introduction to perl 2009

8/3/2019 Introduction to Perl 2009

1/109

2008 McAfee, Inc.

Introduction to Perl

Theres More Than One Way to Do It

MIC Automation Club


2/109

Confidential McAfee Internal Use Only

Agenda

Day-1Introduction to Perl

Variables

Operators

Array and Hash Functions

Conditions and Loop Operators

Day-2

Subroutines

File Operations and IO

Regular Expressions

Perl Built in functions

Day-3

Test

2/22/20122


3/109


Programming Methodologies

Structured or Method based C

Perl

Object Oriented

C++ Perl

Event Based

C#

VB

2/22/20123


4/109

What is Perl ?


5/109


What is Perl ?

Perl stands forPracticalExtraction andReportingLanguage.

Created in 1987 by Larry Wall.

Inspired from Unix like languages like Sed, Awk and Shell Script.

Most Perl Modules and scripts are platform independent.

C-Like syntax.

Perl is a freeware and open source.

2/22/20125


6/109


Slogan!!

The Perl slogan isThere's more than one way to do it

2/22/20126


7/109

How Do I Install and Run Perl?


8/109


How Do I Install and Run Perl?

Perl is available athttp://www.activestate.com/Products/ActivePerl/Download.html .

Command to execute a Perl program

For e.g. if Helloworld.pl is a Perl script

Perl Helloworld.pl

2/22/20128


9/109

Variables and Data types

$scalar

@array

%hash


10/109


Variables

Variables are storage containers for numbers, strings, and compoundstructures.

Perl supports three types of variables:

Scalars

Arrays

Hashes

A variable name can be up to 255 characters.

A variable name cannot start with a number

e.g. $64bitint (leading numbers not legal)

2/22/201210


11/109


Variables (contd..)

A minus sign is not legal in the variable namee.g. $file-handle (minus sign not legal)

Variable name cannot have special characters other thanunderscore(_)

e.g. $excangerateto (pound symbol not legal)

Here are some valid scalar variable names:

$A_Scalar_Variable

$scalarNo8

$_private_scalar

2/22/201211


12/109

Scalars ($)


13/109


Scalars

Scalar variables store a single value. They are prefixed with a $.

Consider this example:

$counter

$string=Hello world;

$string=HelloWorld;

$string=123;

$string=123.456;

2/22/201213


14/109

Arrays (@)


15/109


Arrays

An array is an indexed list of values with a consistent order.

Names of arrays are prefixed with @.

Examples of Arrays

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

@second_array = ('one', '2', 'three', '4', '5');

@a = qw(fred barney betty wilma);

2/22/201215


16/109

Hashes (%)


17/109


Hashes

Hashes are tables of key-value pairs.

They are also called associative arrays.

For example:

%hash = ('Mouse', 'Jerry', 'Cat', 'Tom', 'Dog', 'Spike');

2/22/201217


18/109

Arrays and Hash Functions


19/109



ValuesGrabs the values from the hash

@values = values(%hash);

Keys

Returns a list consisting of all the keys of the named hash.@keys = keys %hash;

The keys are returned in an apparently random order, but it is thesame order as either the values().

2/22/201219


20/109



shiftshift ARRAY

Shifts the first value of the array off and returns it, shortening the arrayby 1 and moving everything down. If there are no elements in thearray, returns the undefined value.

push

push ARRAY,LIST

Treats ARRAY as a stack, and pushes the values of LIST onto the endof ARRAY. The length of ARRAY increases by the length of LIST.Returns the number of elements in the array following the completedpush.

2/22/201220


21/109



popARRAYPops and returns the last value of the array, shortening the array byone element. If there are no elements in the array, returns theundefined value .

2/22/201221


22/109



deletedelete LIST

Deletes the specified keys and associated values from ahash, or the specified elements from an array. The operationworks on individual elements or slices.

