Perl is a general purpose programming language invented by Larry Wall in 1987. It can be used for web development, system scripting, and data processing. Key points:
- Perl can run on both UNIX and Windows systems, and code developed on one system can be portable to the other.
- Common uses of Perl include web development, like writing CGI scripts for websites, and processing large data sets in fields like finance, manufacturing, and genetics.
- Perl supports scalar and list data types. Scalar variables start with $ and can hold numbers or strings. Lists are collections of scalar data that can be stored in array variables prefixed with @.
- Perl includes control structures like if/else, for loops
1. Introducing to Perl –
Perl stands for Practical Extraction and Reporting Language. Perl
is a general purpose, high level, interpreted and dynamic
computer programming language with a vast number of uses.
Invented By –
Perl was invented by Larry Wall, a linguist working as a systems
administrator at NASA in 1987. From the beginning, Perl was
used as a general-purpose UNIX scripting language to help
processing reports faster and easier. Since then Perl has
undergone a lot of modification and improvements to become
popular among developer community. Even though Perl has far
surpassed its first invention, Larry Wall is still developing the
core language with the newest version of Perl now is Perl.
2. Use of Perl –
Today Perl is found in varied applications such as
finance, manufacturing, genetics, the military etc to process large data
sets. Perl is used to be one of the most popular languages for
developing web applications. At that time, Perl is used to write CGI
scripts. You can find Perl in large projects such as Bugzilla, movable
Type and other high-traffic websites such as Amazon.com, Ebay, Live
Journal and Craigslist.
Portability –
Perl run well on UNIX and Windows systems. If you develop Perl for
UNIX system, it can be portable to Windows system as well. This
tutorial is only for Windows.
Perl Development Environment
Download and install Active Perl
You first need to download Active Perl the latest version from
http://www.activestate.com/activeperl/.
3. First Program in Perl
First, you open the Open Perl IDE and type the following code:
#!/usr/bin/perl
print "vande mataramn";
You can save the Perl source code file with any name you want. It
is highly recommended that Perl source code file should has
extension .pl or .ple (Perl executable).
When you click Run > Run or press F9, the program will launch
and print the message “vande mataram”
The first line of the program is a special comment. Comments in
Perl program start from the pound sign (#) to the rest of line.
There is no sign for block comment in Windows. On UNIX
systems, two characters #! starting in a line indicates the
program is stored in the file /usr/bin/perl
4. Variables in perl
Perl Scalar Variables
Scalar data is the one of the most basic and simplest data in Perl. Scalar
data can be number or string In Perl . Scalar variable starts with dollar
sign ($) followed by Perl identifier. Perl identifier can contain
alphanumeric and underscores. It is not allowed to start with a digit.
$x = 3;
Let's take a look in more details how we use scalar variables with
number and string.
Number
Perl uses double-precision floating point values for calculation. Perl
internally cheats integer as floating-point value. Perl uses literal to
define number and with minus sign (-) to define negative number.
Here is the code snippet to demonstrate scalar variable which holds
number in Perl:
5. #floating-point values
$x = 3.14;
$y = -2.78;
#integer values
$a = 1000;
$b = -2000;
Perl also accepts string literal as a number for example:
$s = "2000"; # similar to $s = 2000;
In above case $s can be use as a number when calculation even though
it is a string.
6. String
Perl defines string as a sequence of characters. The shortest
string contains no character or null string. The longest string can
contain unlimited characters which is only limited to available
memory of your computer. Similar to number, Perl represents
string by literal. A string can be wrapped in a single or double
quotes. For example:
$str = "this is a string in Perl".
$str2 = 'this is also as string too'.
We defined two scalar variables which hold string in double
quotes and sing quotes
Operations on scalar variables
Perl uses arithmetic operators as another languages like C/C++
and Java. Here is the code snippet to demonstrate all of operators
on numerical scalar variables.
7. $x = 5 + 9; # Add 5 and 9, and then store the result in $x
$x = 30 - 4;# Subtract 4 from 30
# and then store the result in $x
$x = 3 * 7; # Multiply 3 and 7 and then store the result in $x
$x = 6 / 2; # Divide 6 by 2
$x = 2 ** 8;# two to the power of 8
$x = 3 % 2; # Remainder of 3 divided by 2
$y = ++$x; # Increase $x by 1 and store $x in $y
$y = $x++; # Store $x in $y then increase $x by 1
$y = --$x; # Decrease $x by 1 and then store $x in $y
$y = $x--; # Store $x in $y then decrease $x by 1
$x = $y; # Assign $y to $x
8. $x += $y; # Add $y to $x
$x -= $y; # Subtract $y from $x
$x .= $y; # Append $y onto $x
For string Perl use full stop (.) for concatenating strings and (x)
for repeating a string.
x = 3;
$c = "he ";
$s = $c x $x;
$b = "bye"; # $c repeated $x times
print $s . "n"; #print s and start a new line
# similar to
print "$sn";
$a = $s . $b; # Concatenate $s and $b
9. For print
$a = 10;
Print $a;
Perl If Statement
In this tutorial, you will learn how to use Perl if control structure to
write simple logic in code.
