Ashish Kumar Jha Brief Perl Tutorial

7/31/2019 Ashish Kumar Jha Brief Perl Tutorial

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Agenda

Perl Basics Data Types Operators Control Structures

Lists Hashes Sub Routines


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Practical Extraction & Reporting Language Perl is a High-level Scripting language Faster than sh or csh, slower than C More powerful than C, and easier to use No need for sed, awk, head, wc, tr, Compiles at run-time Available for Unix, Linux, Mac etc. Best Regular Expressions on Earth

What is Perl?


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Whats Perl Good For?

Quick scripts, complex scripts Parsing & restructuring data files CGI-BIN scripts High-level programming

o Networking librarieso Graphics librarieso Database interface libraries


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Whats Perl Bad For?

Compute-intensive applications (use C) Hardware interfacing (device drivers)


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Installation for Unix / Windows

Unix Windows


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Perl Basics

Leading spaces on a line are ignored Statements are terminated with a semicolon. Anything after a hash sign (#) is ignored

except in strings. A string is basically a series of characters

enclosed in quotes Spaces, tabs, and blank lines outside of

strings are irrelevant-one space is as good asa hundred.


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File Naming Schemeo filename.pl (programs)o filename.pm (modules collection of useful perlsubroutines)

o filename.ph (old Perl 4 header file)

Should call exit() function whenfinishedo Exit value of zero means success

exit (0); # successfulo Exit value non-zero means failure exit (2); # failure

Perl Basics


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Invoking perl from cmd-line

o perl -w (-w to give all warnings)o print hello world \n;o __END__

Output : hello world

Perl Helpo man perlo perldoc perlfunc (perl built-in functions)


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Data Types

Integer literalo 25 750000 1_000_000_000o 8#100 16#FFFF0000

Floating Point literalo 1.25 50.0 6.02e23 -1.6E-8

String literalo hi therehi there,$nameo print Text Utility, version $ver\n;o Use double quote for special charinterpretation


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Data Types

Booleano 0 0.0 represents False o all other values represents True


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Numericand String Literals

Numbers - This is the most basic data type. Strings - A string is a series of characters

that are handled as one unit.Arrays - An array is a series of numbers and

strings handled as a unit.Associative Arrays - This is the most

complicated data type.


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Special Esc Sequence chars

\n,\r, \t, \a, \b, \x are also availableo \l Lowercase next lettero \L Lowercase all following letters until \Eo \u Uppercase next lettero \U Uppercase all following until \E

o \Q Backslash-quote all nonalphanumerics until\Eo \E Terminate \L , \U, or \Q


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Operators

Math(operator prcedeces are as in C)o The usual suspects: + - * /

$total = $subtotal * (1 + $tax / 100.0);

o Exponentiation: ** $cube = $value ** 3;$cuberoot = $value ** (1.0/3);

o Bit-level Operations left-shift: $val = $bits >> 8;


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Operators

Assignmentso As usual: = += -= *= /= **= =

$value *= 5; $longword


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Operators

Boolean (against bits in each byte)o Usual operators: & |o Exclusive-or: ^o Bitwise Negation: ~

$picture = $backgnd & ~$mask | $image;

Boolean Assignmento &= |= ^=

$picture &= $mask;


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Operators

Logical (expressions)o && And operatoro | | Or operatoro ! Not operatoro AND And, low precedenceo OR Or, low precedenceo NOT Not, low precedenceo XOR Exclusive or, low precedence


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Operators

o Short Circuit Operators expr1 && expr2

expr1 is evaluated. expr2 is only evaluated if expr1 was true.

expr1 || expr2

expr1 is evaluated. expr2 is only evaluated if expr1 was false.

