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Perl ScriptingPerl Scripting

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Course ContentsCourse Contents

1. Introduction to Perl

2. Working with scalars (numbers & strings)

3. Operators and functions

4. Conditions & loops

5. Working with lists (arrays & hashes)

6. Sub-routines

7. Regular expressions

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Contd..Contd..

8. references and complex data structures

9. debugging in Perl

10. Packages & Modules

11. managing files and directories

12. working with files and I/O

13. handling databases in Perl

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1. Introduction to Perl1. Introduction to Perl

y Perl stands for Practical Extraction and

Report Language.

y Perl is a mixture of UNIX tools (sed, grep,

awk etc.), Shell Scripting, C and ObjectOriented features.

y Perl was created by Larry Wall. It is now not

owned by any single Organization. Perl isdefined and maintained by a group of

volunteer programmers including LarryWall.

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Features ofPerlFeatures ofPerl

1. Perl is free

2. Perl is both a compiled and interpretedlanguage

3. Perl is portable

4. Perl can interface with other languages

5. Perl is easy to use and debug

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How to get PerlHow to get Perl

Perl can be downloaded from the Internetthru www.perl.org (or) www.perl.com

The current version of Perl is 5.10.0.

Perl is available on different platforms,Unix,Windows, MacOS etc.

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Writing the first programWriting the first program

$ vi first.pl

# program to print a message

print Hello, World\n ;

To run the program,

$ perl first.pl

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About the ProgramAbout the Program

Any line that starts with a #, is a comment

To display messages, print command is used

Every perl statement must end with a ;

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Command Line OptionsCommand Line Options

To know the current version of Perl

$ perl v

To check the syntax errors only but does not

run the script

$ perl c first.pl

To turn on the warnings

$ perl w first.pl

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Data TypesData Types

Perl has two types of data:

1. scalars: data consisting of a single thing

ex: Numbers, Strings, References

2. lists: data consisting of a collection of

single things or scalars

ex:Arrays, Hashes

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2.Scalars2.Scalars

A) Numbers:

4 45e-4

3.2 0xbeef

.234567 0125. 1_234_456

10E2

Perl does not differentiate between integersand floats, signed or unsigned, or short andlong numbers. Perl converts between thenumber types as needed in our scripts

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ScalarsScalars

B) Strings :A string is zero or more characters

surrounded by single quotes ( )

or by double quotes ()

Escape sequences are used forstring formatting in print function.

\n new line

\t tab\b backspace

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ScalarsScalars

\a bell sound

\0nn octal

\0xnn hexadecimal

\l make next letter lower case

\u make next letter upper case

\L make all the following letters lower

\U make all the following letters upper

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ScalarsScalars

Converting between numbers and strings:Since, numbers and strings are scalar data,

they are interchangeable.

ex: 5 + 14 gives 19

foo + 5 gives 5

23abc + 7 gives 30

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Scalar VariablesScalar Variables

$a=5;$a=$b=5;$a=$b=5,$c=7;

$s=abc;$t=xyz;Rules for variable names:1.should start with a letter, underscore

2.case sensitive3.can be up to 255 characters.We dont have to declare or initialize variables in thebeginning.

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InputInput

Reading scalar values from Keyboard:

$a=;

chomp ($a);When we enter values from the keyboard,

\n

is automatically attached to the input value.To remove \n from the input, we use chomp

function.

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OutputOutput

Displaying the values on the screen:

print ($a\n);

printf (%.2f\n,$b);

$c=sprintf(%.2f,$b);

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3.Operators & Functions3.Operators & Functions

Arithmetic operators:

+ (addition),

- (subtraction),

* (multiplication),

/ (division),

% (remainder),

** (exponent)

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OperatorsOperators

Assignment Operators:

+=, -=,*=, /=, %=, **=

Increment and Decrement Operators:

++, --

Conditional Operator:

exp1?exp2:exp3

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OperatorsOperators

Bitwise Operators:

String catenation operator:

.

