Learn Perl Language

7/29/2019 Learn Perl Language

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Perl

• Introduction

• Scalar Data

• Array

• Flow Control• File I/O

• Regular Expression• Subroutine



INTRODUCTION

• PERL : Practical Extraction andReport Language

• First developed by Larry Wall … subsequently by PERL Community

• Although continuously evolving, current version is 5.005_03 ( Perl 5 )

• Supported by Unix, Windows, Macintosh and LINUX

• Freely available on Internet (www.perl.com)

• Open Source language - Source Code available on the Net!!!!



• System Administration jobs

• Text/Document Processing

• Web programming

• Client-Server programming for Internet

• Database Interface(Oracle, Sybase, Informix, MySQL etc.)

• GUI programming on X Windows ( with Tk )

POPULAR PERL TASKS



POPULAR PERL TASKS

• Text/Document Processing• Examples:

• Assembler Development --> perl utility takes

input file(assembly language) and produce binarycode(machine language).

• To convert a code from VHDL to Verilog.



CHECKING PERL VERSION

perl -v



PERL OPTIONS

OPTION MEANING

-v Displaying Perl version

-e Execute perl code directly -c Check syntax but do not execute

-w Execute and show warning message



RUN INTERACTIVE PERL

$ perl -e ‘ print “hello world\n” ’

$ perl

print “hello world\n”

d



FIRST PERL SCRIPT

$ perl first.pl #!/usr/bin/perl

print “hello world\n” ;



EXECUTE PERL SCRIPT

$ perl -c first.pl Check first.pl syntax only

$ perl -w first.pl

Execute and show warning message



2 : SCALAR DATA• Scalar Data• Scalar Variable

• Scalar Operator• How to show output

• How to get input



NUMBER LITERAL

• Integer ; Floating Point• Integer : 1 , -9000 , 2343

• Floating Point : 1.99 , -3.25e10 ,900E200





PRINT COMMAND

$ perlprint “hello world” ;

print “Welcome to Perl\n” ;print ‘Enjoy yourself \n’

Result:hello world W elcom e to Perl

Enjoy yourself\nved4:/ohm /users/… .



ALTERNATIVE QUOTES

• Single quote can use q/……./• Double quote can use qq/……../

$ perl

print q/This is single quote/ ;

print qq/This is double quote\n/ ;D



PERL ESCAPE

SEQUENCES

ESCAPE SEQUENCE MEANING \n New line

\t Horizontal tab

\b Backspace \a Alert (Bell)

\cC Control C

\e Escape

\\ Backslash

\” Double Quote





PRINT EXAMPLE

$ perlprint “\lFIRST LINE\n”; fIRST LINE

print “\LCOMPUTER\E \n” ; computer

print “\uthailand\n”; Thailandprint “\Uindia is great\n”; INDIA IS GREAT

D



SCALAR VARIABLE

• Scalar variable : $• examples:

$x$AveryLongVariableName

$day_in_month$year2000



NUMERIC OPERATORS

PRECEDENCE

**

* / %

+ -





ASSIGNMENT OPERATORSSYNTAX : variable = value ;

$ perl

$a = 10 ; # This is comment$b = 20 ;

$c = $a + $b ;

print “$c\n”; # Same as print $a + $b , “\n” ;



BINARY ASSIGNMENT OPERATORS

SYNTAX : variable op= value

$ perl

$b = 100 ;

$a += 3 ;

$b *= $a ;print “$a\t$b\n”;

AUTOINCREMENT &



AUTOINCREMENT &

AUTODECREMENT

SYNTAX : ++variable , variable++ ,

--variable , variable--

$ perl$a = 10 ; $b = 20 ;

++$a ; #$a has value 11

$c = $b++ ; #$c is 20 , $b is 21

--$c ; #$c is 19



STRING OPERATOR• String Concatenation ( . )

“/etc” . “/” . “passwd” ==> “/etc/passwd”

$b = $c . “\n”

• String Repetition Operator ( x )

print “*” x 10 ;

print “<“ x 30 ;



COMPARISON

OPERATORSNumeric String Meaning

== eq Equal

!= ne Not equal

< lt Less than

<= le Less than or equal to

> gt Greater than>= ge Greater than or equal to



HOW TO GET INPUT name1.pl

print “Enter your name : ” ;

$name = <STDIN> ;

print “Enter your surname : ”;

$surname = <STDIN> ;

print “Your name is $name and surname is$surname” ;



CHOP() & CHOMP()• chop() remove the last character from the variable

$x = “espresso” ;

chop($x) ; # $x is now “espress”

• chomp() remove the end of record marker (“\n”) from thevariable

• chop($var = <STDIN>) ;chomp($var = <STDIN> ) ;

CHOP( ) & CHOMP( )



CHOP( ) & CHOMP( )

EXAMPLE

name2.pl

print “Enter your name : ” ;