For example:

delete $array[0];

Also note that when deleting an array item, only the itemsvalue is emptied; it doesnt remove the item from the list or

close the gap between the preceding and subsequent item(s).

2/22/201222


23/109



eacheach HASH

In a list context, returns a two-element list referring to thekey and value for the next element of a hash, allowing you

to iterate over it. In a scalar context, returns only the key forthe next element in the hash. Information is returned in arandom order.

2/22/201223


24/109



existsexists EXPR

Returns true if the specified hash key exists,regardless of the corresponding value, even if its

undef.

Returns in Scalar Context

0 if hash element or array index does not exist and1 if hash element or array index exists.

2/22/201224


25/109



joinjoin EXPR, LIST

Combines the elements ofLIST into a single string using thevalue ofEXPR to separate each element. It is effectively theopposite ofsplit. Note that EXPR is only interpolate between

pairs of elements in LIST; it will not be placed either beforethe first or after the last element in the string. To jointogether strings without a separator, supply an empty stringrather than undef.

2/22/201225


26/109



reversereverse LIST

In a list context, returns the elements ofLIST in reverseorder. In a scalar context, returns a concatenated string of thevalues ofLIST, with all bytes in opposite order.

Returns in Scalar Context Returns in List Context

String List

2/22/201226


27/109



scalarscalar EXPR

Forces the evaluation ofEXPR to be in scalar context, even ifit would normally work in list context

2/22/201227


28/109



splicesplice ARRAY, OFFSET, LENGTH, LIST

splice ARRAY, OFFSET, LENGTH

splice ARRAY, OFFSET

Removes the elements ofARRAY from the element

OFFSET forLENGTH elements, replacing the elementsremoved with LIST, if specified. IfLENGTH is omitted,removes everything from OFFSET onwards.

2/22/201228


29/109


List and Scalar Context

Every Perl expression is in one of two `contexts', either `list context' or`scalar context', depending on whether it is expected to produce a listor a scalar.

Example of list context:

($a,$b,$c)=(1,2,3);@arr=(4,5,6);

Example of scalar context:

$a=@arr;

$a=GetDate();


30/109

Operators


31/109


Operators

Basic arithmetic and logical operators

Assignment operator =

Arithmetic operators +-*/%**

Logical operators && || ! and or not Increment and decrement operators ++ --

Comparison operators == != < >= eq ne lt legt ge cmp

2/22/201231


32/109

Conditional Statements


33/109


Conditional Statements

Simple If

If else

Nested If else

else if ladder

unless

2/22/201233


34/109


Conditional Statements (contd..)

Simple if

if (EXPRESSION)

{

Statements;}

2/22/201234


35/109



The if-else condition

if (EXPRESSION)

{

Statements;

}

else

{

Statements;

}

2/22/201235


36/109



Nested if-else condition

if (EXPRESSION)

{if (EXPRESSION)

{

Statements;

}

else

{

Statements;

}

}

else

{Statements;

}

2/22/201236


37/109



else if ladder

if (EXPRESSION)

{Statements;

}

elsif (EXPRESSION)

{

Statements;

}

elsif (EXPRESSION)

{

Statements;

}

else{

Statements;

}

2/22/201237


38/109



Other forms of if statement

BLOCK if EXPRESSION;

STATEMENT if EXPRESSION;

STATEMENT, STATEMENT, STATEMENT if EXPRESSION;

2/22/201238


39/109



Unless statementunless(Expression)

{

Statements;

}

Unlike the if statement, the code block is executed only if theexpression is false rather than true.

2/22/201239


40/109

Loops


41/109


Loops

While Loop

while ()

{

Statements;

}

While loop executes as long as the expression is true and

once the expression is false, control exits the loop

2/22/201241


42/109


Loops (contd..)

Do While Loop

do{

Statements;

} while (expression);

do- while loop executes as long as the expression is true

and once the expression is false, control exits the loop.

Unlike while loop, do-while loop is executed at least once

irrespective of the truthness or falsity of the expression.