String repetition operator:

x

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OperatorsOperators

Quoting the strings:

Single quotes: q/how are you/

Double quotes: qq/how are you/

General quotes: qw (abc);

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NumberFunctionsNumberFunctions

abs () absolute value

int () converts to integer

sin () sine value

cos () cosine value

rand () random number

exp () e to the power of

atan2 () arctangentord () ascii number

sqrt () square root

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String FunctionsString Functions

chr () ascii characterindex () returns the pos. of chr.length () length

reverse () reverses a scalarrindex () reverse indexsubstr () substringlc () lowercaseconversionuc () upper caseconversionlcfirst () first character loweruc first() first character upper

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4.Conditions and Loops4.Conditions and Loops

if

if (condition) { statements}

if (condition)

{statements}

else

{statements}

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Conditions and LoopsConditions and Loops

if (condition)

{

statements

}

elsif (condition)

{

statements}

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unless

unless (condition)

{statements

}

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while

while (condition)

{statements

}

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until

until (condition)

{statements

}

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do

do {statements}

while (condition);

do {statements}

until (condition);

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for

for (init; test; change){

statements

}

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foreach

foreach value (list){

statements

}

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Infinite loopswhile ()

{

statements}

for (;;)

{statements

}

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break from a control statement

lastcontinue

next

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$_ variable

It is the default placeholder for scalar

valuesexample

foreach (`dir`)

{print ($_\n);

}

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switchuse Switch;

switch ($value){

case 1 {print 1; }.

else {print 0 ;}}

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5.Arrays andHashes5.Arrays andHashes

CreatingArrays:

@nums = (1,2,3,4);

@nums = (1..4);@strings = (ab , cd , ef );

@strings = (a ,z);

@strings = ();

@combine=(@nums, @strings);

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Arrays andHashesArrays andHashes

Printing theArray:

print (@nums\n);

print (@strings\n);

print (@combine\n);Processing each element:

foreach $x (@nums)

{print ($x\n);

}

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AccessingArray elements:

$nums[3];

The subscript starts from 0 to n-1NegativeArray Indexes:

$nums[-1];

Negative array subscripts will countback

from the end of the array.

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GrowingArrays:@nums=(1..4);

$nums[6]=7;

Result is 1,2,3,4,undefined, undefined,7

Finding the end of theArray:

$end=$#nums;

Finding the length of theArray:

$len=@nums;

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Sorting theArray:

cmp (strings), < = > (numbers)

@sorted=sort {$a cmp $b} @strings;@sorted=sort {$a < = > $b} @nums;

Reversing theArray:

@new=reverse (@old);

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push and pop functions allow you toadd or remove elements from the end

of the list

$new=push (@nums,5);

$new1=pop (@nums);

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slice creates pieces of the Array@array=(1..10);@slice=@array[0,1,2];

splitting the data into anArray$strings=12 23 43;@nums=split( ,$strings);

joining the data from anArray$strings=join(+, @nums);

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Creating a Hash:%hash=(key=>value, key=>value, key=>value);Ex:

%pairs=(red=>255, blue=>355, green=>455);Accessing Hash Elements:

$hash {$key};Ex: $pairs {red};

Printing the Hash:print %hash;

Ex: print %pairs;

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Processing a Hash:foreach $key (sort keys %hash){

print $hash {$key}\n;}while (($key, $value) = each (%hash){

print $hash {$key} \n;}

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Ex:

foreach $key (sort keys %pairs)

{

print $pairs {$key}\n;}

or

while (($key,$value) = each (%pairs))

{print $pairs {$key} \n;

}

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Adding an element to a Hash:

$hash {$key} = $value;

Ex:

$pairs {yellow}=555;

Deleting an element from a Hash:

delete ($hash {

$key});Ex:

delete ($pairs {red});

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Inverting a Hash:

%new=reverse %hash;

Ex:

%newpairs = reverse %pairs;

Finding the no. of keys in a Hash:

$n=keys %hash;

Ex:

$n=keys %pairs;

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6.Subroutines6.Subroutines

The terms function and subroutine areentirely equivalent in Perl.

Perl handles three types of functions.

1. Built-in: These are the functions that are

defined by the standard Perl library that we

can use any where in our Perl scripts.

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SubroutinesSubroutines

2. Additional: These are the functions that areavailable to us by using the additional Perlmodules or libraries, written by other Perl

programmers, that we can load in at the startof the script.

