PERL.ppt

PERL
(PRACTICAL REPORT AND EXTRACTION
LANGUAGE)
Session-1

INTRODUCTION
What is PERL?
* Practical extraction and report language.
* It is an interpreted language, optimized
for scanning arbitrary text files, extracting
information from them, and printing reports
based on that information.
* Very powerful string handling features.
* Available on all platforms.

ADVANTAGES
*Speed:-As it is an interpretive
language;no need of compiler.Only we
enter the program in the text file and just
run it.
*The regular expressions of Perl are
extremely powerful.
*Uses sophisticated pattern matching
techniques to scan large amounts of data
very quickly.

*Portability:-Perl is a standard
language and is available on all
platforms.
-Free versions are available
on the internet.
*Editing Perl programs:-No
sophiticated editing tool is needed.
-Any simple text editor
like notepad or vi will do.

*Flexibility:-Perl does not limit
the size of your data.
-If memory is available
,Perl can handle the whole file as
a single string.
-Allows one to write
simple programs to perform
complex tasks.

How to run Perl?
*Perl can be downloaded from the internet.
*Available on almost all platforms.
Assumptions:-
*For windows operating system,we can run Perl
program from command prompt.
-Rum "cmd" to get command prompt window.
*For Unix/Linux,we can run directly from the shell
prompt.

EXAMPLE
*For Windows
-Create a directory/folder where you will be
storing the Perl files.
-Using any text editor create a file "first.pl"
with the following content:
print "Good morning Indian";
print "This is my first Perl programn";
-Execute the program by typing the
following at the command prompt:
perl first.pl

*On Unix/Linux,an additional line has to be
given at the beginning of every Perl
program.
#!/usr/bin/perl
print "Good dayn";
print "This is my first Perl programn";

Variables
*Scalar variables
-A scalar variable holds a single value.
-Other variable types are also available which
are
(a)Array
(b)Associative array
-A '$'is used before the name of a variable to
indicate that it is a scalar variable
$x=100;

*Some examples:
$x=100;
$name="Suman Ghosh";
$average=56.98;
* Variables do not have any fixed types.
*Variables can be printed as:
print"MY name is $name,the average marks
obtained is $averagen";

* Data types:
*Perl does not specify the types of
variables.
-It is a loosly typed language.
-Languages like C or java are strongly
typed.

*An example:
$stud="Rahul";
$marks=86;
print"Marks obtained by $stud is $marksn";
print'Marks obtained by $stud is $marksn';

*The program will give the following
output:
Marks obtained by Rahul is 89
Marks obtained by $stud is $marksn
*What do we saw:-
-If we need to do variable interpolation,use
double quotes;otherwise ,use single quotes.

*Another example:
$expense='$10';
print"The expenditure is $expensen";
The output is
The expenditure is $10
If $10 is within double-quotes than the
perl interpreter may get confused any
will try to find the value of variable
100.

Expressions with Scalars
*Illustrated through examples(syntax similar to C)
$a=89;
$a++;
$b=100;
$total;
$a=$b**10; #exponentiation
$a=b%10; #modulus
$balance=$balance+Sdeposit;
$balance +=balance;

*Program in Unix/Linux
#!/usr/bin/perl
$a=89;
print "the value of a is $an";
$a++;
print "the incremented value of a is $an";
$b=100;
print "the value of b is $bn";
$total=$a+$b;
print"the total value is $totaln";
$a=$b**2; #exponentiation
print "the value of a is $an";
$b=a%10; #modulus
print "the value of b is $bn";

*Output of above program is:
the value of a is 89
the incremented value of a is 90
the value of b is 100
the total value is 190
the value of a is 1e+20
the value of b is 0

*Operations on strings:
-Concatenation :the dot (.) is used.
$a="Good";
$b="day";
$c="n";
$total=$a.$b.$c; #Concatenate the
strings
$a .="nightn"; #add to the string $a

*Example
!/usr/bin/perl
$a="Welcome to";
$b=" ASILICON DESIGN";
$c="n";
$total=$a.$b.$c; #Concatenate the
strings
print" total is $totaln";
$a .=" Asilicon familyn"; #add to the
string $a
print"the value of a is $a";

Output of above program is:
total is Welcome to ASILICON DESIGN
the value of a is Welcome to Asilicon family

*Arithmetic operation on strings
$a="bat";
$b=$a+1;
print$a." and ".$b;
will print bat and cat
*Operations carried out based on ASCII codes.
-May not be always meaningful.

*String repetation operator(x).
$a=Sbx4;
will concatenate four copies of $b and
assign to $a.
print "Ba"."na"x2;
will print the string "banana".

*Example
#!/usr/bin/perl
$a="anocon";
$b="da";
$y=$a.$b;
print "$yn";

String as a Number
*A string can be used in a arithmetic expression.
-How is the value evaluated?
-When converting a string to a number,Perl takes
any spaces,an optional minus sign,and as many
digits it can find with (with dot) at the begining of
the string,and ignores everything else.
Examples
"89.98" evaluates to 89.98
"4757java789" evaluates to 4757
"apple" evaluates to 0

Examples:-
#!/usr/bin/perl
$a=90;
$b="apes";
$c=$a+$b;
print"the value of c is $cn";
$d="100hyhy89";
$e=$a+$d;
print"the value of e is $en";;

Output of above program is:
the value of a is 90
the value of e is 190

Escaping
*The chracter '' is used as escape chracter.
-It escapes all of perl's special characters(e.g
$,@,#,etc).
Example
#!/usr/bin/perl
$a=100;
print "the value of $a is $an";
Output of above program is
the value of $a is 100

Line Oriented Quoting
*Perl supports specification of a
string spanning multiple lines.
-Use the marker "<<".
-Follow it by a string,which is
used to terminate the quoted
material.

Example 1
#!/usr/bin/perl
print<<terminator;
Hello, John how are you?
Bye,have a nice day.
terminator
Hello, John how are you?
Bye,have a nice day.

Example2
#!/usr/bin/perl
print<<john;
Welcome home.
How are you.
john
Welcome home.
How are you.

Basic difference between List and Array
*List is an ordered list of scalars.
*Array is a variable that holds a list.
*Each element of an array is a scalar.
*The size of an array:
-Lower limit:0
-Upper limit:No specific limit ;depends on the
virtual memory.

List literals
*Examples:
(10,20,67,190,187)
('red',"blue","green")
("a",1,9,7,'h')
($a,89)
() #empty list
(80..90) #list constructor function
('A'..'Z') #same,for letters

Specifying Array Variable
*we use the special character '@'.
@day #denotes an array
@x #denotes an array
The individual elements of the array are
scalars,and can be referred to as:
@day[0] #first element of @day
@day[1] #second element of @day

Initializing an Array
*Two ways:
-specify values,separated by commas.
@color=('red','green','blue','black');
-Use the quote words(qw) function ,that
uses space as the delimiter:
@color=qw(red green blue black);

Example-1
#!usr/bin/perl
$a=8;
$b=7;
$c=98;
$d=45;
@num=($a,$b,$c,$d);
print"the value of num array is @numn";;
Output of above example is
the value of num array is 8 7 98 45

Example 2
#!/usr/bin/perl
@color=qw(red green yellow black);
print "the value of first element is @color[0]n";
print "the value of second element is @color[1]n";
print "the value of third element is @color[2]n";
print "the value of fourth element is @color[3]n";
print"the value of color array is @colorn";

the value of first element is red
the value of second element is green
the value of third element is yellow
the value of fourth element is black
the value of color array is red green yellow black

PERL.ppt

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