2/22/201242


43/109


Loops ( contd..)

Until Loop

until (EXPRESSION)

{

Statements;

}

until loop executes as long as the value of the expression is

false and exits the loop when the value becomes true.

2/22/201243


44/109


Loops (contd..)

For LoopPerl's for control structure is like the common for control

structure

you may have seen in other languages such as C. It looks

like this:

for (initialization; check; increment)

{

body;

}

2/22/201244


45/109


Loops (contd..)

foreach Loopforeach loop is same as for loop but does not require initialization andincrement as part of the declaration of the loop.

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

foreach(@array)

{print This is element $_\n;

}

2/22/201245


46/109

Loop controls


47/109


Loop controls

The last Operator

The last operator immediately ends the execution of theloop. (If you've used the "break" operator in C or a similarlanguage, it's like that.) It's the "emergency exit" for loop blocks.

Example:

for ($i=0;$i


48/109


Loop controls (contd..)

The next OperatorThe next control continues with the next iteration of the

loop (much like the "continue" operator in C or a similarlanguage):

Example:

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

if($i == 5)

{

next; #This will not print the value of $i and will goto the

#next value in the loop 6} print $i\n;

}

2/22/201248


49/109


Loop controls (contd..)

The redo Operator

The third member of the loop control triad is redo. Itsays to go back to the top of the current loop block, withouttesting any conditional expression or advancing to the nextiteration.

for($i=0;$i < 10;$i++)

####Redo comes here{

if($i == 5)

{

$i++;

redo; # This will execute the loop again if $i==5.

}print $i\n;

}

2/22/201249


50/109

Subroutines


51/109


Subroutines

Defining a subroutine

use the keyword sub, followed by the name of your subroutine,followed by a code block

sub Hello{

print Hello andWelcome to this world of Perl\n;

}

2/22/201251


52/109


Subroutines (contd..)

Passing arguments to subroutines

When arguments are passed to a subroutine they are stored inthe default variable @_.

Getting the arguments directly from the @_ array

sub Add

{

return $_[0] + $_[1];

}

Saving the arguments list into another set of variables or anotherarray

sub Add{

my ($num1,$num2)=@_;

return $num1+$num2;

}

2/22/201252


53/109



Using the Shift operator to get the arguments.

sub Add

{

my $num1=shift;

my $num2=shift;return $num1+$num2;

}

2/22/201253


54/109



Passing Lists to Subroutines. Because the @_ variable is an array, it can be used to supply lists

to a Subroutine.

All three of the following are valid:

@args = (2,3);

mysub(1,@args);@args = (1,2,3);

mysub(@args);

More than one list cannot be passed to a subroutine without using

References.

2/22/201254


55/109



The fundamental rule to remember is that when passing arrays orlists to subroutines you can pass only one array or list, and it mustbe the last argument supplied.

sub process {

my ($first, $second, @rest) = @_;

}

If you try to extract the array as the first element, then it willimmediately gobble up all of@_, even if there are arguments afterthe array leaving any scalar entries empty.

sub process {

my (@rest, $first, $second) = @_;

}

2/22/201255


56/109



Passing Hashes to Subroutines When you supply a hash to a subroutine, the hash is automatically

translated into a list of key/value pairs

For E.g.

sub display_hash

{my (%hash) = @_;

foreach (keys %hash)

{

print "$_ => $hash{$_}\n";

}

}

2/22/201256


57/109



The fundamental rule to remember is that when passing hashes tosubroutines you can pass only one, and it must be the last argumentsupplied.

This will not work.

sub display

{

my (%hash, $regex) = @_;

}

2/22/201257


58/109



Return Values

The return value of any block, including those used insubroutines, is taken as the value of the last evaluatedexpression. For example:

sub myfunc {

$_[0]+$_[1];

}The return value here is the result of the calculation.

