Hi, lalalala1, and welcome to PerlMonks!

Excellent suggestions above. The following incorporates almost all of them, and avoids a collision with the output file by grepping the glob (sounds like a horror movie title...).

It opens each text file for the data you need, and that data is pushed onto an array that's written out to the output file:

use strict;
use warnings;

my $outFile = 'extractedData.txt';
my @sampleLines;

for my $file ( grep !/^\Q$outFile\E$/, <*.txt> ) {
    open my $fh, '<', $file or die $!;

    # Get data from file...
    push @sampleLines, $data;

    close $fh;
}

open my $outFH, '>', $outFile or die $!;
print $outFH @sampleLines;
close $outFH
[download]

I know that this is more than you requested, but I hope it's helpful.