$name = <STDIN> ; chop($name) ;

print “Enter your surname : ” ;

chomp($surname = <STDIN>);

print “Your name is $name and surname is$surname\n”;



3 : ARRAY• Array Literal• Array Variable

• Element access on Array• Operations on Array

• Command line argument



ARRAY LITERAL

array : ( value1, value 2, value 3 , … ,valuen )

or ( value 1 .. value n )

array :

( 1 , 2 , 3 , 4 , 5 ) or ( 1..5 )

(‘one’,’two’,’three’)

( $a , $b , $c )

( “Jan” , 1 , ”Feb” , 2 , “Mar” , 3)



ARRAY VARIABLEArray Variable : @name

$ perl

@day =(“mon”,”tue”,”wed”,”thu”,”fri”,”sat”,”sun”) ;

print “@day\n”;

@x = (1..100) ;

print @x ;



ARRAY ASSIGNMENT

@a = (’a’..’z’) ;

($a,$b,$c) = ( 10 , 20 , 30 ) ; # $a=10, $b = 20 , $c = 30

@b = @a ; # copy array

$a = @a ; # $a get length of @a($a) = @a ; # $a get first element of @a

($x,$y) = ($y,$x) ; # Swap $x and $y

@z = () ; # Null list



ARRAY ELEMENT ACCESS

$array[index] ; elementarray1.pl

@a = (‘red’ , ‘green’ , ‘blue’) ;

print “First element is $a[0] \n”;

print “Second element is $a[1] \n”;

print “third element is $a[2] \n”;print “Last index is $#a \n”; # Array

length = $#a + 1



ARRAY SLICE

@array[list]slice.pl@a = ( ‘a’..’z’) ;print “@a[0,1,2] \n”; # The same as @a[0..2]print “@a[0..$#a] \n”; # The same as @a

@b = @a[0..10] ;print “@b\n”;



OPERATIONS ON ARRAY

• push( ) and pop( )• shift( ) and unshift( )

• reverse( )

• sort( )



PUSH( ) & POP( )push():

• Takes a scalar and an array name as parameters• It pushes the value of the scalar at the end of the array

• Syntax: push(@array,variable or array) ;

pop():

• Takes an array name as a parameter

• It returns the top or the last element of the array• It removes element permanently from the array

• Syntax: $variable = pop ( @array ) ;



EXAMPLES$ perl

@a = (1..10) ;

push(@a,100) ;

print “@a\n”;

$ perl

@a = (1..10) ;

$y = pop ( @a ) ;

print “$y\n@a\n” ;



PUSH( ) AND POP ( ) EXAMPLEpushpop.pl

@a = (1..10) ;

print “Enter your data to push : ” ;

chop($a = <STDIN>) ;

push(@a,$a) ; print “ Now \@a has value @a \n”;

$y = pop (@a) ;print “ \$y has value $y and \@a has value @a \n”;



SHIFT( ) & UNSHIFT( )unshift():

• Takes a scalar and an array name as parameters

• It puts the value of the scalar at the beginning of the array

• Syntax: unshift(@array,variable or array) ;

shift():

• Takes an array name as a parameter• It returns the first element of the array

• It removes element permanently from the array

• Syntax: $variable = shift ( @array ) ;



EXAMPLES$ perl

@a = ( 1..10 ) ;

$x = shift ( @a ) ;

print “$x\n@a\n” ;

$ perl

@a = ( 10..20 ) ; @b = ( 100..105 ) ;

unshift( @a, @b ) ;

print “@a\n”;



SHIFT( ) & UNSHIFT( )

EXAMPLE

shift.pl

@a = (1..10) ; @b = (‘a’.. ‘z’) ;

unshift(@a,@b) ;print “Now \@a has value @a\n”;

$x = shift (@a) ;

print “\$x has value $x and \@a has value @a \n”;



REVERSE( )Syntax: reverse(@array)

$ perl

@a = (‘a’.. ‘z’) ;

@b = reverse (@a) ; print “@b\n”;

@a = reverse (@a) ; print “@a\n”;



SORT( )Syntax: sort(@array)

sort1.pl

@a = (‘batman’, ‘robin’, ‘batgirl’, ‘freeze’, ‘poison ivy’) ;

@b = sort (@a ) ; print “@b\n”;

@c = (1,2,3,10,15,25) ;

@d = sort (@c ) ; print “@c\n”;



COMMAND LINE ARGUMENTSpecial array variable : @ARGV

The script name : $0

arg.pl

print “The script name is $0 \n”;

print “All command line argument are @ARGV \n”;



SIMPLE ECHO PROGRAM$ echo A B C D E F

A B C D E F

$ perl -e ‘ print “@ARGV\n” ’ A B C D E FA B C D E F



READ INPUT AS ARRAY

$a = <STDIN> ; scalar context

@a = <STDIN> ; list context

DETERMINE ARRAY



DETERMINE ARRAY

LENGTH1. Use scalar( ) operator

Ex : @a = (‘one’,’two’,’three’) ;

print scalar( @a ) , “\n” ;

