#!/usr/bin/perl -wT
use strict;
my %hash_one = ('string_one' => 0,
                'string_two' => 0,
                '[[[string_three' => 0,   # test special chars behavior
                'string_four' => 0,
                'string_five' => 0,
                'string_six' => 0,
                'string_seven' => 0);

# first, create an array ref, element 0 is a qr// of the key, and element 1 is the count:
for (keys %hash_one) {
  $hash_one{$_} = [qr/\Q$_\E/, 0];
}
# then walk the data, trying all the regexen:

# Replaced with <DATA> - blakem
# @ARGV = qw(file.txt);
# close ARGV;

while (<DATA>) {
  for my $key (keys %hash_one) {
    $hash_one{$key}[1]++ if $_ =~ $hash_one{$key}[0];
  }
}
# finally, replace the arrayref with just the count:
$_ = $_->[1] for values %hash_one; # works in perl 5.5 and greater

print "$_ => $hash_one{$_}\n" for keys %hash_one;

__DATA__
1 string_one
string_two
2 string_two
[[[string_three
[[[string_three
3 [[[string_three
string_four
string_four
string_four
4 string_four
doesn'tmatchanything