Perl Training References File Handling

8/13/2019 Perl Training References File Handling

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PERL(References and File Handling)


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Page 1

AGENDA

References File Operators

Reading From a File

Writing into FileAppending the File


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References - Preface

Need for more complex data structures, than simple variablesand lists

Perls 3 built-in types combine with references, gives

arbitrarily complex and powerful data structures

A selection between an elegant program doing its job quicklyand a program that consumes system resources voraciously


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What is a Reference?

A reference is a scalar value that points to a memory location ofanother variable in memory.

$b$a 5

0x305108 0x351f00

Reference Referent


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Creating a Reference

$b$a

SCALAR

(0X351f00) 5

0x305108 0x351f00

$a = \$b;

A reference of a variable can be got when a backslash is put infront of it.

The address in memory is a scalar, so it can be assigned to one


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Creating a Reference Continued...

This address can be used to alter information at thatlocation

$b$aSCALAR

(0X351f00)3

0x305108 0x351f00

$$a = 3;

print $$a $b;

3 3


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Where can it be used?

References are used to

create multidimensional arrays/structures

pass complex data types to subroutines


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References

Reference Assignment How to Dereference

$refScalar = \$scalar; ${$refScalar} is a scalar value.

$refArray = \@array; @{$refArray} is an array value.

$refHash = \%hash; %{$refHash} is a hash value.

$refFunction = \&function; &{$refFunction} is a function location.


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2

File Handle


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Example

$file=C:\\file1.txt;

if (-e $file)

{

$size= -s $file;

print $size , " bytes \n";if (-z $file)

{

print" There is no data in $file \n";

}

}


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FILE Handling

A file is opened using open function

To read

open(FILE_HANDLE, file-path\\filename) or warn Can not open filename: $!;

To create\overwrite

open(FILE_HANDLE, >file-path\\filename) or die Can not create filename: $!;

To append

open(FILE_HANDLE, >>$filename) or die Can not append $filename: $!;

To read and write

open(FILE_HANDLE, +>$filename) or die Can not read-write $filename: $!;

To close an open file

close FILE_HANDLE;


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FILE Handling Contd

Reading from a fileSyntax

open(INFO, ">$file"); # Open for output

Example:

open(F,"test.pl");

while()

{print $_;

}

close F;


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FILE Handling Contd

SeekSyntax

seek FILEHANDLE, POSITION, OPTION

Exampleopen FILE,"C:\\file1.txt" or die "oops: $!";

seek FILE,10,0;

@line = ;

print @line;close(FILE);


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FILE Handling Contd

Writing into a fileSyntax

open(INFO, >$file); # Open for input

Example

open FILE,>C:\\file1.txt" or die "oops: $!";

print FILE Hello world;

close (FILE);


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Reading and Writing into a file Contd

Appending the data into a fileSyntax

open(INFO, ">>$file"); # Open for appending

Exampleopen FILE,>>C:\\file1.txt" or die "oops: $!";

print FILE Hello world;close (FILE);


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FILE Handling Contd

Close fileSyntax

Close ()

Example

open FILE,"C:\\file1.txt" or die "oops: $!";

close(FILE);


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