2. Use $#ArrayNamevariable ( last index )

Ex : @arr = (‘athena’ , ‘apollo’ , ‘hercules’ ) ;

print $#arr + 1 , “\n” ;



4 : FLOW CONTROL• if & unless structure

• while & until & for structure

• foreach structure

• last & redo & next structure• Logical Operators



TRUE AND FALSE IN PERL• Any string is true except for "" and "0"

• Any number is true except 0

• Any reference is true

• Any undefined value is false



TRUE AND FALSE EXAMPLE

• 0 False

• 0.00 False

• “0.00” True

• 10 True

• 23-23 False



IF STRUCTURE

if ( condition) { statement;

}else {

statement; }



CHECKING TRUE OR FALSE$ perl

print “Enter value : ” ;

chop($val = <STDIN> );

if ( $val ) {print “$val is true \n” ;

} else {

print “$val is false \n” ;

}

IF EXAMPLE



IF EXAMPLEif1.pl

print “Enter your status : ” ;chop($status = <STDIN>) ;if ( $status eq “single”) {

print “Welcome to Bachelor group \n”;

}

else {print “Congratulations !!! you are so lucky

\n”;



UNLESS STRUCTURE unless ( condition ) {

statement

} else { statement

}



IF -ELSIF STRUCTURE

if ( condition ) {

statement

}elsif ( condition ) { statement

}else{ statement

}



WHILE AND UNTIL while ( condition) {

….. repeat as long as true…………

}

until ( condition) {

….. repeat as long as false………..

}



WHILE EXAMPLEsum.pl

print “Enter number : ” ;

chop($n = <STDIN>) ;

$sum = 0 ;

while ($i <= $n) {

$sum += $i ; ++$i ;}

print “Sum from 1 to $n = $sum \n”;



ECHO MESSAGEquit.pl

print “Enter your message : ” ;

chop($mesg = <STDIN> ) ;

until ( $mesg eq “quit” ) {

print “You entered $mesg \n”;

print “Enter your message : ” ;chop ($mesg = <STDIN> ) ;

}

FOR STRUCTURE



for( initialization ; condition ; expression ) {……………………

}

Exam ple:$ perl

for ( $x = 0 ; $x <= 10 ; ++$x ) {

print “$x\n”;}

$ perl

for ( $y = 1 ; $y <= 100 ; $y += 1 ) {print “$y \n” ; print “********\n” ;

}





FOREACH STRUCTURE

foreach variable ( list ) { statement

………….}



FOREACH EXAMPLE1. foreach $x (1..10) { print “$x\n” ; }

2. foreach (1..10) { print “$_\n” ; }

3. for (1..10) { print ; print “\n” ; }

4. foreach ( reverse (1..10) ) { print ; }



LISTING EVEN NUMBER$ perl

foreach $x (1..100) {

if ( ( $x % 2 ) == 0 ) {

print “$x\n”;}

}



EXPRESSION MODIFIER• statement if condition ;

• statement unless condition ;

• statement while condition ;

• statement until condition ;



EXTRA FLOW CONTROLCOMMAND USAGE

goto label Jump to named labellast Break out of innermost loop ( break in C )

last label Break out of current loop at label

next Start next iteration of loop ( continue in C )next label Start next iteration of loop at label

redo Restart loop without re-evaluating condition

redo label Restart loop label without re-evaluatingcondition



ECHO MESSAGE AGAINquit2.pl

print “Enter your message : ” ;chop( $mesg = <STDIN> ) ;

for( ; ; ) {

last if ( $mesg eq “quit” ) ;

print “You enter $mesg \n”;

print “Enter your message : ” ;chop( $mesg = <STDIN> );

}



NEXT AND LAST EXAMPLE LINE : while ($line = <STDIN>) {

last LINE if ( $line eq “\n”) ;

next LINE if ( $line eq “#\n” );

}



LISTING EVEN NUMBER$ perl

foreach ( 1..100 ) {

next if ( $_ % 2 ) ;

print “$_ \n” ;}



LOGICAL OPERATORSEXAMPLE MEANING

$a && $b True if both $a and $b are true

$a || $b True if both or either one is true

!$a True if $a is false$a and $b The same as $a && $b

$a or $b The same as $a || $bnot $a The same as !$a



SHORT CIRCUIT OPERATOR1. if ( condition) {

statement ;

}

2. statement if condition ;

3. condition && statement ;

4. condition and statement ;



ARROW MESSAGEarrow.pl

$mesg = “TANSTAAFL” ;$num = 5 ;

for ( $k = 0 ; $k <= $num ; ++$k ) {

$blank = “ “ x $k ; print “\t$blank$mesg\n”;

}

for ( $k = $num - 1 ; $k >= 0 ; --$k ) {$blank = “ “ x $k ; print “\t$blank$mesg\n”;

}

5 : FILE INPUT/OUTPUT



/

• Angle <> Operator

• open( ) , close( ) and file handle

• File test operators

• File manipulation

• Directory manipulation

• Directory Handle



GETTING INPUT FROM STDIN

1. while ($_ = <STDIN>) {

print $_ ;

}2. while (<STDIN>) { print ; }

3. print while (<STDIN>) ;



ANGLE <> OPERATOR

<> get data from files in command line argument

or standard input (keyboard) .

