Archive for May 2013
PERL-Language
PERL
(PRACTICAL EXTRACTION AND REPORT LANGUAGE)
1.INTRODUCTION:-
1.1 Internet programming languages: -
Internet programming was given
a boost with the advent of WWW to satisfy the demand for Internet based
applications, which grew manifold. This application requires a language for
their development. These languages were required to provide dynamic and an
interactive content to static web pages. The client /server model was the
obvious choice for Internet applications.
In client server model the
client sends request to the server, the server doesn’t have the capability to
process the client requests. So, it internally contacts CGI to process the
client request. The CGI process the client request and sends the response back
to server. Now, the server sends the response to the client in the form of HTML
page.
2.CGI (COMMON GATEWAY INTERFACE): -
The common gateway Interface (C.G.I) is a
specification defined by the World Wide Web consortium, defining how a program
interacts with a Hyper Text Transfer Protocol (HTTP) server. The CGI provides
middleware between www servers and external databases and information sources.
2.1 WHY IS CGI USED: -
The interactive web pages, that displays some
present information. These interactive web pages enable a client to send
information to the web server and get back a response that depends on the
input.
To create an interactive web page,
HTML elements are used to display a form that accepts a client's input and
passes this to special computer programs on the web server. These computer
programs process a client's input and return requested information. These
programs are known as gateways because they typically act as a conduit between
the web server and an external source of information such as database.
2.2 COMMON USES OF CGI: -
==>Gathering
user feedback about a product line through an
HTML form.
==>Querying
an oracle database and rendering the result as an
HTML SSdocument.
2.3 PROCESS OF CGI: -
==>A client makes an HTTP request
by means of a URL. This URL could be typed into the 'location' window of a
browser.
==>From the URL, the web server
determines that it should active the gateway program listed in the URL.
==>The gateway program processes
the information and returns HTML text to the web server. Then it returns HTML
text to web browser.
==>The web browser displays the
document received from the web server.
2.4 HOW INFORMATION IS TRANSFERRED FROM THE WEB BROWSER TO
A CGI PROGRAM: -
The web browser uses the method attribute of the <form> tag to
determine how sends the form's data to the web server. There are two submission
methods: GET and POST.
GET=>>The web browser submits the form's data as a part of a URL. The GET
command sends a URL to the web server. If the form's data is sent to the web
server using the GET command, the browser must include all data in the URL.
POST=>>The web browser sends the form's data separately from the URL as a
stream of bits. In the POST method, the web browser sends the POST command to
the server and includes the form's data in the body of that command. The POST
method can handle any amount of data.
2.5 WHY IS PERLFOR CGI? : -
A CGI program can be written in any language like c, c++, VBscript,
perl, TCL, REXX, python, Icon, Applescript, Unix shell scripting. But PERL is
especially suited for this because perl programs are easy to learn and write.
PERL is a scripting language, which means it does not have to be compiled. Instead,
an interpreter executes the perl script, this makes it easy to write and test
PERL scripts, because they do not have to go through the typical
edit-compile-link cycles.
3. INTRODUCTION TO PERL:-
3.1
HISTORY OF PERL: -
Developed by "Larry Wall"
basically on UNIX systems. The basic reason for developing PERL is it gives
much flexibility in string manipulations. PERL is an acronym for
"Practical Extraction and Reporting Language". It was
originally created to extract information from text files and then use that
information to prepare reports.
Perl has gained recent attention in
the explosion of the W.W.W as a quick and effective way to mock up applications
that provide much of the web's interactivity. It has a lot of syntax that can
make scripts contain more characters from the top row or the keyboard then any
other, but that is not necessary to get anything done. In fact there are few of
the traditional limitations that interpreted language impose.
3.2
FEATURES OF PERL: --
--->PERL is case sensitive
language.
--->PERL is freeform language.
--->Each PERL statement must end
with a semicolon (;).
--->Comments begin with hash mark
(#).
--->A group of PERL statements
can be treated as a block by enclosing them in braces ({…}).
--->It is interpreted based
language.
--->It is a scripting language.
--->String manipulations are very
easy.
--->Code optimization.