You can also explicitly return a value using the return keyword:

sub myfunc {

my $c=$_[0]+$_[1];return $c;

}

2/22/201258


59/109


Subroutines (contd..) Return Context

In order to discover the context in which a function has beencalled, you use the wantarray function.

For E.g.

sub hw {

if (wantarray) {return('Hello','World',"\n");

}

else {

return "HelloWorld\n";

}

}

2/22/201259


60/109



Prototypes

A prototype definition is a parenthesized list of charactersmirroring the Perl variable type syntax (that is, $, @, %, and soon). It is placed after the sub keyword and subroutine name butbefore anything else, be it a subroutine definition, declaration, oranonymous subroutine:

sub mysub (PROTOTYPE); # subroutine declaratio

sub mysub (PROTOTYPE) {...} # subroutine definition

$subref = sub (PROTOTYPE) {...} # anonymous subroutine

For E.g.

sub volume ($$$) {

# ... as before ...

}

2/22/201260


61/109



Prototypes can decide the parameter sequence.

If the function has to receive a certain type of parameter as the firstone then in the prototype definition it must be prefixed with a \(backslash)

E.g.

sub Add(\@$$); indicates that the first argument must be an arrayor list followed by two scalars.

2/22/201261


62/109



Prototypes can decide the mandatory and optional parameters.

Mandatory and optional parameters are separated by a ;(semicolon)

E.g.sub CircleArea($;$)

This indicates that the function takes in two parameters, out ofwhich one is mandatory

2/22/201262


63/109

Perl Modules


64/109


What are Perl Modules

Perl modules are discrete components of any Perl program. A module is distinguished by a unique Namespace

Modules can be written in two formats.

Procedural Programming

Object Oriented Programming

2/22/201264


65/109


Perl Module Structure

package ;

#Add the required modules to be used

use strict;

use warnings;

#Define the subroutine required

sub Loop ()

{

my $loopvalue=shift;

return $loopvalue + 100;

}

#End the subroutine with this numerical

1;

2/22/201265


66/109


Calling a Perl Module

use Lib::MyMod;

use strict;

use warnings;

MyMod::Loop(100);

2/22/201266


67/109

Working with Files


68/109


Working with Files

Opening a File open FILEHANDLE, EXPR

A filehandle is a named internal Perl structure thatassociates a physical file with a name.

A filehandle can be reused.

It is not permanently attached to a single file, nor is itpermanently related to a particular file name.

The name of the filehandle and the name of the file are notrelated.

As far as Perl is concerned, all operating systems support

three basic filehandlesSTDIN, STDOUT, and STDERR

2/22/201268


69/109


Working with Files

Open a File in Read only Mode:

open (FH,< Data.txt);

open (FH,Data.txt );

Open a File inWrite Mode:

open (FH,> Data.txt);

This will Clear all the contents of a file before writing thenew contents.

2/22/201269


70/109


Working with Files

Open a File for appending:

open (FH,>> Data.txt );

Open a File in both Read andWrite Mode:

To open a file for both reading and writing prefix the > or < with a +sign.

open(FH,+< Data.txt );

2/22/201270


71/109


Working with Files

Reading Files

Reading in Scalar context

Open (FH,Data.txt);

My $Line=;

Print $Line;

open(FH,Data.txt)

While()

{

Print ;

}

2/22/201271


72/109


Working with Files

Reading Files in List Context.

When in a list context all the line from the filehandle and stored inthe list.

For e.g.Open(FH,Data.txt)

My @Lines=;

Print @Lines;

2/22/201272


73/109


Working with Files (contd..)

Writing to a File

Open(FH,> data.txt);

Print FH This is a test\n;

Closing a FileHandle

Close(FH);

2/22/201273


74/109


Working with Files

AutoFlush The amount of data that is read from a file or written to a file isdecided by the operating system. This is done for performancereasons and so that data is written in blocks. By default theautoflush is set to False.