“cat” in Perl

print while (<>) ;



CAT WITH FILENAME$ perl

print “$ARGV : $_” while ( <> ) ;



OPEN( ) AND FILE HANDLEopen(filehandle, filename) ;

COMMAND MEANING

open(FILE,”filename”) Open for readingopen(FILE,”<filename”) Open for reading

open(FILE,”>filename”) Create file andwrite to itopen(FILE,”>>filename”) Append to

existing file



DEFAULT FILE HANDLE

NAME MEANING

STDIN Standard Input (keyboard)STDOUT Standard Output (terminal)

STDERR Standard Error (same as STDOUT)



SIMPLE OPEN PROGRAM$ perl

open(PASSWD,“/etc/passwd”) ;print while ( <PASSWD> ) ;

$ perl

print “Enter filename :” ; chop($name = <STDIN>);

open(FILE,$name) ;

print while (<FILE> );



ERROR CHECKING WITH DIE1. unless(open(FILE,”filename”)) {

print “Can not open file \n” ;} else { ……….. }

2. unless (open(FILE,”filename”)) {

die “Can not open file” ;

}3. open(FILE, “filename”) || die “Can not open file” ;



CLOSE( )close(filehandle) ;

open(FILE,”filename”) or die “Can’t

read file “ ;while(<FILE>) {

……………….}

close(FILE) ;



WRITING TO FILEprint filehandle data

print “This is output \n” ;print STDOUT “This is output \n”;

print FILE “First line \n” ;



SIMPLE WRITE PROGRAM$ perl

open(LOG,”>log”) or die “Can not create log file ”;print LOG “This message go to log file \n”;

close(LOG) ;

$ cat log

This message go to log file



COPY FILE IN PERLcopy.pl

$source = $ARGV[0] ;$dest = “>“ . $ARGV[1] ;

open(INPUT,$source) or die “Can not read $source” ;

open(OUTPUT,$dest) or die “Can not create $dest” ;

while ( <INPUT> ) {

print OUTPUT $_ ;

}

close(INPUT) ; close(OUTPUT) ;



FILE TEST OPERATOROPTION MEANING

-r File or directory is readable-w File or directory is writable

-x File or directory is executable

-e File or directory exists

-z File exists and has zero size

-s File exists and return size in byte

-f File is a plain file

-d File is a directory



FILE TEST OPERATOR ( 2 )OPTION MEANING

-l File is a symbolic link-b File is a block special file

-c File is a character special file

-u File or directory is setuid

-g File or directory is setgid

-T File is text file

-B File is binary file

-M Modification age in days



GETTING FILE SIZE$ perl

print “Enter file name : ” ;chop($name = <STDIN> );

if ( -f $name ) {

$size = -s $name ;

print “$name has size = $size \n”;

}



FILE CHECKING EXAMPLEprint “Enter file name :” ; chop($name = <STDIN>) ;

print “$name is readable \n” if ( -r $name ) ;

print “$name is writable \n” if ( -w $name ) ;

print “$name is executable \n” if ( -x $name ) ;

if ( -f $name ) {

$size = -s $name ;

print “$name is file and has size = $size \n” ;

} elsif ( -d $name ) {

print “$name is directory \n”;

}



6 : SUBROUTINE• Defining subroutine

• Global and local variable

• Passing and accessing parameter

• Recursive function• Sorting in Perl

DEFINING SUBROUTINE



DEFINING SUBROUTINE

sub subname {

statement 1;statement 2 ;

} &subname;

SIMPLE EXAMPLE



SIMPLE EXAMPLE$ perl

sub X {print “Subroutine example\n”;

}&X ;

SUBROUTINE EXAMPLE



SUBROUTINE EXAMPLE

sub myfunc {print “Message in subroutine \n”;

}print “Before invoking subroutine \n” ;

&myfunc ;

print “After invoking subroutine \n”;



FINDING SUM



FINDING SUMsub mysum {

@number = (1..100) ;foreach (@data) {

$sum += $_ ;

}

$sum ;

}$total = &mysum ;

print “Total = $total \n” ;

GLOBAL VARIABLE



GLOBAL VARIABLE$a = 100 ;

$b = 200 ;$sum = &add ;

print “$a plus $b = $sum \n”;

sub add {

$total = $a + $b ;

