Perl open Function

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Description

This function opens a file using the specified file handle. The file handle may be an expression, the resulting value is used as the handle. If no filename is specified a variable with the same name as the file handle used (this should be a scalar variable with a string value referring to the file name). The special file name '-' refers to STDIN and '>-' refers to STDOUT.

Syntax

Following is the simple syntax for this function:

open FILEHANDLE, EXPR, LIST

open FILEHANDLE, EXPR

open FILEHANDLE

Return Value

This function returns o on failure and 1 on success.

Example

Following is the syntax to open file.txt in read-only mode. Here less than < signe indicates that file has to be opend in read-only mode

open(DATA, "<file.txt");

Here DATA is the file handle which will be used to read the file. Here is the example which will open a file and will print its content over the screen.

#!/usr/bin/perl

open(DATA, "<file.txt");

while(<DATA>)
{
   print "$_";
}

Following is the syntax to open file.txt in writing mode. Here less than > signe indicates that file has to be opend in writing mode

open(DATA, ">file.txt");

This example actually truncates (empties) the file before opening it for writing, which may not be the desired effect. If you want to open a file for reading and writing, you can put a plus sign before the > or < characters.

For example, to open a file for updating without truncating it:

open(DATA, "+<file.txt");

To truncate the file first:

open DATA, "+>file.txt" or die "Couldn't open file file.txt, $!";

You can open a file in append mode. In this mode writing point will be set to the end of the file

open(DATA,">>file.txt") || die "Couldn't open file file.txt, $!";

A double >> opens the file for appending, placing the file pointer at the end, so that you can immediately start appending information. However, you can.t read from it unless you also place a plus sign in front of it:

open(DATA,"+>>file.txt") || die "Couldn't open file file.txt, $!";

Following is the table which gives possible values of different modes

Entities	Definition
< or r		Read Only Access
> or w		Creates, Writes, and Truncates
>> or a		Writes, Appends, and Creates
+< or r+	Reads and Writes
+> or w+	Reads, Writes, Creates, and Truncates
+>> or a+	Reads, Writes, Appends, and Creates


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