Scalar: It is denoted by $ symbol. Variable can be a number or a string.

Array: Denoted by @ symbol prefix. Arrays are indexed by numbers.

The namespace for these types of variables is different. For Example: @add, $add. The scalar variables are
in one table of names or namespace and it can hold single specific information at a time and array variables
are in another table of names or namespace. Scalar variables can be either a number or a string.

“Emacs” or “vi” can be used in UNIX and in Windows NT we can use “notepad”. In Macintosh we can use
MacPerl’s text editor or any other text editor and in OS/2, e or epm can be used

Inheritance feature of Perl provides code reusability. In inheritance, the child class can use the methods
and property of parent class

• The -w Command-line option: It will display the list if warning messages regarding the code.
• strict pragma: It forces the user to declare all variables before they can be used using the my() function.
• Using the built-in debugger: It allows the user to scroll through the entire program line by line.

Yes, Perl has objects and it doesn't force you to use objects. Many object oriented modules can be used
without understanding objects. But if the program is too large then it is efficient for the programmer to make
it object oriented.

Yes, we can load binary extension dynamically but your system supports that. If it doesn't support, then you
can statically compile the extension.

-w (argument shows warning)

-d (use for debug)

-c (which compile only not run)

-e (which executes)

We can also use combination of these like:

-wd

The scalar: It can hold one specific piece of information at a time (string, integer, or reference). It starts
with dollar $ sign followed by the Perl identifier and Perl identifier can contain alphanumeric and
underscores. It is not allowed to start with a digit. Arrays are simply a list of scalar variables.

Arrays: Arrays begin with @ sign.

Associative arrays: It also frequently called hashes, are the third major data type in Perl after scalars and
arrays. Hashes are named as such because they work very similarly to a common data structure that
programmers use in other languages--hash tables. However, hashes in Perl are actually a direct language
supported data type.

“use”

1. The method is used only for the modules (only to include .pm type file)

2. The included objects are verified at the time of compilation.

3. We don’t need to specify the file extension.

4. loads the module at compile time.

“require”

1. The method is used for both libraries and modules.

2. The included objects are verified at the run time.

3. We need to specify the file Extension.

4. Loads at run-time.

suppose we have a module file as “Module.pm”

use Module;

or

require "Module.pm";

(will do the same)

In Perl, the following guidelines must follow by the modules:

The file name of a module must the same as the package name.

The name of the package should always begin with a capital letter.

The entire file name should have the extension ".pm".

In case no object oriented technique is used the package should be derived from the Exporter class.

Also if no object oriented techniques are used the module should export its functions and variables to the
main namespace using the @EXPORT and @EXPOR_OK arrays (the use directive is used to load the
modules).

Every Perl program must be passed through the Perl interpreter in order to execute.

The interpreter compiles the program internally into a parse tree. Any words, spaces, or marks after a
pound symbol will be ignored by the program interpreter. After converting into parse tree, interpreter
executes it immediately. Perl is commonly known as an interpreted language, is not strictly true. Since the
interpreter actually does convert the program into byte code before executing it, it is sometimes called an
interpreter/compiler. Although the compiled form is not stored as a file.

If you need faster execution the Perl will provide you that requirement. There a lot of flexibility in
programming if you want to develop a web based application. We do not need to buy the license for Perl
because it is free. We can use CPAN (Comprehensive Perl Archive Network), which is one of the largest
repositories of free code in the world.

Arithmetic operators

+, - ,*

Assignment operators:

+= , -+, *=

Increment/ decrement operators:

++, --

String concatenation:

‘.’ operator

comparison operators:

==, !=, >, =

Logical operators:

&&, ||, !

The command line arguments in Perl are stored in an array @ARGV.

$ARGV[0] (the first argument)

$ARGV[1] (the second argument) and so on.

$#ARGV is the subscript of the last element of the @ARGV array, so the number of arguments

on the command line is $#ARGV + 1

The command line arguments in Perl are stored in an array @ARGV.

$ARGV[0] (the first argument)

$ARGV[1] (the second argument) and so on.

$#ARGV is the subscript of the last element of the @ARGV array, so the number of arguments

on the command line is $#ARGV + 1

When we use –w, it gives warnings about the possible interpretation errors in the script. Strict tells Perl to
force checks on the definition and usage of variables. This can be invoked using the use strict command. If
there are any unsafe or ambiguous commands in the script, this pragma stops the execution of the script
instead of just giving warnings. When used –t, it switches on taint checking. It forces Perl to check the
origin of variables where outside variables cannot be used in sub shell executions and system calls

Terms have the highest precedence in Perl. Terms include variables, quotes, expressions in parenthesis etc.
List operators have the same level of precedence as terms. Specifically, these operators have very strong
left word precedence.

Scalars ($): It stores a single value.

Arrays (@): It stores a list of scalar values.

Hashes (%): It stores associative arrays which use a key value as index instead of numerical indexes

The -n and -p options are used to wrap scripts inside loops. The -n option makes the Perl execute the script
inside the loop. The -p option also used the same loop as -n loop but in addition to it, it uses continue. If
both the -n and -p options are used together the -p option is given the preference.

The -i option is used to modify the files in-place. This implies that Perl will rename the input file
automatically and the output file is opened using the original name. If the -i option is used alone then no
backup of the file would be created. Instead -i.bak causes the option to create a backup of the file.

In Perl, the symbol table is a hash that contains the list of all the names defined in a namespace and it
contains all the functions and variables.

When a hash value is referenced, it is not created. It is only created once a value is assigned to it. The
contents of a hash have no literal representation. In case the hash is to be filled at once the unwinding of
the hash must be done. The unwinding of hash means the key value pairs in hash can be created using a
list, they can be converted from that as well. In this conversion process the even numbered items are placed
on the right and are known as values. The items placed on the left are odd numbered and are stored as
keys. The hash has no defined internal ordering and hence the user should not rely on any particular
ordering.