Open(FH,> Data.txt);

Select(FH);

$|=1;

Print FH This is a test for autoflush enabled\n;

Alternaively the module IO::Handle can be used for this,

use IO::Handle;

open(DOOR,"


75/109



Handling Errors while opening files

Using the keyword die

Open(FH,Data.txt) or die $!;

This will exit the program if the file cannot be opened. The systemerror message is stored in $!.

The user can also defined his own custom message when theerror occurs.

Open(FH,Data.txt) or die File Failed to open. Error $!;

2/22/201275


76/109



Handling Errors while opening files

Using the Keyword warn

The warn keyword will also throw an error but will not quit the

program, the execution will continue from there on.

Eg:

Open(FH,Data.txt) or warn File open error $!\n;

2/22/201276


77/109



Reading the contents of a directory

opendir(DIR,C:\\Program files);

my @Contents=readdir(DIR);

closedir(DIR);

shift(@Contents); #Remove the . & .. symbols

shift(@Contents);

print @Contents;

2/22/201277


78/109


Working with Files (contd..) File Test Operators

Operator Description

-f Is it a File?

-T Is it a text file?

-X Is the file executable?

-d Is the file a directory?

-e Does the file exist?

-s Returns the size of the file, withzero referring to an empty file.

-z Is the file size zero?

2/22/201278


79/109

Regular Expressions


80/109


Regular Expressions

The regular expression, also called regex or regexp, is a syntaxfor expressing search patterns for finding and extractingmatches within text. Regexps have a long history, and Perl simplementation.

A key to writing good regular expressions is to understand the

guiding principles of how the engine seeks a match. Perl sregular expression engine works on three basic principles, inthis order:

Eagerness: It will try to match as soon as possible.

Greediness: It will try to match as much as possible.

Relentlessness: It will try every possible combination beforegiving up.

2/22/201280


81/109


Regular Expressions (contd..)

Uses of Regular Expressions

Pattern Matching (m//)

Pattern Substitution (s///)

Transliteration (tr///)

2/22/201281


82/109



Pattern Matching

The match operator, m//, is used to match a string or statement to aregular expression.

For example, to match the character sequence foo against the scalar$bar, you might

use a statement like this:

if ($bar =~ m/foo/)

2/22/201282


83/109


Regular Expressions (contd..)Modifier Description

I Makes the match case insensitive

m Specifies that if the string has newlineor carriage return characters, the ^

and $ operators will now matchagainst a newline boundary, instead of

a string boundary

o Evaluates the expression only once

s Allows use of . to match a newlinecharacter

x Allows you to use white space in the

expression for clarity

g Globally finds all matches

83 2/22/2012


84/109



Quantifiers

* Match 0 or more times + Match 1 or more time

? Match 0 or 1 time

{n} Match exactly n times

Character Class shortcuts \d [0-9] A digit

\D [^0-9] A non digit

\s [\s\t\r\f] A whitespace character

\S [ \s\r\t\f] A non whitespace character

\w [0-9a-zA-Z] A word character \W [^ 0-9a-zA-Z] A non word character

2/22/201284


85/109



Pattern Matching in Scalar Context

$true = ($foo =~ m/foo/);

Will set $true to 1 if$foo matches the regex, or 0 if the match fails.

Pattern Matching in list Context

my ($hours, $minutes, $seconds) = $time =~ m/(\d+):(\d+):(\d+)/;

2/22/201285


86/109



The $` $& and $ variables

The $` variable has the string to left of the pattern match.

The $& has the matched string.

The $ has the string to the right of the pattern match.

2/22/201286


87/109



The Substitution Operator

The substitution operator, s///, is really just an extension of the matchoperator that allows you to replace the text matched with some newtext. The basic form of the operator is

s/PATTERN/REPLACEMENT/;

For example, we can replace all occurrences of dog with cat using

$string =~ s/dog/cat/;

2/22/201287


88/109



Note that the return value from any substitution operation is thenumber of substitutions that took place. In a typical substitution,this will return 1 on success, and if no replacements are made,then it will return 0a false response.

