Question

I am Newbie to Perl script.

I want to do a read and write operation on a file. I will open a file in read and write mode (+<), and will write into a file. Now, I want read the file whatever I have written to it previously. Below is my code:

#!/usr/bin/perl

`touch file.txt`; #Create a file as opening the file in +< mode
open (OUTFILE, "+<file.txt") or die "Can't open file : $!";

print OUTFILE "Hello, welcome to File handling operations in perl\n"; #write into the file

$line = <OUTFILE>; #read from the file

print "$line\n"; #display the read contents.

When I am displaying the read contents it’s showing a blank line. But the file “file.txt” has the data

Hello, welcome to File handling operations in perl

Why am I not able to read the contents. Whether my code is wrong or am I missing something.

Answer 1

The problem is that your filehandle position is located after the line you have written. Use the seek function to move the “cursor” back to the top before reading again.

An example, with some extra comments:

#!/usr/bin/env perl

# use some recommended safeguards
use strict;
use warnings;

my $filename = 'file.txt';
`touch $filename`;

# use indirect filehandle, and 3 argument form of open
open (my $handle, "+<", $filename) or die "Can't open file $filename : $!";
# btw good job on checking open sucess!

print $handle "Hello, welcome to File handling operations in perl\n";

# seek back to the top of the file
seek $handle, 0, 0;

my $line = <$handle>;

print "$line\n";

If you will be doing lots of reading and writing you may want to try (and not everyone suggests it) using Tie::File which lets you treat a file like an array; line access by line number (newline written automatically).

#!/usr/bin/env perl

# use some recommended safeguards
use strict;
use warnings;

use Tie::File;

my $filename = 'file.txt';
tie my @file, 'Tie::File', $filename
  or die "Can't open/tie file $filename : $!";

# note file not emptied if it already exists

push @file, "Hello, welcome to File handling operations in perl";
push @file, "Some more stuff";

print "$file[0]\n";