<*5'&&$
L!" 3'^'&,(%.(=%)4(/,'$%,/8).(%.(+8../?5'Q(%.('%$54(%.(+8../?5'"
!JN$ L1;3C&(0&'(*+'(=>(6134$
@@" I.'(/),'$+85%,/)>(.,$/)>(*'5/=/,'$.(8)54(<8$(.,$/)>.(,-%,(%&,9%554(/),'$N L1;3C&(0&'(*+'(=9(6134$ Objects ">#$ U0,5(.66(&*,)<*0,'&(.,(;3,5)54&('AB1)<)*1C:(&'1'<*)9'1C:(35/()5(*+'(
!J#$ L6" A8)B,(&8),8$,(588+(.,$9&,9$'.(^9.,(,8(&8).85/*%,'(&8),$85"
+85%,'"
@D" A8)B,(9.'(!!(8$(""(<8$(%)('=+,4(.,$/)>"
L@" I.'(&(%(%)*(%!6((/).,'%*(8<(%)(/$$'>95%$54(&89),'*(321"!"
!J7$ %&'(?@(35/(?A(3&(&*,)54(D.05/3,C(35<+.,&$ I/O
!7"$ X3='(.D['<*(.,)'5*3*).5(3(<+.)<':(5.*(3(/'6301*$ &-311'&*(B.&&)D1'(&<.B'$
LD" X%?'5('C'$4(588+(,-%,(/.('G/,'*('G+5/&/,54Q(%)*(9.'(,-'(5%?'5(;/,-(!7>$ @+..&'(.D['<*(.,)'5*3*).5(0&)54(3BB,.B,)3*'(<,)*',)3$
!K?$ %&'(?A:(5.*(?B:(*.()5/)<3*'(R'5/(.6(&*,)54P$ ">7$ _'3,5(3*(1'3&*(3(&0D&'*(.6(*+'(B',1(/'D044',$
@F" A8)B,(;$/,'(8)'N&-%$%&,'$(.,$/)>.(/)(C/.9%554(%=?/>989.(;%4." !K!$ L1;3C&(0&'(*+'(=<(6134$ !6F" A8)B,(9.'(?%$';8$*(</5'-%)*5'."
!7J$ O.5P*(0&'(B&'0/.+3&+'&$ "J?$ %&'(&',)31)V'/(;3,5)54&(;+'5(/'D044)54(R-350311CP$
'C'$4()!7*Q("+#*Q(8$(%!6(" !6H" I.'(/)*/$'&,(</5'-%)*5'."
@H" I.'()%='*(&-%$%&,'$('.&%+'.(/).,'%*(8<()9='$/&('.&%+'." !K"$ @.5&)/',(-35/3*)54(*+'(C'D'>1##@078E&:D<(-./01'$ !7K$ O.5P*(0&'(,'&*,)<*'/(+3&+'&$ "J!$ @.5&)/',(0&)54(R&-3,*(<.--'5*&P(;+'5(/'D044)54:(,3*+',(*+35(
@J" I.'()%='*(&8).,%),.Q(?9,(*8)B,(9.'('()#*+)*" !6J" P<(489(-%C'(,8(9.'(%(+%&:%>'(</5'-%)*5'Q("('+"/0'(/,(</$.,"
!7M$ L1;3C&(0&'(6011C('5<3B&013*'/(.D['<*&$ +/($(&*3*'-'5*&$
!K>$ %&'(9FSG()5(B,'6','5<'(*.(=S=()5(-01*)1)5'(,'4'A'&$
@L" A8)B,(+%*(*'&/=%5()9=?'$.(;/,-(5'%*/)>(0'$8." !KJ$ O.5P*(0&'(35C(/'1)-)*',&(.*+',(*+35(=S=(.,(9FSG$ !7N$ ])9'('9',C(<.5&*,0<*.,(*+'(&3-'(&*35/3,/(53-'$
!KK$ E,'6',(&)54013,(<+3,3<*',(<13&&'&(*.('&<3B'/(-'*3<+3,3<*',&$ !7#$ O.5P*(1'*(3(<.5&*,0<*.,(<1.5'(.D['<*&$
!77$ L1;3C&(B,.9)/'(3(/'&*,0<*.,(6.,('9',C()5&)/'2.0*(<13&&$
Miscellanea
!KM$ E,'6',(53-'/(<+3,3<*',&(*.('&<3B'/(-'*3<+3,3<*',&$
"??$ Q+'5(<,'3*)54(-'*+./&:(6.11.;(*+'(4'5',31(40)/'1)5'&(6.,(&0D,.02 "J"$ %&'(3(,'9)&).5(<.5*,.1(&C&*'-$
!KN$ E,'6',(B,.B',*)'&(*.('50-',3*'/(<+3,3<*',(<13&&'&$
*)5'&$ "J>$ F5*'4,3*'(5.52E',1(<./'()5*.(C.0,(3BB1)<3*).5&(9)3(*+'(!6&%6'##S
!K#$ @.5&)/',(-3*<+)54(3,D)*,3,C(;+)*'&B3<':(,3*+',(*+35(&B'<)6)<(;+)*'&2
"?!$ E,.9)/'(&'B3,3*'(,'3/(35/(;,)*'(3<<'&&.,&$ -./01'&$
B3<'(<+3,3<*',&$