3.3 STRATEGY: -
Strategy for this seminar is to establish the basics of perl. The
script we'll be useful to anyone who has wanted to create some interactive
pages on the World Wide Web. Web servers
usually support running auxiliary programs to facilitate interactive content.
There is standard called C.G.I, which defines a minimum set of environment
variables that the program can use to determine its response.
The program we write will take the results
of an HTML form and mail the values to a specified person. Writing the HTML for
this form is beyond the scope of this seminar, but a sample form be provided.
The beauty of this program is that any
user on the web server can use it to response to their forms. You don't need to
give everyone access to your server configuration. Users will enable themselves
for this program, and then can write arbitrary forms from anyone on the web to
fill out.
4.VARIABLES IN PERL:-
Variables are used to store data. In PERL each variable has a name and
can store any type of data. Each variable name in PERL begins with special
character. There are five special characters are used in PERL.
* A
dollar ($) sign
* An at
(@) sign
* A
percent (%) sign
* An
ampersand (&) sign
* A
less than greater than (<>) symbol
Special character denotes the variable
type. There are five types of variables available in PERL language.
* Scalar variables
* Indexed Array variables
* Associative Array variables
* Subroutine
* File handler
In PERL, there is no data type for a variable. The sex or data type of
the variable is dependent on the context in which it is used.
4.1
SCALAR VARIABLES: -
A scalar variable can reference a string value
or a numeric. We can identify these two by visible difference. If the value of
the variable is surrounded in single of double quotes, then PERL treats the
variable as a string. If there are no quotes, then PERL has to decide if the
value is a string or a numeric value. These variables are preceded by the '$'
sign.
$First
name="Sanjay";
$Last name="Kumar";
$Age=23;
4.2
INDEXED ARRAY VARIABLES: -
These arrays are indexed by only
integer values. Indexed arrays are denoted by the '@' sign.
Ex:-@months=("jan","feb","mar","apr","may","jun");
Arrays are start at index 0. In the
above example @months [0] will have a value Jan and @months [1] have Feb.
Extracting
Information from an Indexed Array: -
The 'qw' keyword is a shortened form
used to extract individual words from a string. The most common method of
extracting information from an array is to index the array elements directly.
Ex: -@months=qw (Jan Feb mar apr may
jun);
for($x=0; $x<=$#months; $x++)
{
Print "index [$x]=$months [$x]
\n";
}
4.3
ASSOCIATIVE ARRAY VARIABLES: -
These arrays are also called 'Hash' arrays.
They are indexed by string values instead of by integer index values. These
arrays are identified by '%' sign.
Ex: -%cities=("a","hyderabad","b","bangalore","c","chennai");
The
above example can be rewritten as: -
$Cities {'a'}=Hyderabad;
$Cities {'b'}=Bangalore;
$Cities {'c'}=Chennai;
Extracting
Information from an Associative array:-
The contents of an associative array can be
accessed using three PERL functions. They are: keys, values, each.
‘Keys’ function: -
The keys function returns a list of
the keys of the given associative array.
Ex: -#! g:\perl\bin\perl
%Cities=("a","hyderabad","b","bangalore',"c","chennai");
for $key (keys% cities)
{
Print "key=$key \n";
}
'Values’ function: -
The values function can be used to
directly access the values in an associative array.
Ex: -#! g:\perl\bin\perl
%Cities=("a","hyderabad","b","bangalore");
for $value (values %cities)
{
Print "value=$value \n";
}
'Each’ function: -
The each function returns a
key-values pair from the associative array.
Ex: -#! g:\perl\bin\perl
%Cities=("a","hyderabad","b","bangalore");
While (($key, value)=each% cities)
{
Print "key=$key value=$value
\n";
}
4.4
SUBROUTINE DATA TYPES:-
Subroutines are identified with an
"&" symbol and subroutine name.
Ex:
$i=10;
$j=20;
$Large=&max ($i, $j);
Print $large;
Sub max
{
My $max=shift (@_)
for each $arg (@_)
{
if ($max<$arg)
$Max=$arg;
}
return $max;
}
5. ARITHMATIC&RELATIONAL
OPERATORS:-
=>>Arithmetic operators are same as
in the C language.
=>>In some languages, relational
operators are used to comparing numbers and also for text strings. But, PERL
has a complete set of relational operators for comparing strings.