$total ;}

GLOBAL VARIABLE ( CONT )



GLOBAL VARIABLE ( CONT. )$x = 100 ;

print “Before invoking : \$x = $x \n” ;&showvalue ;

print “After invoking : \$x = $x \n” ;

##################

sub showvalue {

$x = 999 ;print “In function : \$x = $x \n”;

}

LOCAL VARIABLE



LOCAL VARIABLE$x = 100 ;

print “Before invoking : \$x = $x \n”;&showvalue ;

print “After invoking : \$x = $x \n”;

##########################sub showvalue {

my ($x) = 999 ;

print “In function : \$x = $x \n” ;

}

SPECIAL ARRAY @



SPECIAL ARRAY : @_

• All parameter passing to subroutine are in @_ array

• First parameter = $_[0] ,Second parameter = $_[1] , and so on

PASSING PARAMETER



PASSING PARAMETER$value = &multiply(10,20) ;

print “ 10 multiply 20 = $value \n”;sub multiply {

my ($first) = $_[0] ;

my ($second) = $_[1] ;

#### or my($first,$second) = @_ ;

my ($product) = $first * $second ;$product ;

}

PASSING ARRAY PARAMETER



PASSING ARRAY PARAMETER$sum = &add(1..100) ;

print “ Sum is $sum \n”;sub add {

local($sum) = 0;

foreach (@_) {

$sum += $_ ;

}$sum ;

}

FACTORIAL EXAMPLE



FACTORIAL EXAMPLEfact.pl

if ( $ARGV[0] eq “ “) { die “Usage: $0 number \n”; }$sum = &fact($ARGV[0]) ;

print “ Factorial of $ARGV[0] = $sum \n”;

sub fact {my ( $sum ) = 1 ;

for ( $I = 1 ; $I <= $_[0] ; ++$I ) {

$sum *= $I ;}

}

RECURSIVE FACTORIAL



RECURSIVE FACTORIALrefact.pl

die “Usage : $0 number \n” unless (@ARGV) ;$result = &fact($ARGV[0]) ;

print “Factorial of $ARGV[0] = $result \n”;

sub fact {my ($num) = @_ ;

if ( $num == 0 or $num == 1 ) { 1 ; }

else { $num * &fact( $num - 1) ; }

}

FIBONACCI NUMBER



FIBONACCI NUMBERDefinition : F(0) = 0 ; F(1) = 1 ;

F(n) = F(n-1) + F(n-2) for n > 1sub Fib {

my ($num) = @_ ;

if ( $num == 0 ) { 0 ; }elsif ( $num == 1 ) { 1 ; }

else {

&Fib($num - 1) + &Fib($num - 2) ;

}

}

SORTING



SORTING

• Ascending : ‘a’ , ‘b’ , ‘c’ , …. , 1 , 2 , 3 , …• Descending : ‘Z’ , ‘Y’ , ‘X’ , … , 10 , 9 , 8 , ...

SORTING IN PERL



SORTING IN PERL1. @list = <> ;

@sortlist = sort @list ;print “@sortlist \n”;

2. @list = <> ;

print sort @list ;

3. perl -e ‘ print sort <> ; ’

ASCII SORT



ASCII SORT

@data = (1,13,2,15,10,30) ;

@newlist = sort @data ;

print “After sorting : @newlist \n”;

SORTING NUMERICALLY



SORTING NUMERICALLY1. Define a sort subroutine

2. 2 elements from list will be assigned to $a and $b3. Compare $a and $b

4. If $a is less than $b return -1If $a is equal $b return 0

If $a is larger than $b return 1

5. Use “sort routinename list” in main program

NUMERICAL SORT



NUMERICAL SORT@data = (1,13,2,15,10,30) ;

@newdata = sort number @data ;print “ After sorting : @newdata \n” ;

sub number {

if ( $a < $b ) { -1 ; }

elsif ( $a == $b ) { 0 ; }

else { 1 ; }}

SPACESHIP <=> OPERATOR



SPACESHIP <=> OPERATOR sub number {

$a <=> $b ;}

Sorting list of number from input

1. print sort number <> ;

sub number { $a <=> $b ; } ;

2. perl -e ‘ print sort { $a <=> $b ; } ; ’

7 : REGULAR EXPRESSION



7 : REGULAR EXPRESSION• Common regexp. meatacharacters

• Perl pattern matching

• Modifier and Backreference

• split( ) and join( )

REGEXP. CONCEPT



• A pattern or template to be matched against a

string• Regular Expression composed of 2 types of

characters• Normal text character ( Literal )

• Special characters or Metacharacter (

Grammar or Rule )

REGEXP COMMANDS



REGEXP. COMMANDS• Unix utilities : ed , grep , awk , sed , lex ,etc.

