Perl File Handling

  • File handling is the most important part in any programming language. 
  • A Perl filehandle is a variable that associates with a file. 
  • Perl filehandles are capable of creating, reading, opening and closing a file.
  • Perl File handling is important as it is helpful in accessing file such as text files, log files or configuration files.
1) Open a file.

The open() function has three arguments:

  1. Filehandle: that associates with the file
  2. Mode: you can open a file for reading, writing or appending.
  3. Filename: the path to the file that is being opened.

To open a file in a specific mode, you need to pass the corresponding operand to the open() function.

 The open file modes are explained in details as follows:

  1. Read mode (<): you only can read the file but cannot change its content.
  2. Write mode (>): If the file does not exist, a new file is created. If the file already exists, the content of the file is wipe out, therefore, you should use the write mode with extra cautious.
  3. Append mode ( >>): You can open the file for appending new content to the existing content of the file. However, you cannot change the existing content in the file.
Example: 
open(FH, '<', 'c:\temp\test.txt');


The open file returns true on success and false on failure. You can use the die() function to handle a file-opening failure. 
open(FH, '<', 'c:\temp\test.txt') or die $!;
  • $! is a special variable that conveys the error message telling why the open() function failed. 
  • It could be something like “No such file or directory” or “Permission denied”. 
  • In case the file c:\temp\test.txt does not exist, you get an error message “No such file or directory”.
2) Close a File 
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#!/usr/bin/perl
use warnings;
use strict;

#Opening a file
open(FH, '<', 'c:\temp\test.txt');

#Closing a file
close(FH);

3) Read a file
To read from a file in read mode, you need to put the filehandle variable inside angle brackets as follows:

 To read the next line of the file:
$line = <FH>;

To read a file line by line to the end of the file:
while(<FH>){
}

 
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#!/usr/bin/perl
use warnings;
use strict;

#Opening a file
open(FH, '<', 'c:\temp\test.txt');

while(<FH>){
   print $_;
}

#Closing a file
close(FH);

4) Write a file
You should use the print() function to write data into file as follows:

print FH $str;

 Example of write file:
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#!/usr/bin/perl
use warnings;
use strict;
 
my $str = "This is the sample text!";
 
open(FH, '>', 'c:\temp\test.txt') or die $!;
 
print FH $str;

close(FH);

5) Perl Test Operator
  • Perl file test operators are used to check various characteristics of a file.
  • In order to perform read or write tasks, you use Perl file test operators to make sure the file is exist and readable.
  • The Perl file test operators are logical operators which return true or false.
Example: To check if file is exist, you have to use -e operator
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#!/usr/bin/perl
use warnings;
use strict;
 
my $filename = 'c:\temp\test.txt';

if(-e $filename){
   print("File exists\n");
}else{
   print("File does not exists\n");
}

The following list explains the most important Perl file test operators:

 -r: check if the file is readable
-w: check if the file is writable
-x: check if the file is executable
-e: check if the file exists.
-z: check if the file is empty.
-s: check if the file has nonzero size (returns size in bytes).
-f: check if the file is a plain file.
-d: check if the file is a directory.
-l: check if the file is a symbolic link.

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