Outline. Introduction to Perl. Why use scripting languages? What is expressiveness. Why use Java over C

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1 Outline Introduction to Perl Grégory Mounié Scripting Languages Perl jeu. Basics Advanced 1 / 30 2 / 30 Why use scripting languages? What is expressiveness Why use Java over C Memory management Portability Huge standard library Why use Perl over Java No compilation, just interpretation: easy deployment No static typing Expressiveness with high level operators Expressiveness Expressiveness is target dependent and user expertise dependent. The goal is to build complex program with a small number of line of code. Common use cases of scripting language: text manipulation, filtering, prototyping, complex program, graphical/command-line interface. 3 / 30 4 / 30

2 Sh/Bash Python process management oriented easy to start and control processes and interconnect their I/O cryptic syntax for everything else All variable name start with a $ (idem in Perl) Python was designed to be easier to learn than Perl. Remove the useless characters use indentation as block (be careful with copy-paste! use automatic indentation) object oriented from the start: all functions reference are stored in a programmable dictionary (overloading at runtime) Few strange operators Easy to understand. If you can read Java code, you will understand Python code. drawback: increase verbosity 5 / 30 6 / 30 Ruby History More expressive than Python regexp/string operators as in perl a block has arguments (awesome and useful!) [1, 3, 5, 7, 9].find { v v*v > 30 } More readable than Perl Writing code using explicit Javadoc-like convention no strange character ($, %, ) in the code anymore (save for blocks) Perl was written by Larry Wall in It was designed for text manipulation, borrowing syntax from C, awk, sed, grep, cut, expr, and sh. Mantra of Tim Toady (TIMTOWTDI) There Is More Than One Way To Do It 7 / 30 8 / 30

3 Documentation Books Perldoc Perl has an extensive an high quality documentation. You should learn to use it. perldoc perltoc perldoc perlintro perldoc perlop perldoc perlfunc There exists numerous books on Perl and web tutorial. Modern Perl CC-BY-NC edited book highlighting that Perl is a language Programming Perl By Larry Wall et Al. Publisher: O Reilly. The best SECOND book to read on perl :-) 9 / / 30 Perl is a contextual language Perl is a contextual language II Theorem (Plural) void, scalar, list contexts fibonacci(10); # void context, valid to not compute my $single_value = fibonacci(10); # scalar context, the value = fibonacci(10); # array context, all the fibo values from 1 to 10 Theorem (Gender) boolean, numeric, string contexts my $toto = "1" + "1"; # numeric context: 2 my $titi = 1. 1; # string context: "11" my $tata =!1; # boolean context: false "titi" == "tata"; # numerical equal: true "titi" eq "tata"; # string equal: false 11 / / 30

4 Perl is a contextual language III Perl operator and library extensively use a global implicit variable Theorem (It) use Modern::Perl; while (<LINE>) {# read line a line chomp; # remove "\n" from it say scalar reverse; # print the reversed integer } It may kill you if you sleep [cf Stephen King] Use local variable ( when using $_; Theorem (Implicit array) Perl is a contextual # outside function Theorem (Not implemented)...; # the dot operator trigger an exception Not implemented if executed. while(my $_ = <STDIN>) {... while(my $line = <STDIN>) { / / 30 Scalars Quoted String Several string quotations with subtle differences The standard variable Scalar $toto= 1; $tata= 1.5; $titi= "2"; $tutu= \@toto; # ref to toto array my $chaine="ls"; print titi $chaine q{toto $chaine}; # titi $chaine print "titi $chaine" qq/toto $chaine/; # titi ls print $chaine qx!$chaine!; # list directory print qw(a b c); # array of 3 string, useful with "use" print <<EOF; # verbatim inside, EOF for single quote semantic blab bla bla bla EOF print << COMMAND ; # string build with a multiline command date uname -a COMMAND 15 / / 30

5 Loop and test Arrays Exercice: 1 to 10 print values from 0 to 9, on the same line the C way with the operator with local variable and with implicit variable = ( "toto", "titi", 1, "a" ); print $array[0]; # print toto print $#array; # index of last, print 3 print $array[0..1]; # array slice = = map { print # apply the block to all element 17 / / 30 Operators change the context Array and string relation + - * / ==!= > < <=>; # numeric operators eq ne le ge gt lt cmp ~~; # are string operator Exercice: Add values Add the first two arguments of your script and print the result value Add all the arguments of your script and print the result value Concatenate all the arguments and print the result string Split = split(";", "a;b;c;d;e;f"); Join my $chaine = 19 / / 30

6 Hashes Regular Expressions Theorem (Matching, Substitute, Transliteration) Creation my %mark= ( "Eve", 17, "Bob", 12, "Alice", 16); my %mark= ( Eve => 17, Bob => 12, Alice => 16 ); my $mark_ref = { Eve => 17, Bob => 12, Alice => 16;} print $mark{"eve"}."\n"; $mark{bob}= 2; $mark_ref->{bob}=3; = keys %mark; = values %mark; m/regular expression/; #matching s/regexp/regexp/modifiers; #substitution tr/regexp/regexp/; #transliteration Perl allows to test and modify string. They are often use with operators to select the string. my $sentence= "Hi Guys!\n"; if ($sentence =~ m/guys/) { $sentence =~ s/guys/girls/; } print $sentence; 21 / / 30 Regular Expression Input/Output Exercice starting with the string hi guys! parse a string to change all h by H if it contains Hi if it does not contain the word little, insert it between Hi and Guys print the result File handle allow integrated manipulation open(myfile, "toto.txt", "<"); while(my $line= <MYFILE>) { print $line; break; # just read one line } <MYFILE> close MYFILE; 23 / / 30

7 Subroutine Exercice: user You may define subroutine (function) Almost no parameter management sub fibo { my $n = shift; return 1 if $n < 2; return fibo($n - 1) + fibo($n - 2); } print fibo(10); Human user of the computer File /etc/passwd A human needs a /home User using firefox File/Pipe Process list with ps aux split/splice for column parsing One user, One name (hash) Get the first three images of xkcd to get the text of the URL of the 5th image File/Pipe rename file to include the number 25 / / 30 References Complex Data Structures No pointer, just references. 27 / / 30

8 Package Object Perl ICS examples 29 / / 30