The problem with modifying strings in this way is that weclobber the original value of the string in each casewhich is

often not the effect we want. The usual alternative is to copy theinformation into a variable first, and then perform thesubstitution on the new variable:

$newstring = $string;

$newstring =~ s/cat/dog/;

or on a single line

($newstring = $string) =~ s/cat/dog/;

2/22/201288


89/109



Transliteration or Translation (tr///)

Transliteration is the process of replacing one letter withanother.

Like the substitution operator they can be used with any suitabledelimiters, are bound to the input text with =~, have search and

replace criteria, and even accept modifiers. The left-hand side of a transliteration is not a pattern but a list of

characters to be transformed (that is, transliterated), and theright-hand side is the list of characters that they are transformedinto.

Each character on the left-hand side is converted into thecorresponding character on the right, determined by theirrespective positions in the left and right lists.

2/22/201289


90/109



Transliteration converts the letter a into the letter z, the letter b into theletter y, and the letter c into the letter x:

$text =~ tr/abc/zyx/;

If the replacement list is longer than the search list, then the trailingcharacters are ignored. If shorter, Perl repeats the final character untilthe replacement list is long enough:

$text =~ tr/abcd/zy/;

The return value from a transliteration is a count of the number ofsuccessful translations.

2/22/201290

P l I B ilt F ti


91/109

Perl In Built Functions


92/109



1. abs

abs EXPR

Returns the absolute value ofEXPR or$_.

2. binmode

binmode FILEHANDLE.

Sets the file read/write to binary mode.3. chdir

chdir EXPR

Changes the current working directory to EXPR. Returns 0 on failureand 1 on success.

2/22/201292


93/109


Perl In Built Functions4. chomp

chomp EXPR

chomp LIST

chomp

Removes the last character if it matches the value of$/ fromEXPR, each element ofLIST, or$_ if no value is specified.Returns Integer, number of bytes removed for all strings.

5. chopchop EXPR

chop LIST

chop

Removes the last character from EXPR, each element ofLIST,or$_ if no value is specified. Returns the the characterremoved from EXPR.

2/22/201293


94/109



6. crypt

crypt EXPR,SALT

Encrypts the string EXPR using the system crypt( ) function. The

value ofSALT is used to select an encrypted version from one of anumber of variations. Note that there is no equivalent decryptionfunction. You cannot (easily) decrypt a string that has beenencrypted in this way. Its normally used one way, first to encrypt astring, and then to encrypt a password to compare against theencrypted string. If youre using it in this

form, then consider supplying the encrypted password as theSALT.

2/22/201294


95/109



7. defined

defined EXPRdefined

Returns true if EXPR has a value other than the undef value, orchecks the value of $_ if EXPR is not specified. This can be

used with many functions to detect a failure in operation, sincethey return undef if there was a problem. A simple Boolean testdoes not differentiate between false, zero, an empty string, orthe string 0, which are all equally false. If EXPR is a function orfunction reference, then it returns true if the function has beendefined.When used with entire arrays and hashes, it will notalways produce intuitive results. If a hash element is specified, it

returns true if the corresponding value has been defined, butdoes not determine whether the specified key exists in the hash

2/22/201295


96/109



8. eof eof FILEHANDLEeof()

eof

Returns true if the next read on the specified FILEHANDLE will

return an end-of-file condition, or ifFILEHANDLE is not currently

associated with an open file. IfFILEHANDLE is not specified, it

returns the condition for the last accessed file. In Scalar Context:

undefifFILEHANDLE is not at end of file 1 ifFILEHANDLE will

report end of file on next read.

2/22/201296


97/109



9. eval

eval EXPR

Evaluates EXPR at execution time as ifEXPR were a separate Perlscript. This allows you to use a separate, perhaps user-supplied,piece of Perl script within your program. An eval EXPR statement isevaluated separately each time the function is called. . Anyexceptions raised by the interpreter, die, orwarn are contained in$@.