3. Subroutines: These are user definedfunctions. By convention, the term subroutine

is used to identify the function as user definedone.

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Defining & Calling basic subroutines:print enter temperature in forenheight \n;

chomp ($f=);

&cal();print The result is $cel\n;

sub cal ()

{

$cel=($f-32)*5/9;

}

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Returning values from a subroutine:$sum=&cal();print The sum is $sum\n;

sub cal (){

print enter two nos. \n;chomp ($n1=);

chomp ($n2=);return ($n1 + $n2);

}

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Using local variables inside a subroutine:We can create local variables inside a

subroutine usingmy modifier.

$sum=&cal();print The sum is $sum\n;sub cal (){

my ($n1,$n2);print enter two nos. \n;chomp ($n1=);chomp ($n2=);

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PassingArguments to a subroutine:$sum=&cal(3,5);print The sum is $sum\n;sub cal (){ my ($m,$n)= @_;

my $p=1;while ($n>0){ $p=$p*$m;

$n--;}

return ($p);}

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Anonymous subroutines:These are subroutines without namesand they operate sort of like pointers

to functions in C.

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7.REGULAR EXPRESSIONS7.REGULAR EXPRESSIONS

REGULAR EXPRESSION OPERATORS:

m//, s///, tr///

@x = grep /x/, @words;

PATTERN MATCHING OPERATORS:

=~, !~

REs:

abc exact character sequence

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REGULAR EXPRESSIONSREGULAR EXPRESSIONS

^abc abc at the beginning

abc$ abc at the ending

a|b a or b

ab {2,4}c a followed by 2,3,4 bs

followed by c

ab{2,}c a followed by at least 2 bs

followed by c

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ab*c a followed by zero or more

bs followed by c

ab+c a followed by one or more

bs followed by cab?c a followed by optional b

followed by c (abc or ac)

a.c an a followed by any singlecharacter (no newline) followed by c

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a\.c a.c exactly

[abc] any one of a , b or c

[Aa]bc Abc or abc

[^abc] not containing a or b or c

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8.References8.References

A reference is similar to a pointer in C.The reference itself is a scalar, it can be

assigned to a scalar variable, printed, added

to, passed to subroutine etc. To find outwhat the reference points to, we can

dereference the reference.

Creating a reference for a scalar:

$str=This is a string;

$strref=\$str;

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ReferencesReferences

Dereferencing a scalar reference:$originalstr=$$strref;Creating a reference for anArray:

@array=(1..10);$arrayref=\@array;Dereferencing an array reference:@originalarray=@$arrayref;

To refer to individual elements:$originalarray[0] or $$arrayref[0];

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Creating a reference for a hash:

%hash=(a=>255,b=>355,c=>455);

$hashref=\%hash;

Dereferencing a hash reference:

%originalhash=%$hashref;

To refer to individual keys:

$originalhash{a} or $$hashref{a};

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Creating a reference for a subroutine:$subref=\&mysub;Dereferencing a subroutine:

$result=&$subref(3,5);Creating anonymous subroutines:$subref=sub {.};

Dereferencing a subroutine:$result=&$subref();

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Anonymous data: The term anonymous meanswithout a name.Anonymous data refers to data(usually arrays, hashes and subroutines) that wecan only access through a reference i.e. the datadoes not have an associated variable name. Usinganonymous data, we can create nested datastructures such as,

1.Arrays ofArrays2. Hashes ofArrays

3. Hashes of Hashes

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Arrays ofArrays:

@array= ( [0,1,2],

[23,33,43],

[53,54,55]

);

Referring to individual elements:

$array[0][1] or $array[0]->[1]

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Hashes ofArrays:

%hash= ( b=>[0,1,2],

g=> [23,33,43],

r=>[53,54,55]

);


$hash{b}[1] or $array{b}->[1]

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Hashes of Hashes:

%hash=(a=>{x=>0,y=>1,z=>2},

b=>{l=>3,m=>4,n=>5},

c=>{p=>53,q=>54,r=>55}

);


$hash{a}{x} or $array{a}->{x}

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9.Debugging in Perl9.Debugging in Perl

Perl comes with a source level debugger.The debugger can help us track downsubtle problems in our code.