Operator Example Description
eq $x eq $y value is true if the strings $x
and
$y are equal, else false.
ne $x ne $y value is true if the strings $x and
$y are not equal, else false.
gt $x gt $y value is true if $x is greater
than
$y, else false.
ge $x ge $y value is true if $x is greater
than
Or equal to $y, else false.
lt $x lt $y value is
true if $x is less than $y,
else false.
le $x le $y value is true if $x
is less than or
equal to $y, else
false.
cmp $x cmp $y value is -1 if $x is less than $y, 0
if the strings are equal and 1 if
$x is greater than $y.
6. CONTROL STRUCTURES:-
Only simple programs are
executed strictly in linear order. More complex programs require that
conditions be tested and acted upon appropriately some conditions will require
that a statement or block of statements be executed over and over again a
specified number of times, or until condition is met or satisfied.
The basic control structures in perl
are:
1.if/else
2.nested if/else
3.unless
4.while
5.until
6.do...while
7.do...until
8.for
9.foreach
7. FUNCTIONS IN PERL:-
7.1 String Functions: -
* Chop () - chop cutoff's or removes the last
character in the scalar variable.
Ex: -#! g:\perl\bin\perl
$line="I LIKE YOU";
Chop ($line);
Print “line";
Out put is I LIKE YO.
* Chomp () - Removes the new line character if it
presents in the string.
* Sub string () –Using this to extract some
part of a string.
Syntax: -substr (string, offset, length)
* Length () - It is used to find the
length of the string.
Ex:-$name="I LIKE YOU";
$Length=length ($name);
* Split ()
- Based on the delimiter you can split the array.
Split (/#/, @x)
Now @x=(10,
"svccs", 4, "mca");
7.2 Array Functions: -
* Shift ()
- Removes the first element from the array
Ex: -#! g:\perl\bin\perl
@Cities=qw (H B C);
$delcity=shift (@cities);
Print "@cities";
Output is- ("B","C")
* Unshift ()
- Inserts the element at the first position of the array.
Ex: -#! g:\perl\bin\perl
@Cities=qw (H B C)
Unshift
(@cities,"M","O");
Print "@cities";
Output is-
("M","O","H","B","C")
* Pop ()
- Removes the last element from the array.
Ex: -#! g:\perl\bin\perl
@Cities=qw (H B C);
$delcity=pop (@cities);
Print "@cities";
Output is-
("H","B")
* Push ()
- Inserts the element at the end of the array.
Ex: -#! g:\perl\bin\perl
@Cities=qw (H B C);
Push
(@names,"M","O");
Print "@cities";
Output is- ("H","B","C","M","O")
* Sort ()
- Based on the ASCII value the List will be sorted.
Syntax: -sort (@cities);
* Reverse ()- List will be completely
reversed.
Syntax: -reverse (@cities);
*
Splice () -
Simple and complex function which gives you the
Multiple
functionality against arrays. This function acts differently depending upon the
no. of arguments passed.
By this function we can
perform
*
Delete * Insert *Replace operations.
If the number of arguments in splice
function is 3 then it signifies the Delete operation.
If the number of arguments in splice
function is 4 then it signifies the either Replace or Insert operations.
If the third parameter in the splice
command is '0' then it signifies inserts operation else if the third parameter
is other than '0' then it signifies Replace.
DELETE: -
Splice
(@x, 0,1) ---- Removes the
first value.
Splice
(@x, 1,3) ---- Removes 3
elements starting from
Second
position.
Splice
(@x, $#x/2,2) ---- Removes 2
elements from the middle
Position.
INSERT: -
$P="Hello World";
Splice (@x, 0,0, $p)
Now @=(,"Hello World",
10, "svccs", 4, "mca");
REPLACE: -
$Val=100;
Splice (@x, 2,1, $val)
Now
@=(,"Hello World", 100, "svccs", 4, "mca");
* Concatenation-The string concatenation
operator is represented by a period (".").
Ex: -#! g:\perl\bin\perl
$First
name="Sanjay";
$Last
name="Kumar";
$Full name=$first
name. $Last name;
Print "$full
name";
Output is-sanjaykumar
* Join()
- We can join all the
elements of the array.
