Perl Introduction

1. Perl Welcome Pratical Extraction and Reporting Language Marcos Rebelo oleber@gmail.com

4. There's More Than One Way to Do It

6. Supports both procedural and OO programming.

7. It has powerful built-in support for text processing

8. It has one of the world's most impressive collections of third-party modules (http://www.cpan.org).

10. Open Source, and free licencing

11. Excellent text handling and regular expressions

12. Large experienced active user base

13. Fast, for an interpreted language

14. Code developed is generally cross plaform

15. Very easy to write powerful programs in a few lines of code

17. Can look complicated, initially, particularly if you're not familiar with regular expressions

19. System administration

20. Most command line applications

21. Batch processing

22. Reports

23. Database access and manipulation

24. Any application involving significant text processing

27. You can use parentheses for subroutines arguments or omit them according to your personal taste. say "Hello, world!";

28. Comments start with a # and run to the end of the line. # This is a comment

30. However, only double quotes interpolate variables and special characters such as newlines ( ): print("Hello, $name! "); # interpolate $name print('Hello, $name! '); # prints $name! literally

32. ... except inside quoted strings: print("Hello world"); # this would print with a # line break in the middle.

35. Alternatively, put this shebang in your script : #!/usr/bin/perl and run your executable script #> progname.pl

36. -e : allows you to define the Perl code in the command line to be executed, -E to get 5.10 #> perl -e 'print("Hello, World! ")'

38. Arrays my @ animals = ('camel', 'lama'); my @ numbers = (23, 42, 69); my @ mixed = ('camel', 42, 1.23);

39. Associative Array / Hash Tables my % fruit_color = ( apple => 'red', banana => 'yellow' );

41. my $ answer = 42;

44. my @ numbers = (23, 42, 69);

46. print( $ numbers [-1] ); # prints 69

48. @ numbers [0..2] ; # gives (23, 42, 69);

50. @ numbers [2, 1] = @ numbers [1, 2] ;

51. ($scalar1, $scalar2) = @numbers;

53. if ( scalar( @animals ) < 5) { ... }

61. my @citiesPT = @{ $cities->{PT} } ;

66. @ARGV : the command line arguments to your script.

67. $ARGV : contains the name of the current file when reading from <> or readline() .

68. @_ : the arguments passed to a subroutine.

69. $a , $b : Special package variables when using sort() .

70. $/ : The input record separator, newline by default.

72. - -= subtraction

73. * *= multiplication

75. || or

76. ! not

78. . string concatenation

79. x string multiplication

80. .. range operator (creates a list of numbers)

81. Most common operators

83. if COND BLOCK else BLOCK

84. if COND BLOCK elsif COND BLOCK

87. This is provided as a 'more readable' version of if ( not( is_valid( $value ) ) ) { ... }

88. 0, '0', '', () and undef are all false in a boolean context. All other values are true.

90. The Perlish post-condition way print("Yow!") if $zippy; print("No cubes") unless $cubes;

92. There's also a negated version (don't use it): until ( is_valid( $value ) ) { … }

93. You can also use while in a post-condition: print("xpto ") while condition;

94. Going throw a hash: while (my ($key,$value) = each (%ENV)){ print "$key=$value "; }

100. next LABEL : starts the next iteration of the loop

103. Warning: last , next , and redo don't work in this case.

104. Exercises 1 - Scalars 1) Implement the ‘Guess the lucky number’. The program shall chose a random number between 0 and 100 and ask the user for a guess. Notice the user if the guess is bigger, smaller or equal to the random number. If the guess is correct the program shall leave otherwise re-ask for a number.

105. Exercises 1 - Array 2) Create an array that contains the names of 5 students of this class. 2a) Print the array. 2b) Create a new Array shifting the elements left by one positions (element 1 goes to 0, …) and setting the first element in the last position. Print the array. 2c) Ask a user to input a number. Print the name with that index.

107. Subroutines

109. all subroutines likewise return to their caller one scalar or a list of scalars.

110. lists or hashes in these lists will collapse, losing their identities - but you may always pass a reference.

