Perl

Let’s Learn PerlAn introduction to Perl

Sreejith SNLP Process Analyst365Media Pvt. Ltd.

[email protected]

January 22, 2011

Sreejith S Let’s Learn Perl

Just a word about me !!

Working in Natural Language Processing (NLP), Machine Learning,Data Mining

Passionate about Free and Open source :-)

Works for 365Media Pvt. Ltd. Coimbatore India.


What’s Perl ??

Practical Extraction and Reporting Language

Perl is a Portable Scripting Language

Fast and easy text processing capability

Fast and easy file handling capability

It aims to be practical (easy to use, efficient, complete) rather thanbeautiful (tiny, elegant, minimal)

Perl was developed by Larry Wall.


What’s Perl ??








What’s Perl ??








What’s Perl ??








What’s Perl ??








What’s Perl ??








To install...

Perl Comes by Default on Linux, Cygwin, MacOSX

www.perl.com has rpm’s for Linuxwww.activestate.com has binaries for Windows

Latest Version is 5.10To check if Perl is working and the version number

perl -v or perl -version


To install...


www.perl.com has rpm’s for Linux

www.activestate.com has binaries for Windows




To install...






To install...



Latest Version is 5.10

To check if Perl is working and the version number



To install...






To install...







Basic Syntax of Perl

Comments

begin with #dont try to use // or /* ... */

Print

print is simple function to display/output something onmonitor/stdoute.g :- print “hello world“;

Statement terminator ;

All Statements end with ; like C language

Delimiter

{} delimit blocks, loops, subroutines

No main() function

Top-down programming approach



Comments

begin with #

dont try to use // or /* ... */

Print




Delimiter


No main() function




Comments


Print




Delimiter


No main() function




Comments


Print




Delimiter


No main() function




Comments


Print

print is simple function to display/output something onmonitor/stdout

e.g :- print “hello world“;



Delimiter


No main() function




Comments


Print




Delimiter


No main() function




Comments


Print




Delimiter


No main() function




Comments


Print




Delimiter


No main() function




Comments


Print




Delimiter


No main() function




Comments


Print




Delimiter


No main() function




Comments


Print




Delimiter


No main() function




Comments


Print




Delimiter


No main() function



Structure of a Perl Program

#! /usr/bin/perl -w

It tells where to find Perl

.pl extension is optional but is commonly used

You can write perl programs without extension also.

-w switches on warning : not required but a really good idea



#! /usr/bin/perl -w







#! /usr/bin/perl -w







#! /usr/bin/perl -w







#! /usr/bin/perl -w






Customary Hello World Program

#! /usr/bin/perl -w

print "Hello World!\n";

Save this as hello.pl

To run the program

perl hello.pl or perl hello



#! /usr/bin/perl -w



To run the program




#! /usr/bin/perl -w



To run the program




#! /usr/bin/perl -w



To run the program



Variables

Variables are memory location to store information.

Variables are type less

There is no data type like int,char,float

Variables do not need to be declared

Every variable is a string

Variable type is decided at run timeDepending on the context will be treated as int, float etc.

There are 4 kinds of variables namely

ScalarsListsArraysHashes.


Variables










Variables










Variables










Variables










Variables






Variable type is decided at run time

Depending on the context will be treated as int, float etc.




Variables










Variables










Variables








Scalars

ListsArraysHashes.


Variables








ScalarsLists

ArraysHashes.


Variables








ScalarsListsArrays

Hashes.


Variables










Scalars

Scalar meaning single value

Name of scalar variable must begin with $ symbol.

next character must a letter orremaining characters: letters, numbers, orname can be up to 255 characters long

Right

$foo, $a, $zebra1, $F87dr df3

Wrong

$24da, $hi&bye, $bar$foo

Examples

$name=”ram”; # in string context$age=30; # in numerical context$value = 4.43; # in float context$foo = Z; # in char context


Scalars




Right


Wrong


Examples



Scalars



next character must a letter or

remaining characters: letters, numbers, orname can be up to 255 characters long

Right


Wrong


Examples



Scalars



next character must a letter orremaining characters: letters, numbers, or

name can be up to 255 characters long

Right


Wrong


Examples



Scalars




Right


Wrong


Examples



Scalars




Right


Wrong


Examples



Scalars




Right


Wrong


Examples



Scalars




Right


Wrong


Examples



Scalars




Right


Wrong


Examples



Scalars




Right


Wrong


Examples



Scalars




Right


Wrong


Examples

$name=”ram”;

