Perl Cheatsheet

Perl(Practical Extraction and Report Language) is especially designed for text processing by Larry Wall. Perl is a high level programming language and hence one can easily undertand Perl as the programs are in simple english.

Basics

Sample program

print "Hello World!!"; # to display "Hello World!!"

• print -- to print the data given
• # -- single line comments

Data types

Perl has three basic data types:

1. Scalars
2. Arrays
3. Hashes

$var-name =value; #scalar-variable
@arr-name = (values); #Array-variables
%hashes = (key-value pairs); # Hash-variables 

In Perl, there is no need to explicitly declare variables to reserve memory space. When you assign a value to a variable, declaration happens automatically.

Operators

String Functions

Below are some of the useful string functions in Perl.

Lists

List is a series of scalar values separated by commas and enclosed in round brackets. Lists are immutable.

(); # empty list

(1,2,3,4,5); # integer list

("Hello", "World"); #string list

("happy", 16) # list with different types of data

Hashes

Hash is an unordered set of key/value pairs. They are preceded by %.

%nationalGame = (Australia => 'Cricket',
Japan => 'Wrestling',
NewZealand => 'Rugby',
USA => 'Baseball',
England => 'Cricket');

Arrays

Array is a variable which gives dynamic storage for a list.

my @fruits = qw(Apple Orange Grapes Kiwi Watermelon Banana);

Array Operations

Conditional Statements

1. If

if(conditional-expression)
{
    #code
}

2. If-else

if(conditional-expression)
{
    #code
} else {
    #code
}

3. If-else-if ladder

if(conditional-expression-1)
{
    #code
} elsif(conditional-expression-2) {
    #code
} elsif(conditional-expression-3) {
    #code
}
....
else {
    #code
}

4. Nested-If

Nested-Ifs represents if block within another if block.

if(conditional-expression-1) {    
     #code    
          if(conditional-expression-2) {  
             #code
             if(conditional-expression-3) {
                 #code
             }  
    }    
}

5. Unless

Unless is similar to If and is equivalent to if-not.

statement unless(condition-expression);

#or

unless(condition-expression){
   #code 
}

6. Unless-else

unless(condition-expression){
  # unless code
}else{
  # else code
}

7. Given

Given is similar to Switch in other programming languages.

given(conditional-expression){    
when(value1){#code}
when(value2){#code}
when(value3){#code}
...
} 

Loops

1. For

for(Initialization; Condition; Increment/decrement){  
#code  
} 

#or

for (range){
  #code
}

2. While

while(condition){  
#code 
}  

3. Do-while

do{  
#code 
} while(condition); 

4. Until

until(conditional-expression){
   # code
}

5. Do-Until

do{
   # code
}until(condition-expression)

Classes and Objects

Class

package className; 

Objects

$object = new className( Attributes);

Methods

sub methodName{
  #code
}

Sub-routines

sub SubName  [PROTOTYPES] [ATTRIBUTES] { # defining a sub-routine
  #code
}

&SubName; # calling a sub-routine
#or
SubName(argument-list); # calling a sub-routine, argument-list is optional

Example

sum(10,20);

sub sum() {
   $sum = 0;

   foreach $item (@_) {
      $sum += $item;
   }
print "sum is: $sum"
  
}

Files

Opening a file

open(filehandle,mode,filename)

Example

open(FH, '<', 'c:\sample.txt');

Closing a file

close(FH);