"?"$ O.5P*(0&'(19310'(3<<'&&.,&$ "JJ$ `''B(C.0,(<.56)40,3*).5(1354034'(05<.-B1)<3*'/$
!K7$ T'(&B'<)6)<(;+'5(-3*<+)54(R3&(-0<+(3&(B.&&)D1'P$
!M?$ %&'(<3B*0,)54(B3,'5*+'&'&(.51C(;+'5(C.0()5*'5/(*.(<3B*0,'$ "?>$ O.5P*(0&'(*+'()5/),'<*(.D['<*(&C5*3A$ "JK$ O.5P*(0&'(-!(3/*&$
!M!$ %&'(*+'(50-',)<(<3B*0,'(93,)3D1'&(.51C(;+'5(C.0P,'(&0,'(*+3*(*+'( "?J$ E,.9)/'(35(.B*)-31()5*',63<':(,3*+',(*+35(3(-)5)-31(.5'$ "JM$ O.5P*(*)#(93,)3D1'&(.,(6)1'+35/1'&$
B,'<'/)54(-3*<+(&0<<''/'/$ "?K$ H9',1.3/(.51C(*+'()&.-.,B+)<(.B',3*.,&(.6(314'D,3)<(<13&&'&$ "JN$ O.5P*(D'(<1'9',$
!M"$ L1;3C&(4)9'(<3B*0,'/(&0D&*,)54&(B,.B',(53-'&$ "?M$ L1;3C&(<.5&)/',(.9',1.3/)54(*+'(D..1'35:(50-',)<:(35/(&*,)54(<.',2 "J#$ F6(C.0(-0&*(,'1C(.5(<1'9',5'&&:('5<3B&013*'()*$
!M>$ U.='5)V'()5B0*(0&)54(*+'(=DH(6134$ <).5&(.6(.D['<*&$ "J7$ O.5P*(.B*)-)V'(<./'(a(D'5<+-3,=()*$
!MJ$ T0)1/(,'4013,('AB,'&&).5&(6,.-(*3D1'&$ "K?$ O.5P*(.B*)-)V'(/3*3(&*,0<*0,'&(a(-'3&0,'(*+'-$
!MK$ T0)1/(<.-B1'A(,'4013,('AB,'&&).5&(6,.-(&)-B1',(B)'<'&$ Class Hierarchies "K!$ _..=(6.,(.BB.,*05)*)'&(*.(0&'(<3<+'&$
"K"$ L0*.-3*'(C.0,(&0D,.0*)5'(<3<+)54$
!MM$ @.5&)/',(0&)54(C'D'>1##;89986()5&*'3/(.6(;,)*)54(C.0,(.;5(
"?N$ O.5P*(-35)B013*'(*+'(1)&*(.6(D3&'(<13&&'&(/),'<*1C$ "K>$ T'5<+-3,=(35C(<3<+)54(&*,3*'4C(C.0(0&'$
,'4'A'&$
"?#$ %&'(/)&*,)D0*'/('5<3B&013*'/(.D['<*&$ "KJ$ O.5P*(.B*)-)V'(3BB1)<3*).5&(a(B,.6)1'(*+'-$
!MN$ L1;3C&(0&'(<+3,3<*',(<13&&'&()5&*'3/(.6(&)541'2<+3,3<*',(31*',53*).5&$
"?7$ 8'9',(0&'(*+'(.5'23,40-'5*(6.,-(.6(D1'&&$ "KK$ T'(<3,'601(*.(B,'&',9'(&'-35*)<&(;+'5(,'63<*.,)54(&C5*3A$
!M#$ W3<*.,(.0*(<.--.5(366)A'&(6,.-(31*',53*).5&$
"!?$ E3&&(<.5&*,0<*.,(3,40-'5*&(3&(13D'1'/(9310'&:(0&)54(3(+3&+(,'6',2
!M7$ E,'9'5*(0&'1'&&(D3<=*,3<=)54$
'5<'$ !"#$%&"'(%!#)*(+*"'%,"-"#".*"%/0+1"%2"#'+3.%45645665
!N?$ E,'6',(6)A'/2&*,)54(#1(<.-B3,)&.5&(*.(6)A'/2B3**',5(,'4'A(-3*<+'&$ "!!$ O)&*)540)&+(3,40-'5*&(6.,(D3&'(<13&&'&(DC(<13&&(53-'(3&(;'11$ !"#$%&"'(%!#)*(+*"'%78%,)-+).%/0.1)2
"!"$ I'B3,3*'(C.0,(<.5&*,0<*).5:()5)*)31)V3*).5:(35/(/'&*,0<*).5(B,.<'&&'&$ 9%:66;%<=,"+$$8%>"1+)%?.*5@%A$$%#+BC('%#"'"#2"15
Error Handling "!>$ T0)1/(*+'(&*35/3,/(<13&&()56,3&*,0<*0,'(30*.-3*)<311C$ 3"4"#".*"%56+7"%78%809).%:#0-).'
!N!$ U+,.;('A<'B*).5&()5&*'3/(.6(,'*0,5)54(&B'<)31(9310'&(.,(&'**)54(6134&$ "!J$ %&'(;&:<<##/7I(*.(30*.-3*'(*+'(/'311.<3*).5(.6(3**,)D0*'(/3*3$ 9%:66D%EF0+##"$%G3.'0$().*8@%A$$%#+BC('%#"'"#2"15

