Introduction to Perl Programming

Introduction to Perl Introduction to Perl ProgrammingProgramming

Introduction to Perl Introduction to Perl ProgrammingProgramming

Morris LawMorris Law

December 8, 2012December 8, 2012

Content• What is PERL?• Installation and usage of PERL on Windows• PERL number and strings• Scalar, array and hash• Operators• Control Flow• Regular Expression• Subroutine• File• Use of Perl Package Manager

What is PERL?• Practical Extraction and Report Language• more than 1 way to do it• easy for human reading• highly portable• talk text• high level language• free• program code with .plx and .pl as extension

on MS Windows and UNIX respectively

What is PERL?• interpreter as well as compiler• support unicode• base 16 (hex)• bundle with help:-

– perldoc -f print (info)– perldoc -q reverse (faq)– perldoc Text::Wrap

PERL is free and portable

• Most UNIX/Linux distribution come with PERL installed

• Mac OS X already has PERL installed• Windows does not come with PERL by

default. Two choices– ActiveState PERL– Strawberry PERL

• Latest stable version is 5.16.2

Install and run ActiveState PERL

• Download from http://www.activestate.com/activeperl/downloads

• Run PERL Package Manager (PPM) to install and update standard and additional packages

• Start a command line interface (cmd)• Prepare PERL source code (e.g. a.plx)• Run by > perl a.plx

Install and run DWIMPERL based on Strawberry

PERL• Download from

http://dwimperl.com/windows.html

• Come with Padre, the Perl IDE

PERL numbers• Number

– 255 (decimal)– 0377 (octal)– 0b1111111 (binary)– 0xFF (hexidecimal)

• Example#!/usr/bin/perl#goodnums.plxuse warnings;print 255, "\n";print 0377, "\n";print 0b11111111, "\n";print 0xFF, "\n";

goodnums.plx

PERL Strings• single-quoted with no processing

print '\t This is a $test \n';

• double-quoted with interpolation$test = "mid term test";print "\t This is a $test \n";

• here-documentprint<<EOF;

Dear Mary, I am demonstrating the usage of PERL

EOF

PERL operators• Arithmetics

+,-,*,/,( ), **, %

• Bitwise&, |, ^, ~

• Comparison==, !=, <, >, >=, <=<=>gt, ge, eq, lt, le, cmp

• Boolean&&, ||, !

• Repetitionx3, x4

PERL operators (cont.)• Ternary operator

a ? b : c

• Range operator…

• Shift<<, >>

• regular expression=~, !~a <opr>= b where <opr> = +,-,*,\,/

PERL scalar variables ($)

• scalar ($)– $user, $User, $b56, $_

my $name = "fred";

my $salutation = "Dear $name, ";

print $salutation, "\n";

my $time = 8;

print "This is my ${time}th time \n";

– Standard Input <STDIN>– Standard Output <STDOUT>

PERL array variable (@)• array (@)

@x = (12, 34, 56);@array2 = qw/One Two Three Four/;@a = qw(Mon Tue Wed Thu Fri Sat Sun);($mone, $mtwo) = (1, 3);($mone, $mtwo) = ($mtwo, $mone);$a = (10, 20, 30)[0]; # 10$a = @a[2]; # Wedfor $day (@a) { print $day , "\t";}for (0 … $#array2) {print "Hello World\n"}

for (@x){$_*= 2} print "After : @x\n";

array2.plx

Use of pop and push in array

• pop : remove the top element of an array

• push : add elements to the top of array

@a = (1 ... 6);

@b = reverse (1 ... 6);

push @a,@b;

print @a;

pop @a;

print @a;

reverse1.plx

operators behaviour• functions behave differently with

operators• take sort as an example

# sort1.plx

my @unsorted = (1, 2, 11, 24, 3, 36, 40, 4);

my @string = sort {$a cmp $b} @unsorted;

print "String sort: @string \n";

my @number = sort {$a <=> $b} @unsorted;

print "Number sort: @number \n";

PERL Hash variable (%)• Hash : associative array

@array = ("Gary", "Dallas", "Lucy", "Exeter", "Ian", "Reading", "Samantha", "Oregon");

%where = @array;## %where = (Gary => "Dallas", Lucy => "Exeter", Ian =>

"Reading", Samantha => "Oregon");#%who = reverse (%where);## %who = (Dallas => "Gary", Exeter => "Lucy", Reading =>

"Ian", Oregon => "Samantha"#print $where{Gary}, "\n";print $who{Reading}, "\n";delete $where{Lucy};$where{Eva} = "Denver";for (keys %where) { print "$_ lives in $where{$_}\n"}%who = reverse (%where);print $who{Denver};print $where{Eva};

hash1.plx

PERL control flow• if { … } elsif { … } else { … }

#guess.plx$password = '1234';my $guess = <STDIN>;chomp $guess;if ($password ne $guess) { die "Go away, imposter!\n";} else { die "Correct password!\n";}