Examples open () || die couldnt open file; $debug && print users name is $name\n;


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Operators

Modulo: %o $a = 123 % 10; ($a is 3)

Multiplier: xo print ride on the , choo-x2, train;(prints ride on the choo-choo-train)

o $stars = * x 80;

Assignment: %= x=


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Operators

String Concatenation: . .=o $name = Uncle . $space . Sam;o $cost = 34.99;

o $price = Hope Diamond, now only \$;o $price .= $cost;

String Repetition Operator xo "fred" x 3 # is "fredfredfred"


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Conditionals Operators

numeric string Equal: == eq Not Equal != ne Less/Greater Than: < > lt gt Less/Greater or equal: = le ge Zero and empty-string means False All other values equate to True


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numeric string Comparison: cmp

o Results in a value of -1, 0, or 1 Logical Not: !

Grouping: ( )

Conditionals Operators


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Scalar Variables

Scalaro $num = 14;o $fullname = Cass A. Nova;o Variable Names are Case Sensitiveo Variable name length is limited to 255

charso Underlines Allowed: $Program_Version =1.0;


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chop and chomp functions

chop function (any last char in the string isremoved)o $x = "hello world";o chop($x); # $x is now "hello worl"

chomp function (only newline char removed)o $a = "hello world\n";o chomp ($a); # $a is now "hello world"o chomp ($a); # aha! no change in $ao @stuff = ("hello\n","world\n","happy days");o chomp(@stuff); # @stuff is now ("hello","world","happy

days")


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Reading values from keyboard

o $a = ; # get the texto chomp($a); # get rid of that pesky newlineo A common abbreviation for these two lines is:

o chomp($a = );o @a = ; # read standard input in a listcontext


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undef value

What happens if you use a scalar variablebefore you give it a value?

Nothing serious, and definitely nothingfatal

Variables have the undef value before they

are first assigned This value looks like a zero when used as anumber, or the zero-length empty string whenused as a string


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Control Structures

if statement - first styleo if ($porridge_temp < 40) {print too hot.\n;}elsif ($porridge_temp > 150) {

print too cold.\n;}else {print just right\n;}


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Control Structures

if statement - second styleo statement if condition;

print \$index is $index if $DEBUG;

o Single statements onlyo Simple expressions only

unless is a reverse ifo statement unless condition;

print millenium is here! unless $year < 2000;


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Control Structures

for loop - first styleo for (initial; condition; increment) { code }

for ($i=0; $i


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Control Structures

for loop with default loop variable for (@employees) {print $_ is an employee\n;print; # this prints $_}

Foreach and For are actually the same.


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while

loopo while (condition) { code }

$cars = 7;while ($cars > 0) {print cars left: , $cars--, \n;}

while ($game_not_over) {}

Control Structures


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until loop is opposite of whileo until (condition) { code }

$cars = 7;until ($cars


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Bottom-check Loopso do { code } while (condition);o do { code } until (condition);

$value = 0;do {

printEnter Value:

;$value = ;

} until ($value > 0);

Control Structures


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Loop Controlso next operator - go on to next iterationo redo operator - re-runs current iterationo last operator - ends the loop immediately

o while (cond) {next if $a < 5;}

o You can break out of multilevel loops usinglabels (not covered in this presentation)

Control Structures


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o Break out of multilevel loops using labels top: while (condition) {for ($car in @cars) {do stuffnext top if situation;}}

Control Structures


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Loop Controls Exampleo while ($qty = &get_quantities) {last if $qty < 0; # denotes the endnext if $qty % 2; # skip evenquantities

$total += $qty;$qtycnt++;}print Average of Odd Quantities: ,$total/$qtycnt, \n;

Control Structures

N S i h S ?!?


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No Switch Statement?!?