• Perl::Tidy - “Parses and beautifies perl
source”
• Perl::Critic - “Critique Perl source code for
best-practices”

Perl::Tidy
use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

Perl::Tidy
use strict;
my @list = ( 'Emacs', 'Vi ' );
my $rand = rand();
print "10 random users said:n";
foreach ( 0 .. 10 ) {
my $i = int( $rand + rand() );
print " $list[$i] users are from Venus" . ", "
. "$list[1-$i] users are from Mars" . "n";
}

Perl::Tidy
• configurable (parameters or .perltidyrc)
• integrates with most text editors
• some people use it as an svn hook

Perl::Critic
use strict;
my @list=('Emacs', 'Vi '); my $rand = rand();
print "10 random users said:n";
foreach(0..10) {
my $i=int ($rand+rand());
print " $list[$i] users are from Venus" . ", " .
"$list[1-$i] users are from Mars" .
"n";
}

Perl::Critic
Loop iterator is not lexical at line 5, column 1.
See page 108 of PBP. (Severity: 5)

Perl::Critic
• configurable (several severity levels,
extendable, .perlcriticrc)
• integrates with most text editors
• some people also use it as an svn hook
• if you don’t own PBP, there’s also user-
contributed documentation on each subject

Methods
• Pair programming
• Code review

Further documentation
• http://127h.sl.pt - An Introduction to Perl
Critic, by Josh McAdams
• http://127i.sl.pt - Perl Tidy Perl Critic, by
olegmmiller
• http://127w.sl.pt - Perl Best Practices
Reference Guide