perl learning

8/9/2019 Perl Learning

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Practical Extraction and ReportLanguage

Motto: "theres more than one way to do it"

Antony Muthu Pradeep A,

Test Engineer,

Tessolve,

India.


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Introduction

Perl is a general purpose programming languagedevelopedin 1987by Larry Wall. It has become the language of choicefor WWW development, text processing, Internet services,mail filtering, graphical programming, and every other taskrequiring portable and easily-developed solutions.

Perl is interpreted:This means that as soon as you write yourprogram, you can run it -- theres no mandatory compilationphase. The same Perl program can run on Unix, Windows,NT, Mac OS, DOS..


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Perl is collaborative:The CPAN software archivecontains free utilities written by the Perl community, soyou save time.

Perl is free:Unlike most other languages, Perl is notproprietary. The source code and compiler are free,andwill always be free.

Perl is fast:The Perl interpreter is written in C, andmore than a decade of optimisations have resulted in afast executable.


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Where we use Perl?

Text processing: Perls original main use was text processing. It isexceedingly powerful in this regard, and can be used to

manipulate textual data, reports, email, news articles, logfiles or just about any kind of text with great ease.

System administration tasksSystem administration is made easy with Perl. Its

particularly useful for tying together lots of smaller scripts,working with file systems, networking, and so on.


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web programming:Since HTML is just text with built-in formatting, Perlcan be used to process and generate HTML. For many yearsPerl was the de facto language for web development, and is

still very heavily used today.

Database interaction:Perls DBI module makes interacting with all kinds of

databases --- from Oracle down to comma-separated variablefiles --- easy and portable. Perl is increasingly being used towrite large database applications, especially those whichprovide a database backend to a website.


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Creating and running a Perl program

Open Perl IDE is used for writing and debug the

Perl script.

Script Area


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Basic SyntaxBasic Syntax

Put the following in the first line of the script

#!/usr/bin/perl ( optional)

# is used for commenting the line

Each line should end with a semicolon

Save the program in any name with a .pl


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output

compile

Run


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Perl have three types of data types, they are

Perl Data Types

Data Type Starts with Pronounced

Scalar $Array @ atHash % percentage

dollor


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Scalar Variables:

Scalar variables are simple variables containing onlyone element. a string, a number, or a reference.

Eg:my $name = "Arthur";my $whoami = Just Another Perl Hacker;

my $meaning_of_life = 42;

my $number_less_than_1 = 0.000001;my $very_large_number = 3.27e17;my $value= \$ref;


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Array Variables:Arrays contain a list of scalar data (singleelements). A list can hold an unlimited number ofelements. In Perl, arrays are defined with the at (@)symbol

@days = ("Monday", "Tuesday", "Wednesday"); or$days[0]=monday;

$days[1]=Tuesday;

my @magic_numbers = (23, 42, 69);my @random_scalars = ("mumble", 123.45, "willy thewombat", -300);


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Using qw// to populate arrays: If youre working with lists and arrays a lot, youmight find that it gets very tiresome to be typing so manyquotes and commas. Lets take fruit example:

my @fruits = ("apples", "oranges", "guavas", "mango","grapes");

We had to type the quotes character ten times, along with

four commas, and that was only for a short list. If your list islonger,then????we can use qwmy @fruits = qw/apples oranges guavas mango grapes/;


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Shift/unshift and push/pop functionsShift/unshift and push/pop functions shift() deletes the firstelement of the array and returns

that value

unshift() adds a new element or elements to thebeginningarray

pop() deletes the lastelement of the array and returnsthat value

push() adds an element or elements to the endof thearray


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Hash:Hashes are complex lists with both a key and a

value part for each element of the list. We define a hashusing the percent symbol (%).

special arrays with words as index.

Eg:%ages = ('Martin' => 28, 'Sharon' => 35,'Rikke' => 29,);

print "Rikke is $ages{Rikke} years old\n";


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#!/usr/bin/perl -w

# this is my first program

print "What is your name? ";$name = ;

chomp ($name);print "Hello, $name!\n";

Simple Example:


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Escaping Characters:

when you would like to print a dollar sign(specialcharacter) rather than use one to define a variable. To do

this you must "escape" the character using a backslash(\).some of the special char are: . , ; $ # @ \ / * ' < >Eg:$string = "David paid \$4.34 for Larry\'s shirt.";

$email = "youremail\@youremail.com";


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Assignment operators

a = a % ba %= b%=

a = a / ba /= b/=

a = a * ba *= b*=

a = a ba -= b-=

a = a + ba += b+=

a = ba = b=

Same asExampleOperator


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Logical operatorsLogical operators

Logical NOT!