• Editors : vi , emacs ,etc.• Programming Languages : Perl , Tcl , Python

• Programming Environment : Delphi , VisualC++

GREP & FGREP & EGREP



GREP & FGREP & EGREP grep

global/regular expression/print : grep [ option ]

OPTION MEANING

-n Show linenumber

-i I nore case

GREP EXAMPLE



GREP EXAMPLE$ grep root /etc/passwd

$ grep -n “sub” *.pl

$ grep -I “from:” mbox

$ grep -v ksh /etc/passwd

METACHARACTERS



• Start and end of line

• Character Class• Matching any character

• Alternation• Quantifiers

^ (START) AND $ (END)



SYNTAX : pattern match pattern at start of line

pattern$ match pattern at end of line

EXAMPLE MEANING

line Match “line” at beginning of line

ksh$ Match “ksh” at end of line

test$ Match line that have only “test”$ Match empty line

EXAMPLE



$ egrep “ chop” *.pl

$ egrep “ksh$” /etc/passwd

$ egrep -n “ root” /etc/passwd

$ egrep “ $” *

CHARACTER CLASS : [ ]



SYNTAX : [ … ] or [ char1 - charN]

EXAMPLE MEANING

gr[ea]y Match gray or grey

<H[123456]> Match <H1> <H2>,<H3>,...,<H6><H[1-6]> The same as above

[a-z][0-9] Match any lowercase followed with a digit

[Tt]he Match the or The at beginning of line

NEGATED CHARACTER CLASS



SYNTAX : [ …..]

EXAMPLE MEANING

q[ u] Match q followed with any character except u

[ 0-9] Match any line that do not begin with number

DOT : MATCH A CHARACTER



EXAMPLE MEANING

file. Match “file” with a character

[0-9]. Match a digit with any character

aa.zz Match aa followed with any character and zzdd.mm.yy Match dd/mm/yy, dd-mm-yy ,dd:mm:yy , etc.

…$ Match any line that has 3 characters

| : ALTERNATIONS



SYNTAX : pattern |pattern | …..

EXAMPLE MEANING

grey|gray Match grey or gray

gr(e|a)y Match grey or gray (same as above)(First|1st) [Ss]treet Match “First Street” , “First street”,

“1st Street” , “1st street”

(From|To) : Match “ From :” or “ To :”

<(H|h)[1-6]> Match <H[1-6]> or <h[1-6]>

QUANTIFIERS



CHARACTER MEANING

* Zero or more of previous haracters

+ One of more of previous character

? Zero or one of previous character

( Optional )

STAR * : ZERO OR MORE



EXAMPLE MEANING

a* Matchnothing , a , aa , aaa, aaaa , etc.

abc* Matchab , abc , abcc , abccc , etc.

(abc)* Matchnothing , abc , abcabc , abcabcabc , etc. .* Match any character any number of times

x.*x Match any character that start and end with x

[ab]* Matchnothing,a,b, ab , ba , aba , aab ,bba ,etc. (a*|b*) Matchnothing ,a , b , aa , bb ,aaa, bbb , aaaa , etc.



? : OPTIONAL ITEM

EXAMPLE MEANING



EXAMPLE MEANING

ab? Matchaandab colou?r Matchcolor andcolour

J uly? Match J ul and J uly 30(th)? Match30and30th

fo+ba?r Match fobr, fobar, foobr , foobar ,etc

[-+]?[0-9]+ Match any integer with optional sign

PERL CHARACTER CLASSES

N E i l t Cl C d



Name Equivalent Class Code

Digit [0-9] \d

Word character [a-zA-Z0-9_] \w

Space character [ \t\n\r\f] \s

Not Digit [ 0-9] \D

Not word [ a-zA-Z0-9_] \W

Not space [ \t\n\r\f] \SWord boundary \b

Non word boundary \B

EXAMPLEEXAMPLE MEANING



EXAMPLEEXAMPLE MEANING

[-+]?\d+ Match an nteger with optional sign

the\s+the Matchdouble thewith at least one space

\d\d:\d\d\s(am|pm) Match time<\w+> Match any word within < and >

Q : Define IP Address pattern match

Q : What does <HR\s+SIZE\s*=\s*[0-9]+\s*> match ???

PATTERN RANGE { }

SYNTAX : pattern{min max}or pattern{min }or



SYNTAX : pattern{min , max} or pattern{min , } or

pattern{num}

EXAMPLE MEANING

X{1,5} Match X, XX, XXX, XXXX, XXXXX A{0,1} The same as A?

