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

Install and run ActiveState PERL Download from 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 Come with Padre, the Perl IDE

PERL numbers Number –255 (decimal) –0377 (octal) –0b (binary) –0xFF (hexidecimal) Example #!/usr/bin/perl #goodnums.plx use warnings; print 255, "\n"; print 0377, "\n"; print 0b , "\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 = b where = +,-,*,\,/

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 –Standard Output

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

Use of pop and push in array pop : remove the top element of an array push : add elements to the top of = (1... = reverse (1... 6); push reverse1.plx

operators behaviour functions behave differently with operators take sort as an example # sort1.plx = (1, 2, 11, 24, 3, 36, 40, 4); = sort {$a cmp print "String \n"; = sort {$a print "Number \n";

PERL Hash variable (%) Hash : associative = ("Gary", "Dallas", "Lucy", "Exeter", "Ian", "Reading", "Samantha", "Oregon"); %where # # %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 = ; chomp $guess; if ($password ne $guess) { die "Go away, imposter!\n"; } else { die "Correct password!\n"; } unless ( ) { 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 = ; 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 ( ) { } do { } while ( ); for ( ) { } #testfor1.plx print "Enter number (1-3) : "; my $choice = ; 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; = qw/hat shoes shirts shorts/; foreach my $item { print "$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 ^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($currentLine = ) ) { if ($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 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 $returnString; foreach my $name { $returnString.= "$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 ( ) { print $lineno++; print ": $_"; } nl.plx

Perl file A special notation <> stands for, 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 $random = my $fortune = $file[$random]; chomp $fortune; print $fortune, "\n"; fortune.plx

PERL file input & output # copy.plx use warnings; use strict; my $source = my $destination = 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 ( ) { print OUT $_; } copy.plx

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