2/22/201297


98/109



10. exec

exec EXPR LISTExecutes a system command (directly, not within a shell) and neverreturns to the calling script.

11. exit

exit EXPREvaluates EXPR, exits the Perl interpreter, and returns the value asthe exit value.Always runs all END{} blocks defined in the script(and imported packages) before exiting. IfEXPR is omitted, thenthe interpreter exits with a value of 0. Should not be used to exitfrom a subroutine; use die or use return.

2/22/201298

P l I B ilt F ti


99/109



12. gmtimegmtime EXPRgmtimeReturns a list of values corresponding to the date and time asspecified by EXPR, or date and time returned by the time function ifEXPR is omitted, localized for the standard Greenwich mean time.The values returned are as follows:

($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =gmtime(time);

The array elements are numeric, taken from the system struct tm.The value of $mon has a range of 0..11, $wday has a range of 0..6(SundaySaturday), and $year is returned as the number of yearsfrom 1900.

2/22/201299

P l I B ilt F ti


100/109



13. hex

hex EXPR

hex

Interprets EXPR as a hexadecimal string and returns the value,or converts $_ ifEXPR is omitted.

14. intint EXPR

int

Returns the integer element ofEXPR, or$_ if omitted. The intfunction does not do rounding. If you need to round a value up toan integer, you should use sprintf

2/22/2012100

P l I B ilt F ti


101/109



15. index

index STR, SUBSTR, POSITION

index STR, SUBSTR

Returns the position of the first occurrence ofSUBSTR in STR,starting at the beginning (starting at zero), or from POSITION ifspecified.


-1 on failure

Position of matching string (starting at zero for the first character).

Also see rindex

2/22/2012101

P l I B ilt F ti


102/109



16. length

length EXPR

length

Returns the length, in characters, of the value ofEXPR, or$_ if not specified. Use scalar context on an array or hashif you want to determine the corresponding size.

2/22/2012102

P l I B ilt F ti


103/109



17. mkdir

mkdir EXPR,MODEMakes a directory with the name and path EXPR using themode specified by MODE,which should be supplied as an octalvalue for clarity.

Return in Scalar Context

0 on failure

1 on success18. ord

ord EXPR

ord

Returns the ASCII numeric value of the character specified by

EXPR, or$_ if omitted

2/22/2012103

P l I B ilt F ti


104/109



19. rand

rand EXPR

rand

Returns a random fractional number between 0 and the positivenumberEXPR, or 1 if not specified. Automatically calls srand toseed the random number generator unless it has already beencalled.


Floating point number.

2/22/2012104



105/109



20. rmdir

rmdir EXPR

rmdir

Deletes the directory specified by EXPR, or$_ if omitted. Onlydeletes the directory if the directory is empty.

2/22/2012105



106/109



21. split

split /PATTERN/, EXPR, LIMIT

split /PATTERN/, EXPR

split /PATTERN/

split

Splits a string into an array of strings, returning the resultant list. Bydefault, empty leading fields are preserved and empty trailing fieldsare deleted.

2/22/2012106



107/109



22. system

system PROGRAM, LIST

system PROGRAM

Executes the command specified by PROGRAM, passing LIST asarguments to the command. The script waits for execution of thechild command to complete before continuing. IfPROGRAM is theonly argument specified, then Perl checks for any shellmetacharacters and, if found, passes PROGRAM unchanged to theusers default command shell.

2/22/2012107



108/109



23. time

time

Returns the number of seconds since the epoch (00:00:00 UTC,January 1, 1970, for most systems; 00:00:00, January 1, 1904, forMac OS). Suitable for feeding to gmtime and localtime.

2/22/2012108

Thank You!!


109/109

Thank You!!

introduction to perl 2009

Documents