Introduction to perl_ a scripting language

Practical Extraction and Report Language
‘A general-purpose programming language originally developed for text
manipulation and now used for a wide range of tasks including system
administration, web development-CGI scripting, network programming, GUI
development, and more.’
‘The language is intended to be PRACTICAL (easy to use, efficient, complete) rather than
BEAUTIFUL (tiny, elegant, minimal).’
And Some More:
‘Many earlier computer languages, such as Fortran and C, were designed to make
efficient use of expensive
computer hardware. In contrast, Perl is designed to make efficient use of
expensive computer programmers.
Perl has many features that ease the programmer's task at the expense of greater
CPU and memory requirements.
These include automatic memory management; dynamic typing; strings, lists, and
hashes; regular expressions;

 Larry Wall invented PERL in the mid-1980's
Larry Wall was trained as a linguist, and the design of Perl is very much
informed by linguistic principles.
Examples include Huffman coding (common constructions should be
short), good end-weighting (the important information should
come first), and a large collection of language primitives. Perl favors
language constructs that are natural for humans to
read and write, even where they complicate the Perl interpreter.’
Perl has rapidly become the language of choice for writing programs
quickly and robustly across a wide range of fields - ranging from
systems administration, text processing, linguistic analysis, molecular
biology and (most importantly of all) the creation of dynamic World
Wide Web pages. It has been estimated that about 80% of dynamic
webpages worldwide are being created by Perl programs.

 PERL encompasses both the syntactical rules of the
language and the general ways in which programs are
organized
 It is dynamically typed language.
 Relatively easy to learn (and easier to make a mess
too).
 incredibly flexible coding style (some argues it is too
flexible).
 Perl is interpreted not complied hence its scripting
language.
 It follows OOPs concepts.
 http://perldoc.perl.org/perldoc.html

 CPAN(comprehensive Pern Archive
Network) : consists of Additional perl
modules(more than 100,000 modules),
documentation,various releases etc.,
 HTTP://cpan.org/

 Define the problem
 Search for existing code
 Plan your solution
 Write the code
 Modify ->Debug ->Modify
 Run the code

 Now-a-days On *nix
OSes Perl comes
installed
automatically. And
can be located at
/usr/bin/perl and /
usr/local/bin/perl
To install Perl on
Windows :
 http://strawberry
perl.com/
 http://www.activ
estate.com/active
perl

 Open a terminal
 Make a perl dir(directory) in your home dir
 Move into the perl directory
 Create a file named ‘hello_world.pl’
 Open the file in your text editor
 Code the program
 Save the file
 Make the program executable
 Test the program.

 # Unix
 perl -e 'print "Hello worldn"‘
 # MS-DOS
 perl -e "print "Hello worldn""

Location of perl is normally in
/usr/bin/perl and /usr/local/bin/perl
Perfix the script with #!/usr/bin/perl
And also you can type in “use <version>” to use the
latest version
#!/usr/bin/perl -w
use strict;
use warnings;
my $message = ‘Welcome to perl tutorial’;
print “t hello world $message.!!n”;
print ‘hello world $message.!!n’
#prints $messagen literally

 Scalar: a single piece of information. Scalars can
hold numbers or text
 $ is the identifier of scalar in perl
 There are special variables for the system: $ARGV,$!
 @scores = (32, 45, 16, 5);
 @cars = (BMW,Renault,Jaguar,Ferrari); or @cars =
qw(BMW Renault Jaguar Ferrari);
 my @sorted = sort @cars;
 my @backwards = reverse @scores;
 $multilined_string = <<EOF; This is my multilined string note that I am
terminating it with the word "EOF". EOF
 Scalar values are represented as $var = <num/char> ; Dynamic typing

 Array/List: an ordered collection of scalars
 my @array = ( 1, 2 );
 my @words = ( "first", "second", "third" );
 my @mixed = ("camel", 42, 1.23);
print $mixed[$#mixed]; # last element, prints out
1.23
 Subscripts
An array can be accessed one scalar at a time by specifying a
dollar sign ($ ), then the name of the array (without the
leading @ ), then the subscript inside square brackets.
 For example:
@myarray = (5, 50, 500, 5000);
print "The Third Element is", $myarray[2], "n";

Declaration of HASHes
%scientists =
(
"Newton" => "Isaac",
"Einstein" => "Albert",
"Darwin" => "Charles",
"Feynman" => "Richard",
);
print "Darwin's First Name is ", $scientists{"Darwin"}, "n";
Hash subscripts are similar, only instead of square brackets curly brackets
are used

my %fruit_color = ("apple", "red", "banana", "yellow");
 To get at hash elements:
$fruit_color{"apple"}; # gives "red“
 To get a lists of keys and values with keys() and values().
my @fruits = keys %fruit_colors;
my @colors = values %fruit_colors;

 Some scalar variables have special meaning
in Perl. Of note are `$_`,
`$!`, `$0`, and `$$`.

 There are system defined functions for
operations on Scalar variables, Arrays,
Hashes, File Handlers, Regular Expressions,
Sub routines, Modules etc., which appear like
keywords some times and take arguments
Eg: Chomp, join, my, our, grep, mkdir, open,
import,defined,undef,sort,reverse etc.,
For detailed description follow: http://perldoc.perl.org/perlfunc.html#Perl-Functions-by-Category

 double quotes(“), single quotes(‘) and
multi-line quoting(qq) :
$var =10;
$text = “There are $var apples”
$text2 = ‘There are $var apples’
$text3 = qq{
There
are
$var
apples};

Functions are blocks of code which perform specific task
#takes no input and returns no output… common practice to use
#‘main’ as the starting point in a script.
sub main {
…
}
#Takes 2 *scalars* as input sums them and returns one scalar.
sub sum_2_numbers {
my ($numA,$numB) = @_; #get passed in values
my $sum = $numA+$numB; #sum numbers
return($sum); #return sum
}

 if/else
 if ( condition ) {…} elsif ( other condition ) {…} else {…}
 Unless
die "Can't cd to spool: $!n" unless chdir '/usr/spool/news';
 While
while (($key, $value) = each %hash) {
print $key, "n";
delete $hash{$key};
}
 Until
$count = 10; until ($count == 0) { print "$count "; $count--;}
 foreach
foreach $index (0 .. $#ARRAY) {
delete $ARRAY[$index];

 Logical operators: ==, !=, &&, ||, eq and ne

 Undefined/” ”/0 values are treated as
false
 Scalars are evaluated as:
numbers are evaluated as true if non-zero
strings are evaluated as true if non-empty
$var = “false”;
if($var)
{
say “$var is true!”;
}

 Scripts can take inputs in two ways:
 Arguments
 ./print_args.pl ARG1 ARG2
 Prompted inputs from users
 $user_text = <STDIN>

 Things don’t always come out as expected. It
is good to check the output of important
functions for errors, it is highly
recommended to validate any input from
users or external sources
 Die
 Warn

Introduction to perl_ a scripting language

Introduction to perl_ a scripting language

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