• unless ( <condition> ) { die “message” }# rate1.plx%currency = ( China => "RMB", Japan => "Yen", UK => "Pound", US => "Dollar" );%rate = (RMB => 0.8, Yen => 10, Pound => 15, Dollar => 7.8);$to = <STDIN>;chomp $to;unless (exists $rate{$to}) { die "I don't know anything about ${to} as a currency\n";}# exists ($rate{to}) or die "I don't know anything about ${to} as a currency\n" print "The exchange rate of $to is $rate{$to}!";

guess.plx, rate1.plx

PERL control flow (cont)

• while ( <condition> ) { <action> }• do { <action> } while (<condition> );• for ( <loop range> ) { <action> }

#testfor1.plxprint "Enter number (1-3) : "; my $choice = <STDIN>;chomp $choice;for ($choice) { $_ == 1 && print "You chose number ONE\n"; $_ == 2 && print "You chose number TWO\n"; $_ == 3 && print "You chose number THREE\n";}

testfor1.plx

PERL control flow (cont)

• foreach# foreach1.plxuse strict;my @collection = qw/hat shoes shirts shorts/;foreach my $item (@collection) {print "$item\n";}

# foreach2.plxuse strict;my %table = qw/schmoe joe smith john simpson bart/;my($key, $value); # Declare two variables at oncewhile ( ($key, $value) = each(%table) ) { print "$key and $value are friend\n";}

Regular Expression• RE use to describe patterns in text

– a* represent zero or more ‘a’.• the * character (repeat)

– ba* will match ba, baab, baaac, bc• the . character (any)

– a.c will match a, a c, amc, abc, aac, apc, • the | character (or)

– abc|xyz will match abc or xyz• group with ()

– xx(abc|xyz)*xx will match xxabcxx, xxxyzxx, xxabcxyzxx, etc.

RE – anchor and pattern matching

• ^a match the line preceding with a• z$ match the line end with z• What does ^aa*$ match?• guess how ^a.*[0-9]$ match?• test with the following

use strict;while ( defined($currentLine = <STDIN>) ) { if ($currentLine =~ /^aa*$/) { print $currentLine; }}

PERL subroutine• Usually PERL subroutine come in first capital• Run with or without preceding &.

use strict;sub HowdyEveryone {print "Hello guys.\nWhere do you want to go with Perl today?\n";}&HowdyEveryone

• Run a subroutine with argumentuse strict;sub HowdyEveryone {my($name1, $name2) = @_;return "Hello $name1 and $name2.\n" ."Where do you want to go with Perl today?\n";}print &HowdyEveryone("bart", "lisa");

PERL subroutine• subroutine accept as many arguments

# greeting3.plxuse strict;sub HowdyEveryone {my($greeting, @names) = @_;my $returnString;foreach my $name (@names) {$returnString .= "$greeting, $name!\n";}return $returnString ."Where do you want to go with Perl today?\n";}print &HowdyEveryone("How is", "bart", "lisa", "homer",

"marge", "maggie");

PERL file# numbering lines# nl.plxuse warnings;use strict;

open FILE, "example.txt" or die $!;my $lineno = 1;

while (<FILE>) { print $lineno++; print ": $_";}

nl.plx

Perl file• A special notation <> stands for <ARGV>, argument input

# Accept multiple files# nl2.plxuse warnings;use strict;

my $lineno = 1;

while (<>) { print $lineno++; print ": $_";}

• Run it with perl nl2.plx example.txt

nl2.plx

Perl file# nl3.plxuse warnings;use strict;my $lineno;my $current = "";

while (<>) { if ($current ne $ARGV) { $current = $ARGV; print "\n\t\tFile: $ARGV\n\n"; $lineno=1; } print $lineno++; print ": $_";}

nl3.plx

PERL input record separator $/

# fortune.plxuse warnings;use strict;

$/ = "\n%\n"; # input record separator

open QUOTES, “bible.txt" or die $!;my @file = <QUOTES>;

my $random = rand(@file);my $fortune = $file[$random];chomp $fortune;

print $fortune, "\n";

fortune.plx

PERL file input & output# copy.plxuse warnings;use strict;

my $source = shift @ARGV;my $destination = shift @ARGV;open IN, $source or die "Can't read source file $source: $!\

n";open OUT, ">destination" or die "Can't write on file

$destination: $!\n";

print "Copying $source to $destination\n";while (<IN>) { print OUT $_;}

copy.plx

More resources from More resources from CPANCPAN

More resources from More resources from CPANCPAN

using CPAN Explorer in DWIMusing CPAN Explorer in DWIM

Thanks!Thanks!Thanks!Thanks!Any questions?Any questions?

morris@hkbu.edu.hkmorris@hkbu.edu.hk