# in string context$age=30; # in numerical context$value = 4.43; # in float context$foo = Z; # in char context


Scalars




Right


Wrong


Examples

$name=”ram”; # in string context

$age=30; # in numerical context$value = 4.43; # in float context$foo = Z; # in char context


Scalars




Right


Wrong


Examples

$name=”ram”; # in string context$age=30;

# in numerical context$value = 4.43; # in float context$foo = Z; # in char context


Scalars




Right


Wrong


Examples

$name=”ram”; # in string context$age=30; # in numerical context

$value = 4.43; # in float context$foo = Z; # in char context


Scalars




Right


Wrong


Examples

$name=”ram”; # in string context$age=30; # in numerical context$value = 4.43;

# in float context$foo = Z; # in char context


Scalars




Right


Wrong


Examples

$name=”ram”; # in string context$age=30; # in numerical context$value = 4.43; # in float context

$foo = Z; # in char context


Scalars




Right


Wrong


Examples

$name=”ram”; # in string context$age=30; # in numerical context$value = 4.43; # in float context$foo = Z;

# in char context


Scalars




Right


Wrong


Examples



Variable & Character Interpolation

Perl looks for variables inside strings and replaces them with theirvalue

$name = "Sree";

print "$name is my name\n";

This does not happen when you use single quotes

print ’$name is my name’; and it will print$name is my name

List of character escapes that are recognized when using doublequoted strings

All escape characters are recognized


# It prints Hello World and then a return




$name = "Sree";











$name = "Sree";











$name = "Sree";



print ’$name is my name’; and it will print

$name is my name








$name = "Sree";











$name = "Sree";











$name = "Sree";









Lists

List variables are denoted by symbol ‘()‘

List is just a list of values may be constants, scalars etc

(a,b,c) or ($name,$age,$sex)

The index are specified inside a square bracket ‘[]‘

$first=(a,b,c)[0];

print "$first\n";

List variables can be assigned like this

($name,$age)=(’Raman’,20);

print "name=$name\n";


Lists





$first=(a,b,c)[0];

print "$first\n";





Lists





$first=(a,b,c)[0];

print "$first\n";





Lists





$first=(a,b,c)[0];

print "$first\n";





Lists





$first=(a,b,c)[0];

print "$first\n";





Lists





$first=(a,b,c)[0];

print "$first\n";





Lists





$first=(a,b,c)[0];

print "$first\n";





Arrays

Array variables should have prefix ‘@‘

Arrays are used to store ordered values

Much more dynamic than C/C++

no declaration of size, typecan hold any kind of value, and multiple kinds of values

Array Indexes start at 0

@array=(1,2,3);

To access the whole array, use the whole array

print @array;

To access one element of the array : use $

print $array[0]; # prints : 1


Arrays






@array=(1,2,3);


print @array;




Arrays






@array=(1,2,3);


print @array;




Arrays




no declaration of size, type

can hold any kind of value, and multiple kinds of values


@array=(1,2,3);


print @array;




Arrays






@array=(1,2,3);


print @array;




Arrays






@array=(1,2,3);


print @array;




Arrays






@array=(1,2,3);


print @array;




Arrays






@array=(1,2,3);


print @array;




Arrays






@array=(1,2,3);


print @array;




Arrays






@array=(1,2,3);


print @array;




Operations on Arrays

To append to the end of an array : PUSH

@array=(1,2,3);

push @array,’4’;

print "@array \n";

To remove the last element of the array : POP@array=(1,2,3);

$last=pop @array;

print "last=$last\n";

To prepend to the beginning of an array : UNSHIFT@array=(3,4,5);

unshift @array,’2’;

print "array=@array\n";

To remove the first element of the array : SHIFT@array=(3,4,5);



To access the whole array, use the whole arrayprint @array;

To access one element of the array : use $print $array[0]; # prints : 1



To append to the end of an array : PUSH@array=(1,2,3);


print "@array \n";


$last=pop @array;














print "@array \n";

To remove the last element of the array : POP

@array=(1,2,3);

$last=pop @array;














print "@array \n";


$last=pop @array;














print "@array \n";


$last=pop @array;


To prepend to the beginning of an array : UNSHIFT

@array=(3,4,5);












print "@array \n";


$last=pop @array;














print "@array \n";


$last=pop @array;





To remove the first element of the array : SHIFT

@array=(3,4,5);









print "@array \n";


$last=pop @array;














print "@array \n";


$last=pop @array;









print @array;






print "@array \n";


$last=pop @array;














print "@array \n";


$last=pop @array;















print "@array \n";


$last=pop @array;











Operations on Arrays Contind...