Perl needs no Switch (Case) statement. Use if/else combinations instead

o if (cond1) { }elsif (cond2) { }elsifelse

This will be optimized at compile time

Li V i bl


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List Variables

List (one-dimensional array) A list is ordered scalar data The smallest array has no elements, while thelargest array can fill all of availablememory

List literalo (1,2,3) # array of three values 1, 2, and 3o ("fred",4.5) # two values, "fred" and 4.5

Li V i bl


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List Variables

o List constructor operator (1 .. 5) # same as (1, 2, 3, 4, 5) (1.2 .. 5.2) # same as (1.2, 2.2, 3.2, 4.2, 5.2)

o @memory = (16, 32, 48, 64);o @people = (Alice, Alex, Albert);o First element numbered 0 (can be changed)

o Single elements are scalar: $names[0] = Ferd;o Slices are ranges of elements @guys = @people[1..2];

o How big is my list? print Number of people: $#people\n;

Li t V i bl


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List Variables

List with lots of wordso @a = ("fred","barney","betty","wilma");o Alternative

@a = qw(fred barney betty wilma); # better! qw quoted words

Printing the whole listo print("The answer is ",@a,"\n");

Converting into scalaro ($a,$b,$c) = (1,2,3);o ($a,$b) = ($b,$a); # swap $a and $b

Li t V i bl


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List Variables

Removing an element in listo ($e,@fred) = @fred; # remove first element of @fred

Getting first elemento ($a) = @fred; # $a gets first element

As an array element access

o @fred = (7,8,9);o $b= $fred[0];#give7to$b(firstelementof @fred)o $fred[0] = 5; # now @fred = (5,8,9)o $fred[2]++;# increment third element of @fred

List Variables


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List Variables

Sliceso @fred[0,1]; # same as ($fred[0],$fred[1])o @who = (qw(fred barney betty wilma))[2,3];

Assigning values beyond array subsrcipto @fred = (1,2,3);o $fred[3] = "hi"; # @fred is now (1,2,3,"hi")o $fred[6] = "ho";

# @fred is (1,2,3,"hi",undef,undef,"ho")

o Use $#fred to get the index value of the lastelement of @fred

o A -ve subscript on an array counts back fromend

Push and Pop functions


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Push and Pop functions

The push and pop functions do things to the"right" side of a listo push(@mylist,$newvalue); # like @mylist =(@mylist,$newvalue) first argument must be an array variable name

o @mylist = (1,2,3);

o push(@mylist,4,5,6); # @mylist =(1,2,3,4,5,6)

o $oldvalue = pop(@mylist); # removes thelast element of @mylist The pop function returns undef if given an empty list

Shift and unshift functions


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Shift and unshift functions

unshift and shift functions perform the corresponding actions

on the "left" side of a listo unshift(@fred,$a); # like @fred = ($a,@fred);o unshift(@fred,$a,$b,$c); # like @fred = ($a,$b,$c,@fred);o $x = shift(@fred); # like ($x,@fred) = @fred;o shift returns undef if given an empty array variableo @fred = (5,6,7);

o unshift(@fred,2,3,4); # @fred is now (2,3,4,5,6,7)o $x = shift(@fred); # $x gets 2, @fred is now (3,4,5,6,7)

Reverse and Sort functions


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Reverse and Sort functions

reverse functiono @a = (7,8,9);o @b = reverse(@a); # gives @b the value of (9,8,7)o @b = reverse(7,8,9); # same thing

Sort functiono @x = sort("small","medium","large");o # @x gets "large","medium","small"o @y = (1,2,4,8,16,32,64);o @y = sort(@y); # @y gets 1,16,2,32,4,64,8

Hash Variables


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Hash Variables

Hash (associative array) Hash is like an array whose index values areany arbitrary scalars

The elements of a hash have no particular order A hash variable name is a percent sign (%)

followed by a letter, followed by zero or moreletters, digits, and underscores

Hash Variables


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Hash Variables

o $fred{"aaa"} = "bbb"; # creates key "aaa", value "bbb"o $fred{234.5} = 456.7; # creates key "234.5", value 456.7o %var = { name => paul, age => 33 };o Single elements are scalar

print $var{name}; $var{age}++;

o How many elements are in my hash? @allkeys = keys(%var); $num = $#allkeys;

