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

die "Usage: $0 directory_path\n" unless ( @ARGV == 1 and -d $ARGV[0] );
my $target_dir = shift;
chdir $target_dir or die "chdir $target_dir: $!\n";

opendir( my $dir, "." );
my %files = map { $_ => -M } grep /\w/, readdir( $dir );
my @bacs = sort { $files{$a} <=> $files{$b} } grep /\.bac$/, keys %files;
@bacs or die "No *.bac file found in $target_dir - nothing to do\n";

my $latest_bac_age = $files{$bacs[0]};
( my $latest_bac_id = $bacs[0] ) =~ s/^(\w+).*/$1/;
warn "latest bac file in $target_dir is $bacs[0]\n";

for my $f ( keys %files ) {
    my $result = "kept";
    if ( $files{$f} > $latest_bac_age and $f !~ /^$latest_bac_id/ and -f $f ) {
        unlink $f and $result = "deleted";
    }
    warn "$result $f\n";
}