#!/usr/bin/perl
use strict;
use warnings;

my(@lines, $line);

print "\n\tUsing tr\n";

@lines = <DATA>;

for $line(@lines) {
  chomp $line;
  my $line1 = $line;
  if ( ($line1 =~ tr/[r|R]/r/) == 4 ) {   # Case insensitive
        print "$line1\n";
  }
}

print "\n\t using match:\n";
for $line(@lines) {
    if ( $line =~ /
           ^          # start at beginning of line
           ([^rR]*)   # 0 or more non-r chars
           r          # match "r"
           ([^rR]*)   # negative lookahead, 0 or more non-r chars
           r
           ([^rR]*)   # alternately, could be ?=[^r]*
           r
           ([^rR]*) 
           r
           ([^rR]*) 
           $          # end of line
           /ix) {     # extended syntax; end of match; end of condition
        print "$line\n"
    }
}
print "\n\t using match2:\n";
for $line(@lines) {
    if ( $line =~ /^([^r]*|[^R]*)r([^r]*|[^R]*)r([^r]*|[^R]*)r([^r]*|[^R]*)r([^r]*|[^R]*)$/i) {
        print "$line\n";
    }
}
print "\n and the data is:\n";
for $line(@lines) {
    print $line . "\n";
}
print "\nDone\n";


__DATA__
There are four "r"s in this sentence. 4
This one has how many? 0
None in this. 0
But where can there be as many words with 'r's as there are here? 7
Still, rrrr makes no sense. 4
Drill for sentences with multiple instances of "are" and "were" regularly. 5
There are four "r"s in this sentence. 4
This one has how many? 0
None in this. 0
But where can there be as many words with 'r's as there are here? 7
Still, rrrr makes no sense. 4
Drill for sentences with multiple instances of "are" and "were" regularly. 5
Argh. Right you are, Randy! 4 matches if insensitive (but only 2 match when case sensitive).

##</code><code>##

        Using tr
There are four "r"s in this sentence. 4
Still, rrrr makes no sense. 4
There are four "r"s in this sentence. 4
Still, rrrr makes no sense. 4
Argh. right you are, randy! 4 matches if insensitive but only 2 match when case sensitive.

         using match:
There are four "r"s in this sentence. 4
Still, rrrr makes no sense. 4
There are four "r"s in this sentence. 4
Still, rrrr makes no sense. 4
Argh. Right you are, Randy! 4 matches if insensitive but only 2 match when case sensitive.

         using match2:
There are four "r"s in this sentence. 4
Still, rrrr makes no sense. 4
There are four "r"s in this sentence. 4
Still, rrrr makes no sense. 4
Argh. Right you are, Randy! 4 matches if insensitive but only 2 match when case sensitive.

 and the data is: ....