#!/usr/bin/env perl

# matches-per-line - prefix lines with count of matches for given regex
#
# Usage:
#
#   echo 'RRR' | matches-per-line "R"
#   matches-per-line R ./example.txt

use warnings;
use strict;

my $pattern = shift @ARGV;

while (my $line = <>) {
  chomp $line;

  # Get a count of matching substrings:
  my @matches = $line =~ m/$pattern/g;
  my $count = scalar @matches;

  print "$count\t$line\n";
}