<DATA> prevents foreach loop from being executed, why? :) - perl

Question

I have two nested foreach loops. If I use this code:
foreach (#directories) {
my $actual_directory = $_;
print "\nactual directory: ".$actual_directory."\n";
foreach (#files) {
my $file_name = $_;
my $actual_file = $actual_directory.$file_name;
print $actual_file."\n";
open(DATA, $actual_file) or die "Nelze otevřít zdrojový soubor: $!\n";
my $line_number = 0;
# while (<DATA>){
# my #znaky = split(' ',$_);
# my $poradi = $znaky[0]; #poradi nukleotidu
# my $hodnota = $znaky[1]; #hodnota
# my #temp = $files_to_sum_of_lines{$actual_file};
# $temp[$line_number] += $hodnota;
# $files_to_sum_of_lines{$actual_file} = #temp;
# $line_number+=1;
# }
# close(DATA);
}
}
I got this output:
actual directory: /home/n/Plocha/counting_files/1/
/home/n/Plocha/counting_files/1/a.txt
/home/n/Plocha/counting_files/1/b.txt
actual directory: /home/n/Plocha/counting_files/2/
/home/n/Plocha/counting_files/2/a.txt
/home/n/Plocha/counting_files/2/b.txt
However, if I uncomment "while (<DATA>){ }", I loose a.txt and b.txt, so the output looks like this:
actual directory: /home/n/Plocha/counting_files/1/
/home/n/Plocha/counting_files/1/a.txt
/home/n/Plocha/counting_files/1/b.txt
actual directory: /home/n/Plocha/counting_files/2/
/home/n/Plocha/counting_files/2/
/home/n/Plocha/counting_files/2/
How can this while (<DATA>) prevent my foreach from being executed?
Any help will be appreciated. Thanks a lot.

Answer 1

In addition to not using DATA, try using lexical loop variables, and lexical filehandles. Also, Perl's built-in $. keeps track of line numbers for you.
for my $actual_directory (#directories) {
print "\nactual directory: ".$actual_directory."\n";
foreach my $file_name (#files) {
my $actual_file = $actual_directory.$file_name;
print $actual_file."\n";
open my $INPUT, '<', $actual_file
or die "Nelze otevřít zdrojový soubor: $!\n";
while (my $line = <$INPUT>) {
my #znaky = split(' ', $line);
my $poradi = $znaky[0]; #poradi nukleotidu
my $hodnota = $znaky[1]; #hodnota
#temp = $files_to_sum_of_lines{$actual_file};
$temp[ $. ] += $hodnota;
$files_to_sum_of_lines{$actual_file} = #temp;
}
close $INPUT;
}
}
On the other hand, I can't quite tell if there is a logic error in there. Something like the following might be useful:
#!/usr/bin/perl
use warnings; use strict;
use Carp;
use File::Find;
use File::Spec::Functions qw( catfile canonpath );
my %counts;
find(\&count_lines_in_files, #ARGV);
for my $dir (sort keys %counts) {
print "$dir\n";
my $dircounts = $counts{ $dir };
for my $file (sort keys %{ $dircounts }) {
printf "\t%s: %d\n", $file, $dircounts->{ $file };
}
}
sub count_lines_in_files {
my $file = canonpath $_;
my $dir = canonpath $File::Find::dir;
my $path = canonpath $File::Find::name;
return unless -f $path;
$counts{ $dir }{ $file } = count_lines_in_file($path);
}
sub count_lines_in_file {
my ($path) = #_;
my $ret = open my $fh, '<', $path;
unless ($ret) {
carp "Cannot open '$path': $!";
return;
}
1 while <$fh>;
my $n_lines = $.;
close $fh
or croak "Cannot close '$path': $!";
return $n_lines;
}

Answer 2

Perl uses __DATA__ to make a pseudo-data file at the end of the package. You can access that using the filehandle DATA, e.g. <DATA>. Is it possible that your filehandle is conflicting? Try changing the filehandle to something else and see if it works better.