Perl Golf

Let’s Golf Thursday, May 3, 12

About Me • Ynon Perek • http://ynonperek.com • http://speakerdeck.com/u/ ynonperek

Thursday, May 3, 12

The Game A Competition to find the shortest — fewest

keystrokes perl code to solve a given problem Thursday, May 3, 12

The Rules • Count keystrokes (newlines matter) • No modules

• No external tools Thursday, May 3, 12

Why Golf ? Thursday, May 3, 12

Example: Head use strict; use warnings; use v5.14; my $counter

= 0; while (<>) { $counter += 1; print; last if $counter > 10; } Thursday, May 3, 12

We Can Do Better while (<>) { print; last if

$. > 10; } Thursday, May 3, 12

Yet a golfer would • Remember perl opts: -pe •

Remember range operator Thursday, May 3, 12

Yet a golfer would #!/usr/bin/perl -pe last if $. >

10 Thursday, May 3, 12

Yet a golfer would perl -pe '11..exit' Thursday, May 3,

12

And a true golfer... perl -pe '11..&' Thursday, May 3,

12

Some More Tricks • y///c Abigail’s length horror • $_

x= Larry’s boolean • }{ Abigail’s END for -pe • $\ Van-der Pijll print Thursday, May 3, 12

Challenge • Use previous tricks to print: • characters count

• words count • line count Thursday, May 3, 12

Challenge # Characters count perl -lpe '$\+=y///c}{' # Words count

perl -lpe '$\+=split}{' # Lines count perl -pe '$\=$.}{' Thursday, May 3, 12

Example: tail • Tail is harder, because we need to

remember previous lines • Can use an array Thursday, May 3, 12

Example: tail # tail using an array perl -e '@a=<>;print

@a[-10..-1]' Thursday, May 3, 12

Example: tail # Removing the array perl -e 'print ((<>)[-10..-1])'

Thursday, May 3, 12

Example: tail # Removing the array perl -e 'print ((<>)[-10..-1])'

Surprisingly, A true hacker can do better Thursday, May 3, 12

Example: tail # Recall the ~ perl -e 'print+(<>)[~9..-1]' Surprisingly,

A true hacker can do better Thursday, May 3, 12

Some More Tricks • $= Holds only int values. $==10/3

is the same as int(10/3) • $- Holds only positive values Thursday, May 3, 12

Example: $- perl -pe '$-=eval or&' 10+20 20+3 30-10 40-50

-5 1 4 5 Thursday, May 3, 12

Golf Classics • Find all anagrams in a word list.

• An anagram is two words made up of the same letters • Example: underflow - wonderful Thursday, May 3, 12

Anagrams #!/usr/bin/perl sub normalized { my ($word) = @_; my

@letters = split //, $word; return join '', sort @letters; } while (<>) { chomp; my $letters = normalized( $_ ); $words{ $letters } ||= []; push $words{ $letters }, $_; } print "@$_\n" for grep { @$_ > 1} values %words; Thursday, May 3, 12

Anagrams • Remove the sub • Prefer text over array-refs

• Prefer switches over code • Use short variable names Thursday, May 3, 12

Anagrams #!/usr/bin/perl -ln $w{ join '', sort split // }

.= "$_ "; }{ print for grep / ./, values %w; Thursday, May 3, 12

Anagrams • No need to join hash keys • Can

use regexp instead of split • Can use regexp instead of grep • Can use %h instead of values %h Thursday, May 3, 12

Anagrams #!/usr/bin/perl -ln $w{ 1, sort/./g } .= "$_ ";

}{/ ./&&print for %w; Thursday, May 3, 12

Golf Classic sub b{[@b=(abs||No,bottle."s"x!!++$_,of,beer),on,the,wall]} print "@{+b},\n@b,\nTake one down, pass it

around,\n@{+b}.\n" for-pop||-99..-1 99 bottles of beer on the wall, 99 bottles of beer, Take one down, pass it around, 98 bottles of beer on the wall. Thursday, May 3, 12

Non-perl Golf • http://vimgolf.com/ • http://codegolf.com/ Thursday, May 3, 12

What’s Next • Go to http:// terje2.frox25.no- ip.org/ • Download

the book Thursday, May 3, 12