In Perl, aliases are considered to be faster than references because they do not require any dereferencing.

Whenever a variable is used in Perl, it occupies some memory space. Since the computer has limited
memory the user must be careful of the memory being used by the program.

On execution of above program, after reading a file it will print the first word of each line into another file.
If the files are too large then the system would run out of memory. To avoid this, the file can be divided
into sections.

It is defined as the type of return value that is expected. You can use a single function that returns different
values.

$-Scalar variables

%-Hash variables

@-arrays

&-subroutines

Type globs-*myvar stands for @myvar, %myvar.

In CPAN, the CGI and DBI are very common packages

There are more development tools for C than for PERL. PERL execute slower than C programs. Perl
appears to be an interpreted language but the code is complied on the fly. If you don't want others to use
your Perl code you need to hide your code somehow unlike in C. Without additional tools it is impossible to create an executable of a Perl program

It is called as "greedy match" because Perl regular expressions normally match the longest string possible.

‘&myvariable’ is used to call a sub-routine and ‘&’ is used to identify a sub-routine.

In Perl, ‘->’ symbol is an infix dereference operator. if the right hand side is an array subscript, hash key or
a subroutine, then the left hand side must be a reference.

We can eliminate the new line character by using ‘chomp’. It can used in many different scenarios.

The ‘$_’ is a default variable in Perl and $_ is known as the "default input and pattern matching space

Perl is a programming language designed for text processing. It runs on various platforms Windows, Mac
OS and various versions of UNIX.

To print a string, you need to observe the following -

A string should have double Quotesà “…..”

A special character referred as “new line” à \n

A semicolon at the end of the program à ;

Example: print “Hello, World!\n”;

To provide code re-usability in PERL inheritance feature is used. In Inheritance, the child class can use the
methods and property of the parent class.

Die will print a message to the std err before ending the program while Exit will simply end up the
program.

To filter the list and return only those elements that match certain criteria Perl grep function is used.

The syntax used in Perl is

a) grep BlOCK LIST

b) grep ( EXPR, LIST )

Scalar in Perl means a single entity like a number or string. So, the Java concept of int, float, double and
string equals to perls scalar and the numbers and strings are exchangeable. While scalar variable is used to
store scalar data. It uses $ sign and followed by one or more alphanumeric characters or underscore. It is a
case sensitive.

In Perl, the arrow - > symbol is used to create or access a particular object of a class.

You can express string in Perl in many ways

For instance “this is jobsmate.”

qq/this is jobsmate like double quoted string/

qq^this is jobsmate like double quoted string^

q/this is jobsmate /

q&this is jobsmate&

q(this is jobsmate)

REQUIRE statement: It is used to import functions with a global scope such that their objects and
functions can be accessed directly

Example: Require Module,

Var=module::method(); //method called with the module reference

USE statements are interpreted and are executed during parsing, while during run time the require
statements are executed.

Example: Use Module

Var=method(); //method can be called directly

• Chop function eliminates the last character from expr, each element of the list
• Chomp function eliminates the last character from an expr or each element of the list if it matches the value of $/. It is considered better than chop as it only removes the character if there is a match.

CPAN means Comprehensive Perl Archive Network, a large collection of Perl software and
documentation.

In Perl, Polymorphism means the methods defined in the base class will always over-ride the methods
defined in the parent class.

There are two ways through which private values can be obtained inside a subroutine or block

Local Operator: On global variables only this operator can operate. The value of the private variable is
saved on the Local Operator and makes the provision to restore them at the end of the block

My Operator: To define or create a new variable this operator can be used. Variable that is created by My
Operator will always be declared private to block inside which it is defined.

STDIN: The STDIN file handle is used to read from the keyboard

STDOUT: It is used to write into the screen or another program

STDERR: It is also used to write into a screen. STDERR is a standard error stream that is used in Perl.

The closure is a block of code that is used to capture the environment where it is defined. It particularly
captures any lexical variables that block consists of and uses in an outer space.

One liner is one command line programs and can be executed from the command line immediately.

For example,

# run program under the debugger

perl-d my_file

An Ivalue is a scalar value which can be used to store the result of any expression. Usually, it appears at
the left-hand side of the expression and represent a data space in memory.

• Grooving & Shortening of arrays can be executed directly by giving a non-existent index to which Perl automatically adjust the array size

• Splicing of arrays copies and removes or replaces elements from an array using the position identified in the spliced function instead of extracting into another array

To tell how many characters are there in a string, length () function is used.

Using a particular prefix when you dereference a variable, they are called prefix dereferencer.

• $- Scalar variables
• %-Hash variables
• @-Arrays
• &-Subroutines
• Type globs-*myvar stands for @myvar, %myvar

The Return Value function returns a reference to an object blessed into CLASSNAME.

• Can make perl files self executable by making first line as #! /bin/perl.
• The extension tells the kernel that the script is a perl script and the first line tells it where to look for perl.

The -w switch tells perl to produce extra warning messages about potentially dangerous constructs.

The advantage of Perl is that you don't have to compile create object file and then execute.

Note: The pound sign "#" is the symbol for comment entry. There is no multiline comment entry , so you
have to use repeated # for each line.

Forces EXPR to be interpreted in scalar context and returns the value of EXPR.

Scalar Functions:

• Chop
• Chomp
• Defined
• Undef
• Uc,lc,ucfirst,lcfirst
• My and local and our
• Ref – after reference
• Return
• Reverse
• Index
• Substr
• Context – not a keyword
• Legnth