Hash Variables


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Hash Variables

The keys functiono yields a list of all the current keys in the hash

$fred{"aaa"} = "bbb"; $fred{234.5} = 456.7; @list = keys(%fred); # @list gets ("aaa",234.5) or # (234.5,"aaa")

foreach $key (keys (%fred)) { # once for each key of %fred

print "at $key we have $fred{$key}\n"; # show key and value

}


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Hash Variables


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The value functiono The values(%hashname) function returns a list of allthe current values of the %hashname %lastname = (); # force %lastname empty $lastname{"fred"} = "flintstone"; $lastname{"barney"} = "rubble"; @lastnames = values(%lastname); # grab the values At this point @lastnames contains either ("flintstone", "rubble")or ("rubble", "flintstone").

Hash Variables

Hash Variables


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Hash Variables

The each functiono On each evaluation of this function for the same hash,the next successive key-value pair is returned untilall the elements have been accessed

o Step thru each key value pairs

while (($first,$last) = each(%lastname)) { print "The last name of $first is $last\n"; }


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Subroutines (Functions)


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Passing Argumentso Passes the valueo Lists are expanded

@a = (5,10,15);@b = (20,25);

&mysub(@a,@b); this passes five arguments: 5,10,15,20,25 mysub can receive them as 5 scalars, or one array

Subroutines (Functions)


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Noteso Recursion is legalo local is the Perl 4 version of my


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Special Variables


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$0 name of the program running $/ input record separator (\n) $\ output record separator (none) $, output field separator for print(none) $ Array Elements separator $. input line number

Special Variables


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$[ first element index number (0) $! system error message (related to $ERRNOvariable)

$$ Perl Process ID $^O Operating Systems name

Special Variables


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@_ list of all the arguments @INC library directories (require, use) @ARGV command line args list %ENV Environment variables

File Functions


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Much faster than system()o unlink file; - deletes a fileo rename oldfile, newfile;o rmdir directory;o link existingfile, newfile;

o symlink existingfile, newfile;o chmod 0644, file1, file2, ;o chown $uid, $gid, @filelist;


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Basic File I/O


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How does work?o opens each ARGV filename forreading

o if no ARGVs, reads from stdino great for writing filters, heres

cat: while () {print; # same as print $_;}

Basic File I/O


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Reading from a Pipeo open (FILEHANDLE, ps aux |) || die\ launch of ps failed: $!;while () {chop;print $_\n;}close FILEHANDLE;


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Pattern Matching


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A pattern is a sequence ofcharacters to be searched for ina character string

o syntax:string

=~pattern

o Returns true if it matches, falseif not.

o Example: match abc anywhere instring: if ($str =~ /abc/) { }


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Pattern Matching


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\b and \B Word boundary pattern Anchors /d[^eE]f/ Exclude Character [] Character-Range Escape Sequences \d Any digit [0-9] \D Anything other than a digit [^0-9] \w Any word character [_0-9a-zA-Z] \W Anything not a word character [^_0-9a-zA-Z] \s White space [ \r\t\n\f] \S Anything other than white space [^ \r\t\n\f]


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Substitution Operator


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Syntax : s/pattern/replacement/ $name =~ s/ASU/Arizona State University/; s/abc// s/[abc]+/0/

Options for the SubstitutionOperator


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p

g Change all occurrences of the pattern i Ignore case in pattern e Evaluate replacement string as expression m Treat string to be matched as multiple

lines o Evaluate only once s Treat string to be matched as single line x Ignore white space in pattern


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Perl versus Unix Utilities


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sed - substitutionso sed: s/xxx/yyy/go vi: :%s/xxx/yyy/go perl: s/xxx/yyy/g;

tr - translationso tr: tr [A-Z][a-z](platformdependent)

o perl: tr/A-Z/a-z/; (platformindependent)

Perl versus Unix Utilities


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wc - char / word / line countingo wc: wc -l < filenameo perl: perl -ne END{print $.\n} "value1",..}; $anon_hash_copy = { %hash};