Logical OR||

Logical AND&&

DoesOperator

These logical operators are very similar to those in C

Used with operands that have boolean values TRUE

and FALSE, or which can be converted to these values;typically 1 means TRUE and 0 means FALSE


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Logical operators examplesLogical operators examples$x = 1; $y = 0;

# example of AND$z = $x && $y;print "$x && $y = $z\n";

# prints 1 && 0 = 0

# example of OR$z = $x || $y;print "$x || $y = $z\n";# prints 1 || 0 = 1

# example of NOT$z = !$y;print "!$y = $z\n";# prints !0 = 1


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Numerical comparisonNumerical comparison

< = > returns -1, 0,or 1 if the left sideis less than, equalto, or greater than

the right side

Other operators re-turn TRUE if the

comparison is true,otherwise it will be

blank!Less than orequal?

=

Less than?Left-to-right comp< = >

Not equal?!=

Is equal?==ComparisonOperator


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String comparisonString comparison

Comparison/ActionOperator

get ASCII num of charord(char)

get char for ASCII numchr(num)

convert to lower caselc(string)

convert to upper caseuc(string)

repeatx

concatenation.

-1, 0, or 1, dependingcmp

less than?Lt

greater than?gt

not equal?ne

is equal?eq


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String comparison exampleString comparison example

$a = "hi";$b = "hello";

$equal = $a eq $b;print "$a eq $b = $equal\n";

$equal = $a ne $b;print "$a ne $b = $equal\n"; # $equal=1

$compare = $a cmp $b;

print "$a cmp $b = $compare\n"; #$compare=-1

$compare = $b cmp $a;print "$b cmp $a = $compare\n"; #$compare=1


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Operators Operation Performed

++,-- Auto Increment and Auto Decrement

-,~,! Operators with single operand

* * Exponentiation

=~,!~ Pattern matching operators

*,/,%,x Multiplication,Division,Remainder,RepetitionAddition, Subtraction, Concatenation+,-, .

Operator precedence


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Loops and conditions


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If the test expression is true, then execute thestatement(s) following

#!/usr/bin/perl$major = chemistry;

if ($major eq chemistry) {print Welcome, chemistry student!\n;

}if ($major ne chemistry) {

print Youre not a chemistry student.\n;print Why not?\n;}# note: need the curly braces

IF statementsIF statements


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Sometimes more convenient than just IF statements#!/usr/bin/perl$major = "chemistry";if ($major eq "chemistry"){print "Welcome, chemistry student!\n";

}else{print "You're not a chemistry student.\n";print "Why not?\n";}# note: need the curly braces

IF/ELSE statements


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useful in picking one possibility out of a list of several#!/usr/bin/perl$grade = "F";if ($grade eq "A") {

print "Excellent!\n";

}elsif ($grade eq "B") {print "Good work.\n";

}elsif ($grade eq "C") {

print "Needs improvement.\n";}else {

print "I suggest you start coming to office hours.\n";}

ELSIF statements


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While loops test one expression for truth, and will keep runningthe loop as long as the expression returns true. While loops aregood for iterating over arrays or through lines in a file.

Eg: copy a file content into another file.

open(pat,output.txt);$temp=;

while($temp){

print out $temp;$temp=;;

}

File Name File Handler Permission

pat readout write

datalog.txtoutput.txt

condition(It executeup to end of the file).

While


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For StatementLoop (repeatedly execute a statement block) until a given

condition is met

Syntax:for (initializer, test, increment/decrement){statement block}

Eg: find sum of 10 no's$sum=0;

for($i=1;$i


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Foreach StatementThe foreach loop takes each element of the array and

uses it with your code.

Eg:

@name = ("Rose","Shan","Mani","Karthi");foreach $x (@name){print "$x\n";}

Output:RoseShanManiKarthi

First time of execution it assign

$x=Rose

second iteration it assign x=Shan

iteration going on till end of the array

Firstelement

of array


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NEXT statementNEXT statement

Skip to next iteration of a loop Equivalent to Cs continue statement

for ($i=0; $i


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LAST statementLAST statement

Skip out of loop and exit it completely Equivalent to Cs break statement

for ($i=0; $i


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File Handling


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Opening a fileOpening a file

Before reading from or writing into the file weneed to open that file first.

