Perl is a
general-purpose programming language originally developed for text manipulation
and now used for a wide range of tasks including system administration,
web development,
network programming, GUI development, and more.
First Perl Program
Interactive Mode
Programming
You can use Perl interpreter with -e option at command line, which
lets you execute Perl statements from the command line. Let's try something at
$ prompt as follows −
Comments in Perl
Comments in any
programming language are friends of developers. Comments can be used to make
program user friendly and they are simply skipped by the interpreter without
impacting the code functionality. For example, in the above program, a line
starting with hash #is a comment.
Whitespaces in Perl
A Perl program does not care about whitespaces. Following program
works perfectly fine −
Single and Double Quotes in Perl
You can use double quotes or single quotes around literal strings as
follows −
Escaping Characters
Perl uses the backslash (\) character to escape any type of
character that might interfere with our code. Let's take one example where we
want to print double quote and $ sign −
Data Types
Perl is a loosely
typed language and there is no need to specify a type for your data while using
in your program. The Perl interpreter will choose the type based on the context
of the data itself.
Perl has three basic data types − scalars, arrays of scalars, and hashes of scalars, also
known as associative arrays. Here is a little detail about these data types.
S.N.
|
Types and Description
|
1
|
Scalar −
Scalars are simple
variables. They are preceded by a dollar sign ($). A scalar is either a
number, a string, or a reference. A reference is actually an address of a
variable, which we will see in the upcoming chapters.
|
2
|
Arrays −
Arrays are ordered
lists of scalars that you access with a numeric index which starts with 0.
They are preceded by an "at" sign (@).
|
3
|
Hashes −
Hashes are unordered
sets of key/value pairs that you access using the keys as subscripts. They
are preceded by a percent sign (%).
|
Example
Variables
Variables are the
reserved memory locations to store values. This means that when you create a
variable you reserve some space in memory.
Based on the data type
of a variable, the interpreter allocates memory and decides what can be stored
in the reserved memory. Therefore, by assigning different data types to
variables, you can store integers, decimals, or strings in these variables.
Creating Variables
Perl variables do not
have to be explicitly declared to reserve memory space. The declaration happens
automatically when you assign a value to a variable. The equal sign (=) is used
to assign values to variables.
Keep a note that this
is mandatory to declare a variable before we use it if we use use strict
statement in our program.
The operand to the left of the = operator is the name of the
variable, and the operand to the right of the = operator is the value stored in
the variable. For example −
$age = 25; # An integer assignment
$name = "John Paul"; # A string
$salary = 1445.50; # A floating point
Scalar Variables
A scalar is a single
unit of data. That data might be an integer number, floating point, a
character, a string, a paragraph, or an entire web page. Simply saying it could
be anything, but only a single thing.
Here is a simple example of using scalar variables −
Example
Array Variables
An array is a variable
that stores an ordered list of scalar values. Array variables are preceded by
an "at" (@) sign. To refer to a single element of an array, you will
use the dollar sign ($) with the variable name followed by the index of the
element in square brackets.
Here is a simple example of using array variables −
Example
Hash Variables
A hash is a set of
key/value pairs. Hash variables are preceded by a percent (%) sign. To refer to
a single element of a hash, you will use the hash variable name followed by the
"key" associated with the value in curly brackets.
Here is a simple example of using hash variables −
Example
Array
An array is a variable
that stores an ordered list of scalar values. Array variables are preceded by
an "at" (@) sign. To refer to a single element of an array, you will
use the dollar sign ($) with the variable name followed by the index of the
element in square brackets.
Here is a simple example of using the array variables −
Example
Array Creation
Array variables are prefixed with the @ sign and are populated using
either parentheses or the qw operator. For example −
@array = (1, 2,
'Hello');
@array = qw/This is an
array/;
Array Size
The size of an array can be determined using the scalar context on
the array - the returned value will be the number of elements in the array −
@array = (1,2,3);
print "Size:
",scalar @array,"\n";
Example
Perl Conditional Statements
Perl programming
language provides the following types of conditional statements.
