Introduction to Perl Programming

Introduction to Perl Programming Morris Law December 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.plx use 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-document print<<EOF; Dear Mary, I am demonstrating the usage of PERL EOF

PERL operators • Arithmetics +,-,*,/,( ), **, % • Bitwise &, |, ^, ~ • Comparison ==, !=, <, >, >=, <= <=> gt, ge, eq, lt, le, cmp • Boolean &&, ||, ! • Repetition x3, 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]; # Wed for $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.plx print "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.plx use strict; my @collection = qw/hat shoes shirts shorts/; foreach my $item (@collection) { print "$item\n"; } # foreach2.plx use strict; my %table = qw/schmoe joe smith john simpson bart/; my($key, $value); # Declare two variables at once while ( ($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 • â match the line preceding with a • z$ match the line end with z • What does âa*$ match? • guess how â.*[0-9]$ match? • test with the following use strict; while ( defined($currentLine = <STDIN>) ) { if ($currentLine =~ /âa*$/) { 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 argument use 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.plx use 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.plx use 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.plx use warnings; use strict; my $lineno = 1; while (<>) { print $lineno++; print ": $_"; } • Run it with perl nl2.plx example.txt nl2.plx

Perl file # nl3.plx use 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.plx use 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.plx use 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 CPAN using CPAN Explorer in DWIM

Thanks! Any questions? morris@hkbu.edu.hk

Introduction to Perl Programming