How can I count the number of times a pattern appears - perl

Question

I am trying to count the number of occurrences that a particular string appears in a text document so that the string can be deleted if it occurs less than 5 times. The text file has a list of dates that are formatted as 2015-06-16 07:40:00.
After processing the incoming data from 2015-06-16 07:40:00 to 2015061607, I want to count the number of times that this string appears. I have the processing of the incoming data correct but I don't know how to count the occurrences of the string.
This is what I have so far.
#!/usr/bin/perl
foreach $file (#ARGV) {
open (OUT, ">/d2/aschwa/scripts_and_programs/NST_Scripts/data_organizers/Filtered_$file") || die "Cannot open specified file\n";
open (RAW, "/d2/aschwa/scripts_and_programs/NST_Scripts/data_organizers/$file") || die "Cannot open specified file to be processed\n";
while(<RAW>) {
$event = $_;
chop($event);
#event = split (',', $event);
($date_time, $var1, $var2, $var3) = #event[(0,1,2,3)];
#date_time = split (' ', $date_time);
($date, $time) = #date_time[(0,1)];
#date_mod = split ('-', $date);
($year, $month, $day) = #date_mod[(0,1,2)];
#time = split (':', $time);
($hr, $mins, $sec) = #time[(0,1,2)];
$datehr = $year . $month . $day . $hr;
foreach ($event) {
$count{$datehr}++;
}
}
}

Answer 1

I think you should use a regular expression rather than repeated calls to split
This example reads through each file twice, counting the dates on the first pass and printing those lines whose dates appear more than five times on the second
It doesn't compress the date-time as you have done, but captures just up to the hour field, so the keys of the %count hash look like 2015-06-16 07. It is only extra code to remove the punctuation and isn't necessary to make the program work
I've also used autodie, which has been available since v5.10 of Perl and automatically checks the status of open and chdir calls for you. It is also best practice to use lexical file handles and the three-parameter form of open
#!/usr/bin/perl
use strict;
use warnings;
use 5.010;
use autodie;
use constant DIR => '/d2/aschwa/scripts_and_programs/NST_Scripts/data_organizers';
chdir DIR;
for my $file ( #ARGV ) {
open my $raw_fh, '<', $file;
my %count;
while ( <$raw_fh> ) {
++$count{$1} if /^(\d\d\d\d-\d\d-\d\d \d\d):\d\d:\d\d/;
}
seek $raw_fh, 0, 0; # Rewind input file
open my $out_fh, '>', "Filtered_$file";
while ( <$raw_fh> ) {
print unless /^(\d\d\d\d-\d\d-\d\d \d\d):\d\d:\d\d/ and $count{$1} < 5;
}
}