Statement
|
Description
|
An if
statement consists of a boolean expression followed by one or more
statements.
|
|
An if
statement can be followed by an optional else statement.
|
|
An if
statement can be followed by an optional elsif statement and
then by an optional else statement.
|
|
An unless
statement consists of a boolean expression followed by one or more
statements.
|
|
An unless
statement can be followed by an optionalelse statement.
|
|
An unless
statement can be followed by an optionalelsif statement and then by
an optional else statement.
|
|
With the latest
versions of Perl, you can make use of the switch statement. which
allows a simple way of comparing a variable value against various conditions.
|
Perl IF Statement
Syntax
The syntax of an if statement in Perl programming language is −
if(boolean_expression){
# statement(s) will execute if the given
condition is true
}
Example
Perl IF...ELSE statement
Syntax
The syntax of an if...else statement in Perl programming language is
−
if(boolean_expression){
# statement(s) will execute if the given
condition is true
}else{
# statement(s) will execute if the given
condition is false
}
Example
Perl IF...ELSIF statement
Syntax
The syntax of an if...elsif...else statement in Perl programming
language is −
if(boolean_expression
1){
# Executes when the boolean expression 1 is
true
}
elsif(
boolean_expression 2){
# Executes when the boolean expression 2 is
true
}
elsif(
boolean_expression 3){
# Executes when the boolean expression 3 is
true
}
else{
# Executes when the none of the above
condition is true
}
Example
Switch statement
Syntax
The synopsis for a switch statement in Perl programming language is
as follows −
use Switch;
switch(argument){
case 1 { print "number 1" }
case "a" { print "string a" }
case [1..10,42] { print "number in list" }
case (\@array) { print "number in list" }
case /\w+/ { print "pattern" }
case qr/\w+/ { print "pattern" }
case (\%hash) { print "entry in hash" }
case (\&sub) { print "arg to subroutine" }
else { print "previous case not
true" }
}
Perl - Loops
Perl programming
language provides the following types of loop to handle the looping
requirements.
Loop Type
|
Description
|
Repeats a statement
or group of statements while a given condition is true. It tests the
condition before executing the loop body.
|
|
Repeats a statement
or group of statements until a given condition becomes true. It tests the
condition before executing the loop body.
|
|
Executes a sequence
of statements multiple times and abbreviates the code that manages the loop
variable.
|
|
The foreach loop
iterates over a normal list value and sets the variable VAR to be each
element of the list in turn.
|
|
Like a while
statement, except that it tests the condition at the end of the loop body
|
|
You can use one or
more loop inside any another while, for or do..while loop.
|
Perl while Loop
Syntax
The syntax of a while loop in Perl programming language is −
while(condition)
{
statement(s);
}
Example
Perl for Loop
Syntax
The syntax of a for loop in Perl programming language is −
for ( init; condition;
increment ){
statement(s);
}
Example
Perl foreach Loop
Syntax
The syntax of a foreach loop in Perl programming language is −
foreach var (list) {
...
}
Example
Perl do...while Loop
Syntax
The syntax of a do...while loop in Perl is −
do
{
statement(s);
}while( condition );
Example
Perl nested Loop
Syntax
The syntax for a nested for loop statement in Perl is as follows −
for ( init; condition;
increment ){
for ( init; condition; increment ){
statement(s);
}
statement(s);
}
Example
Perl string manipulations
String concatenation
To concatenate two
strings together, just use the . dot:
$a . $b;
$c = $a . $b;
$a = $a . $b;
$a .= $b;
Example
Substring extraction
The counterpart of
string concatenation is substring extraction. To extract the substring at
certain location inside a string, use the substr function:
$second_char =
substr($a, 1, 1);
$last_char =
substr($a, -1, 1);
$last_three_char =
substr($a, -3);
Example
Substring search
In order to provide
the second argument to substr, usually you need to locate the substring to be
extracted or replaced first. The index function does the job:
$loc1 = index($string,
"abc");
$loc2 = index($string,
"abc", $loc+1);
print "not
found" if $loc2<0;
This function returns the square root of EXPR, or $_ if omitted. Most of the time, this function returns a floating point number.
Syntax
Following is the simple syntax for this function −
sqrt EXPR
sqrt
Example
The join function
Although not actually
a pattern matching function, the counterpart of the split function is the join
function, which connects all members in an array with some fixed strings:
my $string = join
" ", @words; # this time the " " is just what it is, one
space character
sprintf Function
Syntax
Following is the simple syntax for this function −
sprintf FORMAT, LIST
Example
Following is the example code showing its basic usage −
