learn_perl_by_example(1).pdf

LearnPerlbyExample-PerlHandbook

forBeginners-BasicsofPerlScripting

Language

www.freebsdonline.com

2008/01/29

ThiscourseisaboutPerlProgrammingLanguage.ItisforbeginnersanditexplainPerl

basicsinaeasytolearnway.IfyouareasysadminandyoulearnLinuxorUNIXthisis

whatyouneedtobeabletowritePerlscripts,toknowalanguageeverysysadminmust

know.

PERLisapowerfulscriptinglanguage,verypopularamongUNIX/Linuxadmins.This

tutorialswilltrytocovereverythingyouneedtoknowinordertoprograminPerl.Perl

standsforPracticalExtractionanReportLanguage,itwasﬁrstusedastextprocessor,it

borrowsfeaturesfromC,shellscripting(UNIXsh),sed,awk,Lisp,Pascal.Itcanbeused

alsofordevelopingdyamicwebapplicationsasCGIs.

Thistutorialwasprovidedbyhttp://www.freebsdonline.com

Youmayfreelydistributethisdocumentinanyformwithoutchangingthetextor

removingcopyrightnotice.

LearnPerlbyExample-PerlHandbookforBeginners-BasicsofPerlScriptingLanguage

TableofContents

1Introduction.................................................................................................................................2

2PerlVariables..............................................................................................................................3

3Perlcontrolstructures................................................................................................................7

4Deﬁningandusingsubroutines................................................................................................10

5Usingﬁleparameters(positionalparameters).......................................................................11

6PerlRegularExpressions.........................................................................................................11

7AboutTutorial...........................................................................................................................15

1Introduction

PERLisapowerfulscriptinglanguage,verypopularamongUNIX/Linuxadmins.Thistutorials

willtrytocovereverythingyouneedtoknowinordertoprograminPerl.Perlstandsfor

PracticalExtractionanReportLanguage,itwasﬁrstusedastextprocessor,itborrowsfeatures

fromC,shellscripting(UNIXsh),sed,awk,Lisp,Pascal.Itcanbeusedalsofordeveloping

dyamicwebapplicationsasCGIs.

1.1FewthingstoknowbeforestartprogramminginPerl

Perlcodeisportable.Mostscriptsarewrittenforversion5.8orhigher.Whenstartprogramming

inPerlﬁrstyoumightwanttoﬁndthepathofPerlbinary.OnmostUNIX/Linuxsystemsyoucan

dothatwithwhereiscommand:

whereisperl

Asaresultofthiscommandyoumighthave:/usr/bin/perl.Soyourscriptsmusthaveﬁrstlineof

codewiththisvalue:

#!/usr/bin/perl

#restofcode#willbeusedforcomments.

Onﬁrstlineofsourcecodethislinewillhelpshellinﬁndingwhatbinarytousewhenrunningthe

script.

LearnPerlbyExample-PerlHandbookforBeginners-BasicsofPerlScriptingLanguage

Inordertoproperlyrunthescriptyoursourcecodemustalsohaveexecutableﬂagfortheuser

youusetorunthescript.Thiscanbeachievedforexampleforﬁleprog1.pladdingexecutable

ﬂagfromcommandline:

chownu+xprogr1.pl

So,tostartyourPerlscriptyouwillfollow:

a)Createanemptyﬁle:

touchprogram.pl

b)Addexecutableﬂagtothatﬁle:

chownu+xprogram.pl

c)FindwhereyourPerlbinaryis:

whereisperl

(youwillgetsomethinglike/usr/bin/perl).

c)Editthatﬁlewithyourtexteditor,andaddperlpathwiththissyntax:#!/usr/bin/perl(notthat#

onﬁrstlineofyourcodewillnotbeseenascomment)

editprogram.pl

andputthere:#!/usr/bin/perl.

Note: ForLinuxyoucanusenano,picoormcedit.EditisyourdefaulttexteditorinFreeBSD.Ifyouhaveinstalled

MidnightCommanderpackage,youcanusemcedit,whichisnice.

Note:usestrict; putinperlsourcecodewillforceustodeclarevariablesinamoresafe(proper)way.All

variablesmustbedeclaredwithmypreﬁx.

Note: Byadding-wto#!/usr/bin/perlitwillactivateperlwarnings,veryusefullfordebugging.

#!/usr/bin/perl-w

LearnPerlbyExample-PerlHandbookforBeginners-BasicsofPerlScriptingLanguage

2PerlVariables

Perlhas3typesofvariables:

• scalars;

• arrays;

• hashes;

2.1Scalars

ExampleonhowtodeﬁneascalarvariableinPerl:

$var1="value" #ascalarvariablevar1isdefinedandastring

#"value"isassignedtothatvariable;

$var2=100 #ascalarvariablevar2isdefined,andan

#integervalueisassigned.

Example:Toprintascalarvaluewewilluse:

print"$var1";

2.2Arrays

ExampleonhowtodeﬁneanarrayinPerl:

@array1=("Value1","Value2",Value3");

Exampleonhowtoprintanarray:

print"Ourarrayvariablecontains:@array1\n";

Inourexamplewe’veused\nescapechartoinsertanewline(escapecharscanbeusedthesame

wayareusedinClanguage).

Thepreviousexamplewilldisplayallvaluesfromarray1array.

Todisplayoneelementofthearray:

LearnPerlbyExample-PerlHandbookforBeginners-BasicsofPerlScriptingLanguage

print"Firstelementofthearrayis:$array1[0]";

Asyoumightnoticewe’vedeﬁnedarraywith@butprintedasinglevalueofthatarrayusing$.

Thisiscorrectbecausewewanttoprintasinglevalue.

Itisalsopossibletoprintmultiplevaluesfromanarray:

print"Ourarraycontains:@array1[0..2]";

Previousexamplewillprintelementsfrom0toelementnr.2fromarray1.

Youcanalsoprintmultipledistinctelementsfromarray:

print"Ourarraycontains:@array1[0,4,7]";

Thepreviousexamplewillprintonlyvaluesforelement0,4and7.Notethatinperlﬁrstvalueof

anarrayisnumber0.

Thatisﬁnebuthowdoweﬁndthenumberofelementsofanarray?

print"Numberofelementsofanarray:$#array1";

Notethat$#array1inourexampleisnumberofelements,butbecauseelementsfromanarrayin

Perlstartswithvalue0,therealnumberofelementsofanarrayis$#array+1.

Thereisanothermethodtodeﬁneanarray:

@array2=qw(Value1Value2Value3Value4);

Perlfunctionsforworkingwitharrays:

• pop-removelastelementofanarray:

• push-addanelementtotheendofarray;

• shift-removesﬁrstelementofanarray;

• unshift-addanelementtothebeginningofarray;

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