\d{0,} The same as \d*

\w{1,} The same as \w+

$\d{3}$\s+\d{7} Match telephone number with (code area)

PERL PATTERN MATCHING

SYNTAX :



SYNTAX :

1. if ( $var =~ m/pattern/ ) { …………….. }

2. if ( $var =~ m#pattern#) { …………….. }

2. if ( $_ =~ m/pattern/ ) { …………….. }3. if ( m/pattern/ ) { …...………. }

4. if ( /pattern/ ) { ……..…….. }

TINY GREP PRGORAM

grep1pl



grep1.pl

#This program check for pattern “http”

while ( <> ) {if ( m/http/ ) {

print ;

}

}

ANOTHER GREP PROGRAM

grep2pl



grep2.pl

die “Usage: $0 pattern file\n” if ( scalar(@ARGV) != 2 ) ;$pat = $ARGV[0] ;

$file = $ARGV[1] ;

open(FILE,$file) or die “Can not open file $file !!!” ;while ( $line = <FILE> ) {

if ( $line =~ m/$pat/ ) {

print “$line”

}

}

MATCHING URL

url1 pl



url1.pl

while (<>) {print if (/http:/) ;

print if (/ftp:/) ;print if (/mailto:/) ;

print if (telnet:/) ;

}

IGNORE COMMENT LINE

commentpl



comment.pl

open(FILE,”comment”) or die “Can not open file !!!\n”;

while ( <FILE> ) {

next if ( / #/ ) ;print ;

}

CHECKING INPUT

input pl



input.pl

for(;;) {

print “Enter your command : ” ;

chop($ans = <STDIN>) ;

last if ( $ans =~/ [qQ] / ) ;

#Same as ( <STDIN> =~ / [qQ]/ )}

CHECKING DIGIT

digit pl



digit.pl

print “Enter any digit : ”;

chop($reply = <STDIN> ) ;

if ( $reply =~ m#[0-9]+$#) {

print “$reply is digit \n”;

} else {print “$reply is not digit \n”;

}

MATCHING PHONE NUMBER

phone.pl



phone.pl

print “Enter telephone number : ” ;

chop($phone = <STDIN> );

unless ( $phone =~ m/ \d{7}$/ ) {print “$phone is not valid telephone number \n”;

}



HOW TO IGNORE CASE

Assume that we want to match either “y” or “Y” at beginning



y g g

of line.

1. Use /I syntax

if ($input =~ / y/I )2. Use alternation syntax […]

if ($input =~ / [yY]/ )

3. Use logical or operatorif ( $input eq “y” or $input eq “Y” )

REGEXP. REPLACEMENT

SYNTAX : s/regexp/replacement/



g p p

sub1.pl

$_ = “this is simple string” ;

s/string/sentence/ ; #Default with $_ print “$_ \n”;

$x = “From here to eternity” ;

$x =~ s/here/there/ ;print “$x\n”;

MATCH GLOBALLY WITH /g

SYNTAX : /pattern/g



p g

sub2.pl

$x = “Oh! captain my captain “ ;

$x =~ s/captain/CAPTAIN/g ;print “$x\n”;

$_ = “To be or not to be” ;

s/be/**BE***/gi ;print “$_\n”;

STRIP LEADING SPACE

strip.pl



open(FILE,”white.txt”) or die “Can not open file !!!\n”;

while (<FILE>) {

s/ \s*// ;print ;

}

close(FILE) ;

BACKREFERENCE

SYNTAX



/ (pattern) (pattern) …….. \1 \2 …../

/ (pattern) (pattern) …… /

{ $1 $2 ….. }

EXAMPLE

1. /red.blue./



Match “red” followed with any char. and “blue” and any char.

2. /red(.)blue\1/

Match “red” followed with a char. and “blue” and with same char.

3. /test(.*)prog\1/

Match “test” followed with any char. and “prog” and followed with

same sequence

4. /(\w+)\s*=\s*\1/

Match “foo=foo” , “hello = hello” , etc..

SWAP WORD

$ perl



$ p

$_ = “hello world”;s/(\w+)\W+(\w+)/\2 \1/ ;

print “$_\n”;

EXTRACT INFORMATION

$ perl



$_ = “This is a test” ;

/(\w+)\W+(\w+)/ ;

print “$1\n$2\n”;

$ perl

$_ = “Another example program” ;

($first , $second) = /(\w+)\W+(\w+)/ ;print “$first\n$second\n”;

SPECIAL VARIABLE

VARIABLE MEANING



$& Match part of string that match regexp.

$ Match part of string before $&

$’ Match part of string after $&

EXAMPLE

$ perl



$_ = “This is test on perl pattern matching” ;/p.*l/ ;

print “$&\n”;

print “$ \n”;

print “$’\n”;

SPLIT( )

SYNTAX : split ( /pattern/ , variable)



split /pattern/

split

$ perl$_ = “this is a test on split” ;

@char = split ; # The same as split ( /\s+/,$_ )

print “@char\n”;

EXTRACTING CHARACTER

SYNTAX : split(//,variable)



extract.pl

print “Enter your word : “;

chop($input = <STDIN>);

@word = split(//,$input) ;

foreach (@word) { print “$_\n”; }

PALINDROME EXAMPLE

palin1.pl

i t “E t d ” h ($ d STDIN )



print “Enter your word :” ; chop($word = <STDIN>) ;