To dereference a hash reference: %hash= %$href; $value = $href->{$key};

@slice=@$href{$key1,$key2}#no arrow!@keys = keys %$href;


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References to Functions


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To get a code reference: $cref =\&func;$cref = sub { ... }; To call a code reference:@returned = $cref->(@arguments);

@returned = &$cref(@arguments);


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Packages


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Collect data & functions in a separate(private) namespace

Similar to static functions & data in C Perl 4 concept, works in Perl 5 too Reusable code

require or use


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The require or use statements both pulla module into your program Require loads modules at runtime,useloads modules at compile-time

The required file extension for a Perl

module is ".pm". use NET::SSH;

Packages


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To find the current package:$this_pack = __PACKAGE__; To find the caller's package:$that_pack = caller();

Automating Module Clean-Up


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For set-up code, put executable statements outside

subroutine definitions in the module file For clean-up code, use an END subroutine in that

module. END { logmsg("shutdown");close(LF) or die "close

$Logfile failed: $!";}

Preparing a Module for Distribution


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Use h2xs -XA -n Command to generate ownmodules

Use the make dist directive to bundleit all up into a tar archive for easy

distribution.


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Reporting Errors and Warnings Like Built-Ins


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To print the errors that are there inour modules .

Use Carp ;

Building and Installing a CPAN Module


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% gunzip Some-Module-4.54.tar.gz% tar xf Some-Module-4.54% cd Some-Module-4.54% perl Makefile.PL% make

% make test% make install

Characteristics of OOP

Data encapsulation concept Reusability

ddi f di h i


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Extensibility:adding new features or responding to changing

operating environments can be solved by introducing a fewnew objects and modifying some existing ones;

Maintainability: objects can be maintained separately,making locating and fixing problems easier;

OOPS in PERL A class is a Perl package. This package for a classprovides the methods for objects.

Amethodis simply a Perl subroutine. The only catch withwriting such methods is that the name of the class is thefirst argument


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first argument.

An object in Perl is simply a reference to some data itemwithin the class. Perl provides abless() function which is used to return a

reference and which becomes an object.

OOPS in PERL Defining a Class :package Person; To create an object we need an object constructor . The object reference is created by blessing a reference to

the package's class .


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the package s class .

sub new{my $class = shift;my $self = {};bless $self, $class;return $self;}

OOPS in PERL

E d fi th d i


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Even we can define our own methods inPERL .

sub getFirstName {return $self->{_firstName};}

Inheritance in PERL

Acquiring the properties of one class


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Acquiring the properties of one classto another class .

Use @ISA for implementing inheritancein perl .

Searching for a method is in the order:

@ISA array , AUTOLOAD subroutine

AUTOLOAD subroutine


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Debugging in Perl

Debug mode: perl -d filename [args]


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Debug mode: perl d filename [args]o Display Commands

h Extended help h h Abbreviated help

l (lowercase-L) list lines of code l sub list subroutine sub l 5 list line 5 l 3-6 list lines 3 through 6 inclusive l list next window of lines

Debugging in Perl

o Display Commands (continued)


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w watch point /pat search forwards for patternpat(regular expressions legal)

?pat search backwards for patternpat(regular expressions legal)

S list all subroutines w/ packages

Debugging in Perl



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p y ( )

- (hyphen) list previous window p exprprints Perl expression expr = aliasvalue set a command alias H [-num] history (list previous cmds) commandexecute any Perl commandor line of code you want

q quit

Debugging in Perl

o Stepping & Tracing


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pp g g

s step -- execute 1 line of code. Steps oversubroutines.

n next -- execute 1 line of code.Steps into subroutines.

r return from function

Debugging in Perl

o Breakpoints


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b line set a breakpoint at line line b sub set a breakpoint at subroutine sub d line delete breakpoint D delete all breakpoints c [line] continue running until next breakpt[set a temporary breakpoint at line]

L List all breakpoints

Debugging in Perl

o Actions


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a linecmdexecutes perl code cmdeach time line is reached

A delete all line actions < cmdset action right before thedebugging prompt

> cmdset action right after the

debugging prompt

Debugging in Perl

How to Learn More


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o man perldebugo just try it!