$#array is a special variable containing index of last element.

print $#array; # it will print 2

Another way to find the number of elements in the array:

$array_size = @array;

scalar(@array) is a function to return the size of array






























Hashes

Hash variables will have % as prefix

Key-Value pair

The contents of hash are called values and index is called key. thearray:

%fruits= ( ’apple’=>’red’,’banana’=>’yellow’,

’grape’ =>’black’);

print "colour of apple =$fruits{apple}\n";

Other way of populating a hash

%fruits =(’apple’,’red’,’banana’,’yellow’,

’grape’,’black’);

print "colour of banana =$fruits{banana}\n";

Note the {} instead of [ ] as in the case of array;


Hashes


Key-Value pair











Hashes


Key-Value pair











Hashes


Key-Value pair











Hashes


Key-Value pair











Hashes


Key-Value pair











Hashes


Key-Value pair











Conditionals - IF

The if statement is similar to if in C language, except

flower brace is required even for single statementelse if is noted by elsif (note missing e)

The syntax of if statement is

if (condition) {

}

elsif (condition){

}

else {

}


Conditionals - IF




if (condition) {

}

elsif (condition){

}

else {

}


Conditionals - IF




if (condition) {

}

elsif (condition){

}

else {

}


Conditionals - IF




if (condition) {

}

elsif (condition){

}

else {

}


Control Structures - Loops

Perl supports four main loop types

while, until, for, and foreach

while loop is used to iterate and has syntax similar to C.

$i = 0;

while ( $i <= 1000 )

{

print $i\n;

$i++;

}






$i = 0;

while ( $i <= 1000 )

{

print $i\n;

$i++;

}






$i = 0;

while ( $i <= 1000 )

{

print $i\n;

$i++;

}






$i = 0;

while ( $i <= 1000 )

{

print $i\n;

$i++;

}


Control Structures - Until Loop

The until function evaluates an expression repeatedly until a specificcondition is met

$i = 0;

until ($i == 1000)

{

print $i\n;

$i++;

}


Control Structures - Until Loop

The until function evaluates an expression repeatedly until a specificcondition is met

$i = 0;

until ($i == 1000)

{

print $i\n;

$i++;

}


Control Structures - For Loop

For loop syntax is similar to c.

There are variations

Syntax 1:

for ( $i = 0; $i <= 1000; $i=$i+2 )

{

print $i;

}

Syntax 2:

for $i(0..1000)

{

print $i;

}





Syntax 1:

for ( $i = 0; $i <= 1000; $i=$i+2 )

{

print $i;

}

Syntax 2:

for $i(0..1000)

{

print $i;

}





Syntax 1:

for ( $i = 0; $i <= 1000; $i=$i+2 )

{

print $i;

}

Syntax 2:

for $i(0..1000)

{

print $i;

}





Syntax 1:

for ( $i = 0; $i <= 1000; $i=$i+2 )

{

print $i;

}

Syntax 2:

for $i(0..1000)

{

print $i;

}





Syntax 1:

for ( $i = 0; $i <= 1000; $i=$i+2 )

{

print $i;

}

Syntax 2:

for $i(0..1000)

{

print $i;

}





Syntax 1:

for ( $i = 0; $i <= 1000; $i=$i+2 )

{

print $i;

}

Syntax 2:

for $i(0..1000)

{

print $i;

}


Control Structures - ForEach Loop

Syntax 3:

foreach $i (a,b,c)

{

print uc $i;

}


Control Structures - ForEach Loop

Syntax 3:

foreach $i (a,b,c)

{

print uc $i;

}


Default scalar variable

$ is called default variable

It will be used if no other variable is specified

foreach (a,b,c){

print uc ;

}


Default scalar variable

$ is called default variable

It will be used if no other variable is specified

foreach (a,b,c){

print uc ;

}


Accepting input

Keyboard inputs can be accepted using STDIN

print "enter your name ";

$name=<STDIN>;

chomp $name;

# chomp function is similar to fflush in C.

# It removes trailing newline if any

print "Welcome $name\n";