To open a file call the library function open

The syntax for open library function isopen(filehandler, filename);

while calling open function, we need to supply

two arguments:

--> filehandler represents the name that the perlinterpreter uses to refer to the file

--> filename represents the name of the file you want to


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Chop( ) and chomp( ) operatorsChop( ) and chomp( ) operators

Chop() operatorused to remove the last character from the string

Eg: $a=hello;

print chop($a);#it prints hell by terminating the last character

Chomp() operator

Also similar to chop() but only removes thecharacter if it is a end-of-line character

Eg: $a=hello \n;

print chomp($a);


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File access modesFile access modes Read mode:

Enables the program to read the existingcontents of the file but does not enable it towrite into the file

Write mode:

Destroys the current content of the file and

overwrites them with the output supplied by theprogram

Append mode:

Appends output supplied by the program

to the existing contents of the file


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Reading a single line in a text fileReading a single line in a text file Use open and close functions Need a file handle to represent the file Use equality operator to read a line or an array of (all) lines

# Note: file random.txt must be in same directory, or else# must specify an absolute path

open(TXT, "


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Reading a whole fileReading a whole file

To get all the lines, simply assign toan array variable

open(TXT, "


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Writing to a text fileWriting to a text file

Use the > symbol in front of the filename to write,instead of < to read

open(TXT, ">written.txt"); # open the file forwriting

print TXT "hello, testing!\n"; # write a line

print TXT "end of test.\n"; # write another line

close(TXT); # close file again


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Appending to the text fileAppending to the text file

To append (add to the end of an existing file), usethe >> symbol before the filename instead of>

open(TXT, ">>written.txt"); # open the file for writing

print TXT "Add a line!\n"; # write an additional line

close(TXT); # close file again


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Detecting read/write errorsDetecting read/write errors

If a file operation has an error, it typically returns an errormessage to the $! variable This example previews subroutinesopen(FP, "


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DieDie

The die function is used in Perl to stop the interpreter in case of anerror and print a meaningful error message. A special variable in Perl $! Is always set to the error message of the

last requested operation of the system(such as disl i/o). Always used in a string context

Example:

open(MYFILE,


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Files in a directoryFiles in a directory

Can get all the files in a given directory using the opendir()function

opendir(CDIR, "."); # gives current directory@filenames = readdir(CDIR); # get all the filenames

@filenames = sort(@filenames); # sort them!closedir(CDIR);foreach $filename(@filenames){print "$filename\n";

}


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Split

split is used to split up the string and place it in an array

$info = "Caine:Michael:Actor:14, Leafy Drive";@personal = split(/:/, $info);

output: @personal = ("Caine", "Michael", "Actor", "14,Leafy Drive");

$_ = "Capes:Geoff::Shot putter:::Big Avenue";

@personal = split(/:+/);

Output: @personal = ("Capes", "Geoff","Shot putter", "BigAvenue");


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The join function takes a list of values and glues them togetherwith a glue string between each list element.

$bigstring = join($glue,$list); # The glue is not a regularexpression but just acharacter or strings

Eg:

@mylist = qw(mani shan ramesh);$outline =join(":",@mylist);print "$outline";

output:

mani:shan:ramesh

Join


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Exercises:

1. Create a text file and and write 10 numbers in single roweg: 12,32,43,23,etc

read numbers from this file and create new file with

numbers are in column wise using perl.

12,32,43,54,76,15,26,76

12324354761526

row.txt column.txt

S b i


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SubroutineSubroutine Subroutines are called using the name of the subroutine

preceded by an ampersand

&name

Eg:print "The start of the main body.\n";

&great_perl;print "The end of the main body.\n";sub great_perl{

print "From the subroutine; PERL is great!\n";

}# The start of the main body.# From the subroutine; PERL is great!# The end of the main body.

