For a guess, you're wondering (did you forget to ask a question?) why this won't compile.

use strict;
use Fcntl ':flock';
#792341

my ($mday,$mon,$year) = (localtime(time))[3,4,5];
$year=$year+1900;

if ($mday < 10) {
    $mday = "0$mday"; 
} 
if ($mon < 10) {
    $mon = "0$mon";
} 
my $month = ++$mon;
my $date = "$mday.$month.$year";

my $file = "counter.txt";
my $host = $ENV{'REMOTE_HOST'};
my $ip = $ENV{'REMOTE_ADDR'};

my ($uq,@counter,@counter_data);

open(COUNTER, "$file") || &error("cannot open file for read");
@counter = <COUNTER>;
close(COUNTER);

for(@counter) { 
    chomp;
     @counter_data = split (/\|/, $_);
     if ($counter_data[0] eq $date && $counter_data1 eq $ip && $counte
+r_d +ata2 eq $host) { 
        $uq = 1;
     } 
} 
if (!$uq) { open (COUNTER, ">>$file") || &error("cannot open file for 
+write");
    flock (COUNTER, 2);
     print COUNTER "$date|$ip|$host\n" or die;
     close(COUNTER) or die;
} 

sub error { 
    my $error = $_[0];
    print "$error\n";
    exit;
}
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Some answers, found with perl -c 792341.pl

Global symbol "$counter_data1" requires explicit package name at 79234
+1.pl line 30.
Global symbol "$counter_d" requires explicit package name at 792341.pl
+ line 30.
Bareword "ata2" not allowed while "strict subs" in use at 792341.pl li
+ne 30.
792341.pl had compilation errors.
[download]

Please see Writeup Formatting Tips and Markup in the Monastery.

And it wouldn't hurt to include use warnings; along with strict.

Update: Missed the missing "[...]". Corrected that and the error messages