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

open my $fh, '<', 'file1.csv' or die $!;

my ($actDt, $inactDt, $count) = ('', '', 0);
my $previous_key = '';

while (<$fh>) {
    chomp;
    my ($a1, $b1, $begin, $end) = split /,/;
    my $key = "$a1,$b1";
    
    if ($previous_key eq $key) {
        $inactDt = $end;
        $count++;
    }
    else { # either reached the end of a record or this is the first record
        print join(",", $previous_key, $actDt, $inactDt), "\n"
            if $count > 1;
        $actDt = $begin;
        $inactDt = $end;
        $count = 1;
    }
    $previous_key = $key;
}

print join(",", $previous_key, $actDt, $inactDt), "\n"
    if $count > 1;