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CGI Programming


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"CGI" stands for "Common Gateway Interface." CGI is a standard for interfacing external

applications with information servers, such as HTTPor Web servers .

CGI program is executable . A CGI program can be written in any programming

language, but Perl is one of the most popular,

CGI Programming


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CGI Programming

Steps To Create a CGI Program :


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File should be created in the cgi-bin/directory until unless we configure the webserver .

File should have execute permissions . First line should be perl interpreter

Next line should be print "Content-type:text/html\n\n";

CGI Programming

To avoid entering multiple print


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statements :print


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library . use CGI qw(:standard); header; start_html; end_html;


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CGI.pm Module

GET Method


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Param Post Sendmail


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Parsing XML documents

XML::Simple class exposes two methods,


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XMLin() and XMLout() . The XMLin() method reads an XML file orstring and converts it to a Perlrepresentation .

XMLout() method does the reverse, readinga Perl structure and returning it as anXML document instance .

Controlling parser behaviour

The ForceArray option is a Boolean flag

i


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that tells XML::Simple to turn XMLelements into regular indexed arraysinstead of hashes .

KeyAttr, which can be used to tell

XML::Simple to use a particular elementas a unique "key" when building the hashrepresentation of an XML document.

Database Connection

The DBI is a database access module for

h l i l


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the Perl programming language.

Notation and Conventions

$dbh Database handle object

$ th St t t h dl bj t


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$sth Statement handle object$drh Driver handle object$rows Number of rows processed (ifavailable, else -1)$fh A filehandle

undef NULL values are represented byundefined values in Perl\%attr Reference to a hash of attributevalues passed to methods

Database Connection

Connect :

$dbh DBI > t($d $


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$dbh = DBI->connect($dsn, $user,$password, { RaiseError => 1, AutoCommit=> 0 }); Prepare :

$sth = $dbh->prepare("SELECT * fromtable");

Available Drivers

DBD P PP P t SQL d i f th DBI


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Gofer

DBD::PgPP PostgreSQL driver for the DBIDBD::mysql MySQL driver for the DBIDBD::SQLite Self Contained RDBMS in a DBIDBD::ODBC ODBC Driver for perl DBI

Creating a Process

Eval : eval (string);


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Eval : eval (string);system : system(list);fork : procid = fork();pipe : pipe (infile, outfile);exec : exec(list);

Terminating a Process

Die : die (message);


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Die : die (message);warn : warn (message);exit : exit (retcode);kill : kill (signal, proclist);

Execution Control Functions


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sleep : sleep (time);wait : procid = wait();waitpid : waitpid (procid, waitflag);

Signals Signals are a kind of notification delivered bythe operating system .

To Print list of signals available :

perl -e 'print join(" " keys %SIG) "\n"'


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perl e print join( , keys %SIG), \n$SIG{QUIT} = \&got_sig_quit; # call &got_sig_quit for every SIGQUIT$SIG{PIPE} = 'got_sig_pipe'; # call main::got_sig_pipe for every SIGPIPE$SIG{INT} = sub { $ouch++ }; # increment $ouch for every SIGINT$SIG{INT} = 'IGNORE'; # ignore the signal INT$SIG{STOP} = 'DEFAULT'; # restore default STOP signal handling


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IO::Socket

It very hard to write each function

The module IO::Socket provides an easy


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The module IO::Socket provides an easyway to create sockets which can then beused like file handles

perldoc IO::Socket

Socket Programming

Net::Ping ModuleN t T l t M d l


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Net::Ping Module Net::Telnet Module Net::FTP Module Net::SSH::Perl Module


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Documents

Ashish Kumar Jha Brief Perl Tutorial