We shall see,

1. how to start and run the debugger

2. step through the execution of the script3. trace the execution of the script

4. list the source in various ways

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Debugging in PerlDebugging in Perl

5. print out the values of the variables6. set the breakpoints

To invoke the debugger,$ perl d temp.plAfter the display of some messages, we seemain::(temp.pl:1): system (cls);

DB

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DB debugger prompt with

command number

main package nametemp.pl script name

1 line no. of the script

system (cls) line in the script to be run

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Debugger Commands:

n runs a line of the script, silently

executes subroutines

s runs a line of the script, steps intosubroutines

l list 10 lines after the current line

- list the lines before the currentline

x prints the value of any scalar, list

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Debugger Commands:

X print out all the variables in the

current package

V same as X except it takes anoptional name of a package

r stops stepping thru the subroutine,

executes rest of it, returns to thecalling place.

c runs the script without stepping thru

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Debugger Commands:

b to set a break point

S prints all the available subroutines

t turns tracing on or off

h help

|h pause help with breaks

!3 refers to the command no. 3

H -3 lists last 3 commands

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Debugger Commands:

T show the stack trace

w shows a window around the

current line

L lists all break points

d deletes a break point

D deletes all set break points

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10.PACKAGES & MODULES10.PACKAGES & MODULES

What is a Package?A package is a namespace It is a space thatprovides its own global scope for identifiers. Itfunctions as a private programming space.

How to create Packages?

We can place the code for a Package in itsown file, or in multiple files, or even createseveral packages in the same file. To switchinto another package, we use the packagestatement.

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PACKAGES & MODULESPACKAGES & MODULES

$ vi packages.plpackage package1;BEGIN {}

$x=1;sub subroutine1 { print one\n ;}return 1;

END {}

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$ vi prg1.plrequire packages.pl;

package1::subroutine1();

print $package1::x;To run,

$ perl prg1.pl

To know in which package we are,print __PACKAGE__;

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Splitting a Package across files:

$ vi file1.pl

package package1;BEGIN {}sub sub1 { print hello\n; }return 1;

END {}

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$ vi file2.pl

package package1;

BEGIN {}sub sub2 { print bye\n; }

return 1;

END {}

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$ vi original.plrequire file1.pl;

require file2.pl;

package1::sub1();package1::sub2();

The result is,

hellobye

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Our Declaration: Our declaration sets globalscope across packages, i.e. variable of one

package can be accessed in another package.

$ vi packages.plpackage package1;

our $data=1;

sub sub1 { print hello\n; }return 1

END {}

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package package2;

sub sub2 { print $data\n; }

return 1;

END {}

To run this,

package1::sub1();

package2::sub2();

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Creating Modules: A Perl Module is just apackage in which the package is defined in a

file with the same name as the package and

has the extension pm.

This allows subroutine names automatically

exported to the code when we include a

Module.

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$ vi Module1.pmpackage Module1;BEGIN

{ use Exporter();@ISA=qw (Exporter);@EXPORT=qw (&subroutine1&subroutine2);

}sub subroutine1 { print hello\n ;}sub subroutine2 { print thanks\n; }return 1;

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$ vi final.pluse Module1;

subroutine1();

subroutine2();$ perl final.pl;

CPAN:There are literally hundreds of

modules that have been developed foruse

with Perl.

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Many are available with the Perl Distributionitself. CPAN (Comprehensive Perl Archive

Network) serves as a repository for user

developed modules. An up-to-date survey of

the contents of CPAN can be found at

www.perl.com

However, there are two drawbacks to the

CPAN modules. The first is that we have todownload, build and install modules before

they can be used. Some modules may require

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compilation which means that we need aworking C compiler.

Secondly, most of the CPAN modules are

developed for UNIX Perl. For installingWindows specific modules, there is a special

tool called ppm.

C:\> ppm

PRAGMAS:These are the modules that

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provide instructions for Perl to behave at bothcompile time and run time.

ex:

subs:allows you to pre-declare subroutine names.

vars:

allows you to pre-declare global variables sothat they can be accepted under strict

pragma.