@forw = split(//,$word) ;

@back = reverse @forw ;

for($I = 0 ; $I < scalar(@forw) ; ++$I ) {if ( $forw[$I] ne $back[$I] ) {

die “$word is not palindrome\n”

}}

print “$word is palindrome\n”;

HISTOGRAM EXAMPLE

hist.pl



open(DATA, “hist.dat”) or die “Can not open file !!!\n”;

while(<DATA>) {

@input = split ;print “$input[0]\t” ;

print “*” x $input[1] . “\n” ;

close(DATA) ;

FILE /etc/passwd

FORMAT

l i t d d id id t h di h ll



login:encrypted password:uid:gid:comment:home dir.:shell

EXAMPLE

root:x:0:0:ROOT:/:www:x:999:1:Web server account :/usr/users/www:/bin/ksh

lotus:x:1000:5:Kornkwan :/usr/users/lotus:/bin/csh

jaew:x:1001:1:Thanita:/usr2/users/jaew:/bin/bash



DIRECTORY SEARCH PATH

path.pl



$dirpath = $ENV{“PATH”} ;

@dirname = split (/:/ , $dirpath ) ;

foreach ( @dirname ) {

print “$_\n”;

}

J OIN( )

SYNTAX : join expr , list



$ perl

@list = (“bat” , “cat” , “penguin” ) ;

$animal = join(“:”,@list) ;

print “$animal\n”;

PALINDROME WITH J OIN()

palin2.pl

print “Enter yourword :” ; chop($word = <STDIN>) ;



print Enter your word : ; chop($word = <STDIN>) ;

@forw = split(//,$word );

$back = join(‘‘,reverse @forw) ;

if ( $word eq $back ) {print “$word is palindrome\n” ;

} else {

print “$word is not palindrome \n”;}

1.



/etc/passwd

1. account UID 0

2. UID

3. account

password

8 : HASH• Hash Literal and variable



• keys( ) operator• values( ) operator

• each( ) operator• exists( ) operator

• delete( ) operator

• Special Hash : %ENV

DEFINITION

• Hash ( Associative Array ) is an array that can be



accessed by key name• Each pair in hash is interpreted as key/value pair

HASH LITERLAL & VARIABLE

• Hash variable %



%ENV , %array• %day = (

“Mon”,”Monday”,”Tue”,”Tuesday”) ;

• access element hash $hash{$key}

•

$day{“Mon”}

“Monday”

ACCESS COLOR CODE

color.pl

%color =( “red” =>0X00F ,



%color ( red > 0X00F ,

“green” => 0X0F0 ,

“blue” => 0XF00 ) ;

#Same as ( “red”,0x00f,”green”,0x0f0,”blue”,0xf00 )print “Enter color name :” ;

chop($name = <STDIN>) ;

print “Code for $name is $color{$name} \n ”;

KEYS( ) OPERATOR

keys.pl



$assoc{“name”} = “Hari Seldon” ;$assoc{“addres”} = “Sterling University” ;

$assoc{“city”} = “Trantor” ;

@keyname = keys %assoc ;

print “@keyname \n”;

RETRIEVING KEYS

key2.pl

%comm = ( “ls”, ”dir”,”mv”, ”rename”,”rm,”del” ) ;



( , , , , , ) ;

foreach $key (keys %comm) {

print “Unix command $key has DOS command as$comm{$key} \n”;

}

VALUES( ) OPERATOR

value.pl



$capital{“Thailand”} = “Bangkok” ;

$capital{“Japan”} = “Tokyo” ;

$capital{“England”} = “London” ;@capital = values %capital ;

print “@capital \n”;

EACH( ) OPERATOR

each.pl



%money = ( “Thai” => “Baht” ,“America” => “Dollar ,

“Japan” => “Yen” ,

) ;while ( ($country,$name) = each %money) {

print “$country has money name as $name \n”;

}

EXISTS( ) OPERATOR

• Return true if the specified hash key exists in itshash



• Example :

print “Exists \n” if ( exists $hash{$key} ) ;

DELETE( ) OPERATOR

delete.pl



%bookcover = ( “Perl” => “Camel” ,

“Compiler” => “Dragon” ,

“Postscript” => “Red”) ;

delete $bookcover{“Postscript”} ;

print keys %bookcover ;

ENVIRONMENT VARIABLES

SPECIAL HASH : %ENV



env.pl

while ( ($key,$value) = each %ENV ) {

print “$key has value as $value \n”;

}

USEFUL ENVIRONMENT

VARIABLES

USEFUL ENVIRONMENT

VARIABLESNAME MEANING



LOGNAME Current login name

HOME Home directory

PATH Directory search path

SHELL Login shell

KNOWING OS NAME

osname.pl



use Config ;

$osname = $Config{‘osname’} ;

print “This machine run $osname as O.S. \n” ;

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