Perl groups statements into block of code or block. A block is
surrounded by a pair of curly braces and can be nested within a block.
{ #statements here
{ # nested block
# statements here
}
}
10. If control structure is used to execute a block of code based on a
condition in Perl program. The syntax of If control structure is as
follows:
if(condition){
statements;
}
If the condition is true the statements inside block will be
executed, for example:
$x = 10;
$y = 10;
if($x == $y){
print "$x is equal to $y";
}
11. If you need an alternative choice, Perl provides if-else control
structure as follows:
if(condition){
if-statements;
}
else{
else-statements;
}
If the condition is false the else-statements will be executed.
Here is the code example:
$x = 5;
$y = 10;
if($x == $y)
12. print "x is equal to y";
}
else{
print "x is not equal to y";
}
Perl also provides if-else-if control structure to make multiple choices
based on conditions.
if(condition1){
}
else if(condition2){
}
else if(condition3){
}
...
else{
}
13. For loop
you will learn how to interate a block of code multiple times by
using Perl for loop statement.
In order to run a block of code iteratively, you use Perl for
statement. The Perl for statement is used to execute a piece of
code over and over again. The Perl for statement is useful for
running a piece of code in a specific number of times. The
following illustrates Perl for statement syntax:
1
for(initialization; test; increment){
2
statements;
3
}
14. There are three elements in the for statement - initialization, test and
increment - are separated by semicolons. Perl does the following
sequence actions:
Step 1. The initialization is expression is evaluated - you can initialize
counter variable here.
Step 2. The test expression is evaluated. If it is true, the block -
statements - will be executed.
Step 3. After the block executed, the increment is performed and test is
evaluated again. The process go to step 2 until the test expression is
false. If it is never false, you encounter with a indefinite loop.
Here is a code snippet to print a message 10 times.
1
for($counter = 1; $counter <= 10; $counter++){
2
print "for loop #$countern";
3
}
15. Perl While loop
you will learn another control flow statement called
Perl while loop to execute a piece of code in a number
of times based on a specific Boolean condition.
Perl While statement is a Perl control structure that
allows to execute a block of code repeatedly. The Perl
while statement is used when you want to check a
Boolean condition before making a loop.
The following illustrates the Perl while statement
syntax:
17. List and Array variables
Scalar variable allows you to store single element such
as number or string. When you want to manage a
collection or a list of scalar data you use list. Here are
some examples of lists.
("Perl","array","tutorial");
(5,7,9,10);
(5,7,9,"Perl","list");
(1..20);
();
18. We have five lists. In the line 1 we have a list which
contains three string. Line 2 we have a list which
contains 4 integer. Line 3 we have a list which contains
3 integer and 2 strings. Line 4 we have a list of 20
elements. A pair of period (..) is called range operator.
Line 5 we have an empty list. Each scalar data in the
list is called list element.
To store list to use throughout program you need array
variable. Array variable is used to hold a list data.
Different from scalar variable, array variable are
prefixed with at sign(@). For example we have five
array variables to store five lists above as follows:
19. @str_array = ("Perl","array","tutorial");
@int_array = (5,7,9,10);
@mix_array = (5,7,9,"Perl","list");
@rg_array = (1..20);
@empty_array = ();
Array element can be accessed by using indices starting
from zero (0). Perl uses square bracket to specify the index.
For example to get the second element of array @str_array
we use expression as follows:
$str_array[1];
Be noticed that the dollar sign ($) is used instead of at sign
(@). It is understandable that array element is scalar so ($)
sign is used instead.
20. Operations on array
You can add or remove elements to/from an array. Here is a
function list which allows you to do common operations on
array:
push(@array,$element) add $element to the end of array @array
pop(@array) remove the last element of array @array and returns
it.
unshift(@array,$element) add $element to the start of array
@array
shift(@array) remove the first element from array @array and
returns it.
Here is the code snippet to demonstrate each function above:
21. @int =(1,3,5,2);
push(@int,10); #add 10 to @int
print "@intn";
$last = pop(@int); #remove 10 from @int
print "@intn";
unshift(@int,0); #add 0 to @int
print "@intn";
$start = shift(@int); # add 0 to @int
print "@intn";
Be noticed that the line 4, 7, 10 and 14 is used to print the array.