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strict:disallows bare words, global variablesand symbolic references.

integer:

allows only integer arithmetic.

constant:

allows to create constant variables atcompile time.

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Global variable: Any variable that is notexplicitly declared with my or local,automatically becomes a global variable

and is available at any point in that script.Any variable declared in a block with my

or local becomes a local variable to that

block.Difference between my and local:

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A my variable is only available to the code upuntil the nearest enclosing block or subroutinedefinition. If we call another subroutine withinthat one, the second subroutine will not have

access to those variables. Local variablesdeclared with local are available to the codeinside that block and subroutine and to thenested subroutines called from the same

subroutine.

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MANAGING FILES & DIRECTORIESMANAGING FILES & DIRECTORIES

Removing files & links:unlink temp, config, foo;

Other file commands:

chmod changing the file permissionschown changing the owner of the file

fileno returns the file descriptor

utime changes the time stamp

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Directory Commands:chdir:chdir images;use Cwd;$curr=cwd();print $curr\n;

File Listing (File Globbing):@files=;while () {

print $_ ,\n;

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Directory Commands:mkdir:

mkdir temp, 0777;

rmdir:

rmdir temp;

Perl and the Environment: Perlenvironment variables are stored in aspecial hash called %ENV.

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Environment Variables are commonly inupper case.

To view all the EnvironmentVariables,

foreach $key (keys %ENV)

{

print $key -> $ENV {$key} \n;

}

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To run OS commands,system (ls);

$ls=`ls`;

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WORKINGWITHFILES & I/OWORKINGWITHFILES & I/O

Creating a file:open (FH,>myfile) or die can not create\n;

Reading a file:

while ()

{

.

}

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Writing to a file:print FH $input\n;

Closing a file:

close FH;open options:

> writing

< reading+> read and write

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File Tests:-d directory ?

-e file exists ?

-f plain file ?-l symbolic link ?

-r readable ?

-s ? Big is the file ?-w writable ?

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File Tests:-x executable ?

-z empty file ?

-B binary file ?-T text file ?

Command line arguments:

Command line arguments are stored in aspecial list @ARGV.

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foreach $arg (@ARGV) {print $arg \n;

}

Use the DBI Module

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#!/usr/local/bin/perl

use DBI;

Use the DBI Module

Establish connection and get a handle to it

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use DBI;

$db_handle = DBI->connect(DBI:mysql:sanskar_club:sql.njit.edu,

sanskar, pswd) || die (Couldnt connect\n);

Syntax ofDBI->connect()

DBI->connect(data_source, username, password);

data_source will be DBI:driver_name:driver_parameters

For MYSQL at NJIT

driver_name = mysqldriver_parameters = database_username:sql.njit.eduusername = ucid/club account namepassword = afs password

Establish connection and get a handle to it

Prepare an SQL query

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use DBI;



$stmt_handle = $db_handle->prepare("SELECT name, email, numpeople,accomdetails FROM user_detail");

Prepare an SQL query

Execute the SQL query

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use DBI;



$stmt_handle = $db_handle->prepare("SELECT name, email, numpeople,

accomdetails FROM user_detail");

$stmt_handle ->execute;

Execute the SQL query

Finish with statement handle

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use DBI;



$stmt_handle = $db_handle->prepare("SELECT name, email, numpeople,accomdetails FROM user_detail");

$stmt_handle ->execute;while (@row = $stmt_handle->fetchrow()) {

foreach $field (@row){

print "$field ";}print \n;

}

$stmt_handle->finish();

Finish withstatement handle

Close the connection

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use DBI;


sanskar,pswd) || die (Couldnt connect\n);

$stmt_handle = $db_handle->prepare("SELECT name,email,numpeople,

accomdetails FROM user_detail");$stmt_handle ->execute;

Close the connection

Contd

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while (@row = $stmt_handle->fetchrow()) {

foreach $field (@row){

print "$field ";

}

print \n;}

$stmt_handle->finish();

$db_handle->disconnect();

Contd..

38875080 Perl Scripting

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Transcript of 38875080 Perl Scripting