111. The subroutine name start with a & , for simplification can be omitted.

113. my $my_max = max( 1, 9, 3, 7 ) ; print $my_max; # prints 9

123. Exercises 2 1) Create a new subroutine that calculates the Fibonacci series. Using this subroutine, do a program that receives multiple numbers as argument and prints the Fibonacci value. F(0) = 0 F(1) = 1 F(n) = F(n-1) + F(n-2) 1a) with presistent variable 1b) with state variable

124. IO

127. open (INFH, " < input.txt") or die $!;

130. open (LOGFH, " >> my.log") or die $!;

134. print OUTFH $record;

135. print { $FH } $logMessage;

138. Slurp: my @lines = <$fh> ; my @lines = readline($fh) ;

140. foreach my $line (<$fh>) { # slurps print "Just read: $line"; }

142. my $txt = do { local (@ARGV, $/) = ($myfile); readline(); };

145. $ARGV has the open file, or '-' if reading STDIN .

147. The __DATA__ token opens the DATA handle in whichever package is in effect at the time, so different modules can each have their own DATA filehandle, since they (presumably) have different package names.

149. --line : printing the line number before the line.

153. Regular Expressions

158. The $ means match at the end of the string or before a newline at the end of the string. print 'Ends with World!' if /World!$/;

160. / [yY][eE][sS] / - match 'yes' case-insensitively.

162. / [0-9a-f] / i - matches a hexadecimal digit

164. / [^0-9] / - matches a non-numeric character

165. / [a^] at/ - matches 'aat' or '^at'; here '^' is ordinary

167. $x = 'bcr'; / [$x] at/ - matches ‘bat’, ‘cat’, or ‘rat’ / [$x] at/ - matches ‘$at’ or ‘xat’ and not ‘bat’, … / [x] at/ - matches ‘at’, ‘bat’, ‘cat’, or ‘rat’

169. D is a non-digit character [^d]

170. s is a whitespace character [ f]

171. S is non-whitespace character [^s]

172. w is a word character [0-9a-zA-Z_]

173. W is a non-word character [^w]

174. The period '.' matches any character but [^ ]

176. /[ ds ]/ - matches any digit or whitespace character

177. / .. rt/ - matches any two chars, followed by 'rt'

178. /end . / - matches 'end.'

179. /end [.] / - same thing, matches 'end.‘

181. Create a Regular Expression that match a 5 digit integer in octal format.

182. Create a program that receives one regexp as the first parameter and a file list and prints the lines matching the regexp.

184. + - one or more

185. ? - zero or one

186. {3} - matches exactly 3

187. {3,6} - matches between 3 and 6

188. {3,} - matches 3 or more

192. At a given character position, the first alternative that allows the regex match to succeed will be the one that matches. 'cats' =~ /c | ca | cat | cats/; # matches 'c' 'cats' =~ /cats | cat | ca | c/; # matches 'cats'

194. / ( ^a|b ) c/ - matches 'ac' at start of string or 'bc' anywhere.

195. /house ( cat| ) / - matches either 'housecat' or 'house'.

196. /house ( cat ( s| ) | ) / - matches either 'housecats' or 'housecat' or 'house'.

200. %+ is ('NAME' => 'Michael')

201. %- is ('NAME' => ['Michael','Jackson'])

202. $1 is 'Michael'

203. $2 is 'Jackson'

208. $& - The string matched.

210. Switch use qw(switch say); given ($foo) { when (undef) {say '$foo is undefined'} when ('foo') {say '$foo is the str "foo"'} when (/Milan/) {say '$foo matches /Milan/'} when ([1,3,5,7,9]) { say '$foo is an odd digit'; continue ; # Fall through } when ($_ < 100) {say '$foo less than 100'} when (&check) {say 'check($foo) is true'} default {die 'what shall I do with $foo?'} }

212. when($foo) is equivalent to when($_ ~~ $foo)

213. Smart Matching $a $b Matching Code Code Code $a == $b # not empty prototype if any Any Code $b->($a) # not empty prototype if any Hash Hash [sort keys %$a]~~[sort keys %$b] Hash Array grep {exists $a->{$_}} @$b Hash Regex grep /$b/, keys %$a Hash Any exists $a->{$b} Array Array arrays are identical, value by value Array Regex grep /$b/, @$a Array Num grep $_ == $b, @$a Array Any grep $_ eq $b, @$a Any undef !defined $a Any Regex $a =~ /$b/ Code() Code() $a->() eq $b->() Any Code() $b->() # ignoring $a Num numish $a == $b Any Str $a eq $b Any Num $a == $b Any Any $a eq $b

215. Create a program that printout all the lines in a file substituting the numbers by #.

218. RegExp /((.*))/ and /((.*?))/ /d{4,}/ /(ww)-(ww)-(ww)/ /W+/

219. Core subroutines

221. length(EXPR) - Returns the length in characters of the value of EXPR.

