Perl - File I/O

Open Function

Following is the syntax to open file.txt in read-only mode. Here less than < sign 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") or die "Couldn't open file file.txt, $!";

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

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

open(DATA, ">file.txt") or die "Couldn't open file 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"); or die "Couldn't open file 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 the 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 the 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