I have tried a few methods unsuccessfully
You should have shown us those attempts, so we could help you understand why they failed, and how to improve them.

Anyway, a rather simple and straightforward solution to your problem, is to turn your code into a function: 

sub process_file
{
  my ($original, $final) = @_;

  open( my $original_fh, "<", $original ) or die $!;
  open( my $final_fh,    ">", $final )    or die $!;

  my $first = <$original_fh>;
  print $final_fh $first;
  my @replace = $first =~ /"([^"]*)"/g;

  while (my $line = <$original_fh>) {
    print "Enter the desired number of columns: ";
          my $nr = <STDIN>;
          chomp($nr);
    $line =~ s/((\w\w\t){$nr})/$1\n/g;
    $line =~ s/\t/,/g;
    $line =~ s/(\d{2})/$replace[$1]/g;
    print $final_fh $line;
  }

  close $original_fh;
  close $final_fh;
}

[download]
And call that function on all your files (process_file("A.txt", "B.csv");).

You can get the list of files using glob ; this will return the list of files that match a given pattern: my @files = glob 'path/*.txt'; If you don't provide a path, glob will look into the current directory, which you can change with chdir.

And to change the extension, you can just use a substitution: my $new_file = $name =~ s/txt$/csv/r;

Edit: changed the last sentence, Akatsuki obviously already knows about substitutions.

In reply to Re: Read from multiple files change the data with a script and the write the respective output files with a different extension by Eily
in thread Read from multiple files change the data with a script and the write the respective output files with a different extension by Akatsuki

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