#!usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my $num_viol = 'number of violation(s)';

my %hash;
while (<>) { # Read all files that provided through ARGV
    chomp;
    my @tmp = split / /, $_;
    my $first = unpack 'a', $tmp[0];
    if (exists $hash{$first}) {
	$hash{$first}{$num_viol} += $tmp[2];
	next;
    }
    $hash{$first}{$num_viol} = $tmp[2];
} continue {
    close ARGV if eof; # reset $. each file
}

my @final;
foreach my $violation (sort keys %hash) {
    push @final, join(' ',
		      $violation,
		      $num_viol,
		      $hash{$violation}{'number of violation(s)'});
}

print Dumper \@final;

__END__

$ perl test.pl in.txt
$VAR1 = [
          'A number of violation(s) 5',
          'B number of violation(s) 3'
        ];

__DATA__

A_01: xxxxxxxxxxxxxxxxxxxx......... 1 violation
A_02: xxxxxxxxxxxxxxxxxxxx......... 4 violations
B_02: xxxxxxxxxxxxxxxxxxxx......... 3 violations