That's why you don't use bareword filehandles.

use strict;
use warnings;
use 5.010;


#Create some text files:

my @fnames = ('test1.txt', 'test2.txt');

for my $fname(@fnames) {
    open my $OUT, '>', $fname
        or die "Couldn't open $fname: $!";

    for my $num (1 .. 10) {
        say $OUT "$fname -- $num";
    }
}

#------------------

sub print_error {
    say 'error';
}

#------------------

#Read the text files:

FOR: 
for my $fname('test1.txt', 'test2.txt') {
    open my $INPUT, '<', $fname 
        or print_error();

    while(my $line = <$INPUT>) {
        print $line;
    }

    print "\n";
    
}

--output:--
test1.txt -- 1
test1.txt -- 2
test1.txt -- 3
test1.txt -- 4
test1.txt -- 5
test1.txt -- 6
test1.txt -- 7
test1.txt -- 8
test1.txt -- 9
test1.txt -- 10

test2.txt -- 1
test2.txt -- 2
test2.txt -- 3
test2.txt -- 4
test2.txt -- 5
test2.txt -- 6
test2.txt -- 7
test2.txt -- 8
test2.txt -- 9
test2.txt -- 10
[download]

When the input line operator, <>, reads end-of-file, it returns a false value that causes the while loop to end.

How about using the 3-arg form of open()?

open(DB,"<$F")

#compare to:

open my $INFILE, '<', $fname
  or die "Couldn't open $fname: $!"
[download]

How about printing out the filename in the loop?

Sorry, I misguded all of you and myself.

I blamed the filehandle handling for that behaviour, but it has nothing to do with the problem, at least not that filehandle, problem is about the STDOUT, in fact I tested the code through the shell awaiting for some print on STDOUT during the cicle, but due to a long operation inside the loop the unflushed output gave me NO feedback; setting the $|=1; give me each cicle outpup in real time...

however, thanks to all readers

On the other hand now I have the problem about unexpected slownees of the following code: (don't care about reply, I only post it here for completness, but more rightly I'll possibly send a new specific post for it)

$DB_STATS{COMB} is an hash of about other 180000 hashes each one with 2 keys, {Rit} and {Usc}. (COMB keys {$C} are of about 20-25 bytes)

foreach my $C( keys(%{$DB_STATS{COMB}}) ) { 
    $DB_STATS{COMB}{$C}{Rit}++; 
}
[download]

$DB_STATS{COMB} is an hash of about other 180000 hashes each one with 2 keys, {Rit} and {Usc}. (COMB keys {$C} are of about 20-25 bytes)

Could you post the first 10 lines produced by:

use Data::Dumper;

...
dumper( \%DB_STATS );
[download]

?

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

Copy your working file, and start deleting as much code as possible, until you're left with very short program, which demonstrates the bug, as per How do I post a question effectively?

Longshot, see DB and perldebguts

Thank you for your advices I'll profit them... I really know not much on perl debugging tools...

( how you could imagine I only posted that to restrict the scope of the problem to some notionism I could be missing, in the aim to reduce efforts and time spent by the interested monks on that problem )

Thank you all again!

No, they are pure text files; however I discover the problem, but I didn't understand what you mean and its purpose... I'll be interested if you'll explain it.

Thank you