Line_1:Line_1_1
Line_2:Line_2_2
Line_3:Line_3_3
Line_4:Line_4_4

##</code><code>##

Line_5:Line_5_5
Line_6:Line_6_6

##</code><code>##

Line_7:Line_7_7
Line_8:Line_8_8
Line_9:Line_9_9
Line_10:Line_10_10

##</code><code>##

my $i = 0;
while (<>) { # read from @ARGV
    chomp;
    push @{ $value[$i++] }, /:([^:]+)/; # get timestamp
    $i = 0 if eof;
}

##</code><code>##

my $i = 0;
my $filecount = 0;
while (<>) { # read from @ARGV
    chomp;
    $value[$i++]->[$filecount] = /:([^:]+)/; # get timestamp
    if (eof) {
        $i = 0;
        ++$filecount;
    }
}

##</code><code>##

if (!exists $value[$line]->[$file]) {
  # no value assigned, there is a hole in the array
} else {
  # value assigned
}