222. sprintf(FORMAT, LIST) - Returns a string formatted by the usual printf conventions of C.

223. abs(EXPR), cos(EXPR), int(EXPR), log(EXPR), sin(EXPR), sqrt(EXPR) - normal numeric subroutines.

230. Note: If EXPR is omitted, uses $_ .

232. shift(ARRAY), unshift(ARRAY, LIST) - Pops/Pushes a value from/to the start of the ARRAY .

233. Note: in the pop and shift if ARRAY is omitted, pops the @ARGV array in the main program, and the @_ array in subroutines. Avoid to use it.

242. Providing a closure, the elements come in $a and $b . sort {$a <=> $b} (10,9,20) # 9, 10, 20

246. my %a = ('a' => 1); exists ($a{'a'}) # true exists ($a{'b'}) # false

250. eval BLOCK : evaluates the expression and catch's the exception.

251. die EXPR : if out of eval prints the error and exits with the value of $!, otherwise sets the value in $@ and exits eval with undef.

252. eval { $answer = $a / $b; }; warn $@ if $@;

254. Create a subroutine that receives an array of scalars and return a new one just with the strings with length smaller than 20.

256. The remaining in lower-case.

257. Modules and OO

266. our $VERSION = 05.22; Sets the version number. Importing like: use Some::Module 6.15;

268. our @EXPORT_OK = qw($var2 &func2); Lists of symbols that are going to be exported by request (better practice).

269. our ( $var1, $var2 ) = ( 1, 2 ); sub func1() {print("func1 ");} sub func2() {print("func2 ");} Definition of the symbols.

271. The package name pass as the first parameter of the subroutine. Some::Module->func(); $name->func();

272. This will not pass the module name inside the subroutine Some::Module::func(); &{"${name}::func"}();

274. A class is simply a package that happens to provide methods to deal with object references.

275. A method is simply a subroutine that expects an object reference (or a package name, for class methods) as the first argument.

280. package Bat; use base qw(Animal); sub fly { return 1; }

284. Create a set of classes to represent the animal fly capabilities. Shall have two methods fly and name(get/put), the constructor receives the animal name. Consider the following rules: dog is a animal animal doesn’t fly bird is a animal bird flies penguin is a bird penguin doesn’t fly

285. Create a program to test them.

286. Standard Modules

288. warnings - Control optional warnings

289. lib - Manipulate @INC at compile time

290. base - Establish an ISA relationship with base class

291. constant - Declare constants (consider Readonly)

292. subs - Predeclare sub names

295. Carp - better die() and warn()

296. Cwd - pathname of current working directory

297. Exporter - Implements default import method for modules

298. POSIX

299. IPC::Open3 - open a process for reading, writing, and error handling

300. Time::HiRes - High resolution alarm, sleep, gettimeofday, interval timers

302. LWP::UserAgent - Web user agent class

303. HTTP::Request - HTTP style request message

304. HTTP::Response - HTTP style response message

305. LWP::Simple - Simple procedural interface to LWP

306. LWP::Simple::Post - Single-method POST requests

307. HTTP::Async - process multiple HTTP requests in parallel without blocking.

309. Net::SLP - accessing the Service Location Protocol

310. Net::POP3 - Post Office Protocol 3 Client

311. Net::SMTP - Simple Mail Transfer Protocol Client

312. MIME::Lite - low-calorie MIME generator

313. JSON - JSON encoder/decoder

314. JSON::XS – fast JSON serialising/deserialising

316. Apache2::RequestIO - Perl API for Apache request record IO

317. Apache2::RequestRec - Perl API for Apache request record accessors

318. Apache2::RequestUtil - Perl API for Apache request record utils

319. CGI - Handle Common Gateway Interface requests and responses

321. MIME::Base64 - Encoding and decoding of base64 strings

322. Digest::SHA - Perl extension for SHA-1/224/256/384/512

323. Digest::MD5 - Perl interface to the MD5 Algorithm

324. Crypt::DES - Perl DES encryption module

325. Net::SSH - Perl extension for secure shell

327. Test::More - yet another framework for writing test scripts

328. Test::Exception - Test exception based code

329. Test::Output - Utilities to test STDOUT and STDERR messages.

331. DBD::* - Perl DBI Database Driver DBD::SQLite, DBD::CSV, DBD::Google, ...

332. Template – Template toolkit

333. HTML::Template - Perl module to use HTML Templates

334. Advanced Perl

338. Q/A

Perl Introduction

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