Perl Basic Kit

Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall, a linguist working as a systems administrator for NASA, in 1987, as a general purpose Unix scripting language for report processing. Perl borrows features from other programming languages including C, shell scripting (sh), AWK, sed and Lisp. The language provides powerful text processing facilities without the arbitrary data length limits of many contemporary Unix tools, facilitating easy manipulation of text files.

Version history

5.8.8, 5.10 Not newest but most used version and quite updated (use strict…)

6 Will supose a new era of Perl making it less cryptic.

Installation:

1. Download lastes Perl release.
2. sh Configure -de -Dprefix=/home/user/perl-version
3. make
4. make test (optional)
5. make install

Install desired modules: cpan -i Module::Name (ie cpan -i XML::Parser, and follow all instructions) (See the specific section of this page)

Example:

#!/usr/bin/perl (better to use -w switch)
print "Hello, world!\n";

Use #!/usr/bin/perl -w to show and handle warnings (better error localization, recomended)

Use use strict to make perl more restrictive in defining local and global variables.
If you planed to use utf8 chars be careful, even if your ecoding is utf8 you may consider: use utf8 and use utf8;
use encoding 'utf8'; commands.

---> VER PDF BUENISIMO DE USAR UNICODE (UTF-8 EN PERL). En Dropbox/Programing/Perl
IMPORTANTISSIM: http://perldoc.perl.org/perlunicode.html

Lowercase utf8 chars ÀÑ -> àñ with lc() if the encoding is well defined.

Advantages: Good performance, powerful regexps and text I/O handling, short code.
Disadvantages: Difficult to learn, cryptic to read.

Regular expressions

regular expressions are mostly like sed.

// match
s//// replace

But the best way to make it is with curly braces {}
m{} match
s{}{}

POSIX

[[:alpha:]] \w
[[:digit:]] \d
[[:alnum:]]
[[:punct:]]
[[:blank:]] \t
[[:space:]] \s

options:

    m  Multiline mode - ^ and $ match internal lines
    s  match as a Single line - . matches \n
    i  case-Insensitive
    x  eXtended legibility - free whitespace and comments
    p  Preserve a copy of the matched string -
       ${^PREMATCH}, ${^MATCH}, ${^POSTMATCH} will be defined.
    o  compile pattern Once
    g  Global - all occurrences
    c  don't reset pos on failed matches when using /g

i ignore case
g global (more than one occurrence)
o complile only once regular expressions with variables (improves performance)
s ingludes \n as a character for . operator.
m multiline matches
x allow to make a long regular exression ignoring blancs and newlines. Example:

    s{
       <a \s+ href="([^"]+)">
        (.*?)
       </a>
     }
     {link=$1, text=$2}xms;

Backreference on match using    \groupnumber
Backreference on replace using  $groupnumber
Example:
s/(\d\d?([\.\/-])\d\d?\2\d\d(\d\d)?)/<TIMEX3 type=\"DATE\">$1<\/TIMEX3>/g

Always make use of non-capturing groups when capturing is not needed: (?:...)

REview:

http://perldoc.perl.org/perlreref.html

http://www.regular-expressions.info/

Perl Basics

Useful perl cheat sheet. (perldoc perlcheat)
my: local variables. If you already included use  strict at the top of your program,
perl will check that all variables are  introduced with my. Variables made private
with my only exist within a block (curly  braces). The subroutine body is a block,
so the my variables only exist  within the body of the subroutine.

sub: subroutine (function)

A variable is defined by the ($) symbol (scalar), the (@) symbol (arrays),
or the (%) symbol (hashes). Note that in perl arrays and lists are the same thing, and hashes are associative arrays.
$somenumber = 4;
$myname = "some string";
@array = ("value00","value01","value02");

%hash = ("Quarter", 25, "Dime", 10, "Nickle", 5);

To use global variables in "use strict" you have to redeclare them in each function by:

 use vars qw($scalar %hash @array)
while(<>) # read input

The <> symbol will return false only once.  If you call it
again after this, it will assume you are processing another @ARGV
list, and if you haven't set @ARGV, it will input from STDIN.
Execute external Commands (system)

There are many ways to execute external commands from Perl. The most commons are:

• system function
• exec function
• backticks (“) operator. $output=`ls -la` (like bash scripts)
• open function (most powerful, you can capture even STDERR)

All of these methods have different behaviour, so you should choose which one to use depending of your particular need. In brief, these are the recommendations:

XML and PERL (GOOD COMBINATION)

http://perl-xml.sourceforge.net/faq/

www.xml.com (perl)

SPECIAL VARIABLES

$_    default variable
$0    program name
$/    input separator
$\    output separator
$|    autoflush
$!    sys/libcall error
$@    eval error
$$    process ID
$.    line number
@ARGV command line args
@INC  include paths
@_    subroutine args
%ENV  environment

Perl Data Structures (@arrays #hashes)

See Perl Data Structures CookBook (pdf)

@array=(a, b, c);

$#array –> 3

$array[1] –> b

shift

pop/push

splice

references and values… arrays of arrays

print “\t[ @{$array[$n]} ]\n”;

note: the outer [] in the print are important.

Control Sequences

while

for

last –> break

next –> continue

redo –> ??? volver a empezar despues de un splice…

Install MODULES from CPAN

1. Install all dependent packages for CPAN
sudo  apt-get install build-essential

2. invoke the cpan command as a normal user

$cpan

But once you hit on enter for “cpan” to execute, you
be asked of some few questions. To make it simple for
yourself, answer “no” for the first question so that
the latter ones will be done for you automatically.

3. Once the above is done, you will be present with the cpan
prompt. now enter the commands below

make install

install Bundle::CPAN

4. Now all is set and you can install any perl module you want. examples of what installed below

cpan prompt>  install  IO::File
cpan prompt>  install  Net::SMTP_auth
cpan prompt>  Email::MIME::Attachment::Stripper
cpan prompt>  Mail::POP3Client