P i lPassing values


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Passing valuesPassing values

Values are passed to a subroutine using a specialunderscore array @_

Use $_[0], $_[1], etc, to access each element

&print_args("One", "Two", "Three");

sub print_args{

$i = 1;foreach $arg(@_){

print "Argument $i is $arg.\n";$i++;}

}

Output:Argument 1 is OneArgument 2 is TwoArgument 3 is Three

R lR l


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Return valuesReturn values

Subroutines can return values, like a function; in thisinstance, we do not use the & prefix

$x = 5;$y = square($x);

print "$x squared is $y\n";

sub square{return $_[0] * $_[0];

}

Output:5 squared is 25


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Regular expressionsRegular expressions Perl defines a special operators that test whether a

particular pattern appears in the character string

Pattern is a sequence of characters to be searched for ina character string out

Regular expression is used for,

Complex string comparisons


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=~ operator returns true if the pattern appears in the string

if $temp = Tessolve Services Pvt Ltd.,

then it returns True

$temp =~ /Tessolve/ PatternString

String Comparison


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Some of the Example String are,

1. I am working in tessolve2. Tessolve is in Bangalore3. Tessolve

Pattern True Examples

/tessolve/ 1,2,3 true/^tessolve/ 2,3 only true Begging of the string/tessolve$/ 1,3 only true End of the string

/^tessolve$/ 3 only true Exact word/tessolve/i 1,2 only true case sensitive


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Pattern Anchors


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Pattern Matching Strings11 34time11 5609847:34time

47 90timeTime 47:34Am 5Am45

/\d\d\s\d\d/;

/\d\d[\s\:]\d\d/

/\w\w[\s\d]\d/


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Eg:$string =~ m/^\S{1,8}\.\S{0,3}/;

Some match strings are,newfile.txtaa.mdi


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String Selections

We can select a string using Regular expression

( ) is used for grouping and to store variable.

Eg:$temp =~ /(\d\d)\-(\d\d)\-(\d\d)/;

$1 $2 $3

If $temp value is 24-01-10 then$1=24$2=01$3=10

S b tit ti


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Substitutions

Replace every "Bill Clinton" with an "Al Gore"$string =~ s/Bill Clinton/Al Gore/;

Now do it ignoring the case of bIlL ClInToN.$string =~ s/Bill Clinton/Al Gore/i;

Translations


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Translations

Change all vowels to upper case vowels:$string =~ tr/[a,e,i,o,u,y]/[A,E,I,O,U,Y]/;

Change everything to upper case:$string =~ tr/[a-z]/[A-Z]/;

Change everything to lower case$string =~ tr/[A-Z]/[a-z]/;

Change all vowels to numbers to avoid "4 letter words" in aserial number.$string =~ tr/[A,E,I,O,U,Y]/[1,2,3,4,5]/;


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Exercise2:

Extract file name and modification date from the below example.


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open("patt","


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Output:


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Write Excel


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Write excel perl module is not come along with default Perl IDE.

We need to install it. Installation procedure is,

1. Download Perl Write Excel module from the followingdownload path.http://search.cpan.org/CPAN/authors/id/J/JM/JMCNAMARA/Spre

2.Extract downloaded zip file.

3.copy Spreadsheet folder from the extracted file Spreadsheet-WriteExcel-2.37\lib

3.Paste Spreadsheet folder into the following path,c:\perl\site\lib\

CreateExcel package
http://search.cpan.org/CPAN/authors/id/J/JM/JMCNAMARA/Spreadsheet-WriteExcel-2.37.tar.gzhttp://search.cpan.org/CPAN/authors/id/J/JM/JMCNAMARA/Spreadsheet-WriteExcel-2.37.tar.gz


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use Spreadsheet::WriteExcel;

my $workbook = Spreadsheet::WriteExcel->new("example\.xls");

$worksheet{Sheet1} = $workbook->add_worksheet('Sheet1');

$worksheet{hello} = $workbook->add_worksheet('hello');$worksheet{Sheet1}->write(0 , 0 ,"new cell");

Createexample.xls

file

Excel package

Create new sheet withthe name hello inside

the example.xls file

Row Column


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For More information about Perl Write Excel visit this site:http://cpansearch.perl.org/src/JMCNAMARA/Spreadsheet-W
http://cpansearch.perl.org/src/JMCNAMARA/Spreadsheet-WriteExcel-0.37/WriteExcel/doc/WriteExcel.htmlhttp://cpansearch.perl.org/src/JMCNAMARA/Spreadsheet-WriteExcel-0.37/WriteExcel/doc/WriteExcel.html

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