Accepting input

Keyboard inputs can be accepted using STDIN

print "enter your name ";

$name=<STDIN>;

chomp $name;

# chomp function is similar to fflush in C.

# It removes trailing newline if any

print "Welcome $name\n";


Subroutines

Subroutines can be defined using sub keyword

’@ ’ default array

$v1=10;$v2=20;

add($v1,$v2);

sub add {

($a,$b)=@_;

print $a+$b;

}


Subroutines

Subroutines can be defined using sub keyword

’@ ’ default array

$v1=10;$v2=20;

add($v1,$v2);

sub add {

($a,$b)=@_;

print $a+$b;

}


Scope of variables

By default all variables are global

You can limit scope to a block/sub by using my.

$v1=10; $v2=30; #v1,v2 global

my $i = 10;


Scope of variables

By default all variables are global

You can limit scope to a block/sub by using my.

$v1=10; $v2=30; #v1,v2 global

my $i = 10;


File handling

File handling can be done very easily

To open a file in read mode

open( $fh, < , data.txt);

File reading line by line can be done like

$line=<$fh>;

File writing can be done using print and filehandle like this

print $fh "hello";

Example

open ( $fh, "<", "data.txt" ); #open file read only

open ($fh1,">","udata.txt"); #Open file write mode

while ( $line = <$fh>; ) { #read line by

print "line=$line"; #display content on screen

print $fh1 uc($line); #write upper cased content to new file

}

close($fh);

close($fh1);


File handling





$line=<$fh>;


print $fh "hello";

Example






}

close($fh);

close($fh1);


File handling





$line=<$fh>;


print $fh "hello";

Example






}

close($fh);

close($fh1);


File handling





$line=<$fh>;


print $fh "hello";

Example






}

close($fh);

close($fh1);


File handling





$line=<$fh>;


print $fh "hello";

Example






}

close($fh);

close($fh1);


File handling





$line=<$fh>;


print $fh "hello";

Example






}

close($fh);

close($fh1);


File handling





$line=<$fh>;


print $fh "hello";

Example






}

close($fh);

close($fh1);


File handling





$line=<$fh>;


print $fh "hello";

Example






}

close($fh);

close($fh1);


Some Common String Functions

There are many built in string functions

Convert to upper case

$name = uc($name);

Convert only the first char to upper case

$name = ucfirst($name);

Convert to lower case

$name = lc($name);

Convert only the first char to lower case

$name = lcfirst($name);

Concatenation: ’.’ similar to strcat

$first_name = Larry;

$last_name = Wall;

$full_name = $first_name . . $last_name;





$name = uc($name);




$name = lc($name);





$last_name = Wall;






$name = uc($name);




$name = lc($name);





$last_name = Wall;






$name = uc($name);




$name = lc($name);





$last_name = Wall;






$name = uc($name);




$name = lc($name);





$last_name = Wall;






$name = uc($name);




$name = lc($name);





$last_name = Wall;






$name = uc($name);




$name = lc($name);





$last_name = Wall;






$name = uc($name);




$name = lc($name);





$last_name = Wall;






$name = uc($name);




$name = lc($name);





$last_name = Wall;






$name = uc($name);




$name = lc($name);





$last_name = Wall;






$name = uc($name);




$name = lc($name);





$last_name = Wall;



Some Common Functions

There are many built in functions

Strings to Arrays : split

@array = split( /;/, "Larry;Curly;Moe" );

@array= ("Larry", "Curly", "Moe");

Split into characters

@stooge = split( //, "curly" );

# array @stooge has 5 elements: c, u, r, l, y

Join with any character you want

@array = 10, 20, 30, 40);

$string = join(->, @array);

# string = 10->20->30->40











@array = 10, 20, 30, 40);


# string = 10->20->30->40











@array = 10, 20, 30, 40);


# string = 10->20->30->40











@array = 10, 20, 30, 40);


# string = 10->20->30->40











@array = 10, 20, 30, 40);


# string = 10->20->30->40











@array = 10, 20, 30, 40);


# string = 10->20->30->40











@array = 10, 20, 30, 40);


# string = 10->20->30->40


Web Resource for Perl

Web resources for Perl

www.perl.comwww.perl.orgwww.perlmonks.org


Web Resource for Perl

Web resources for Perl

www.perl.comwww.perl.orgwww.perlmonks.org


Recommended Reading


Questions


Thank You


Date post:	11-May-2015
Category:	Technology
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