Join ("#",
@x)
Now @x=(10#
"SLNCS"# 4# "mca");
8. FILE HANDLERS:-
In each and every language input and
output both from standard devices and from disk files is important.
Perl sends data to output devices and receives data from i/p devices
via I/O channels. The I/O channels are called file handles. File input from the
keyboard and output to the printer, perl provides two file handles they are
STDIN, STDOUT respectively. There is also a prenamed file handle for I/O
errors, STDERR.
The<STDIN > File handle:
When we want to get input
from the user in perl programs we use the STDIN file handle. To get i/p from
STDIN, you enclose the file handle with PERL'S operator for reading lines of
text, the angle operator <>.
Syntax: -$var=<STDIN>; # it
reads only one line
@Var=<STDIN>; # it reads multiple lines
Ex: -#! g:\perl\bin\perl
While ($line=<STDIN>)
{
Print "$line";
Last if ($line eq
"quit\n");
}
The
< STDOUT >File handle:
For output to the standard output device the
screen, perl uses the print function. Print takes two arguments, the file
handle of the I/O channel being printed to, and a string or list of
comma-separated strings. Formatted output can be obtained with printf function.
Syntax: -print STDOUT "whatever
you want to print";
Syntax for
opening a file:
Open (file handler, name of file)
Open (fh,"abc.dat") ------ opens file in read mode.
Open (fh,">bac.dat")
------ opens file in write mode.
Open (fh,">>abc.dat")
------ opens file in append mode.
Ex: read.pl
Open (fh,"abc.dat");
$x=<fh>;
While ($x)
{
Print "$x","\n";
$x=<fh>;
}
Ex: write.pl
Print "Enter your name:";
$Name=<stdin>;
Chop ($name);
Print "Enter your age:";
$Age=<stdin>;
Chop ($age);
$d="#", $n="\n";
$Rec=$name. $d. $age.$n;
Open (fh,">wrec.dat");
Print fh
$wrec;
# Close (fh);
9. WORKING WITH DIRECTORIES:-
Directories are special
files that contain information about the other directories and files. PERL
provides several functions to access and use information in a directory.
To open a directory: -
For opening a directory,
directory handle is set up and opendir () function is used.
Syntax:-opendir (DIRHANDLE,”dirname”);
To close a directory: -
The close () can be called to
close the directory when it is no longer in use.
Syntax: -close (DIRHANDLE);
Creating a directory: -
The mkdir () is used to
create a directory as in Unix. To create a directory calls the mkdir () with
argument.
Syntax: -mkdir (“directory
name”);
To remove a directory:-
To remove a directory calls
the rmdir () with an argument. The rmdir () does not remove the directory if it
contains any files.
Syntax: -rmdir (“directory name”);
To go to the beginning of the
directory: -
To go beginning of the directory after having read
Some
of the entries. To do so, call the rewinddir ().
Syntax: -rewinddir
(DIRHANDLE);
Reading the contents of the
directory: -
After the directory is open,
its contents can be read using the readdir (). For example, to read all the
directory entries into an array with a single call to the redder functions.
Syntax: -@file list=readdir
(DIRHANDLE);
10. DATABASE PROGRAMMING IN PERL:-
Perl
language provides many features for data base programming.
UNIX ENVIRONMENT:
On
many unix systems, there is a system database feature called this database lets
you store information in key-value pairs.
In a pair of disk files Perl
provides access to this database through a hash that is associated with the
DBM. Via hash you can add data to DBM
,and edit and delete data in the DBM.
The
disadvantage in the DBM system is that it works only with a key value
pairs,which occurs often.
To store more complex data Random Access to Files is
recommended.
WINDOWS ENVIRONMENT:
In
windows environment ,database programming is done using
Microsoft’s ActiveX Data Objects
and Open Database Connectivity.
ActiveX Data Object is an interface
that exposes a set of objects that provide access to Msaccess files, or SQL
server.
ODBC is a popular data access method
that is implemented in perl using
win32::ODBC module.Using this module you can connect to any ODBC compliant relational database.
11. CONCLUSION:-
Perl basically evolved for extraction and report generation operations.
Due to its powerfulness it is widely used in string manipulations I/O and
system tasks. Now perl is widely used for writing C.G.I scripts.