#!/usr/bin/perl
use strict; use warnings;
use File::stat qw( stat );
use POSIX qw( strftime );
my %counts_by_date;
while(<>) {
    chomp;
    my $stat = stat($_) or do { warn("Can't stat \"$_\": $!\n"); next; };
    ++$counts_by_date{ strftime("%F", localtime($stat->mtime)) } if -f _;
}
printf "%s %s\n", $_, $counts_by_date for keys(%counts_by_date);