apt-downgrade-all-packages.pl

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

$ENV{LC_ALL} = 'C';

my $need_downgrade = `dpkg -l | grep ^i | awk '{print \$2}'`;
$need_downgrade =~ s/^\s+|\s+$//g;

my @final_cmd = ("sudo", "apt-get", "install", "--allow-downgrades", "--allow-change-held-packages", "--reinstall");

for my $pkg (split("\n", $need_downgrade)) {
	my $cache_info = `apt-cache policy '$pkg'`;
	
	my @versions;
	while ($cache_info =~ /^( \*\*\* |     )(\S+) (\d+)$/img) {
		push @versions, {v => $2, p => int $3};
	}
	
	my ($installed_version) = $cache_info =~ /^  Installed: (.*?)$/m;
	die $cache_info if !$installed_version;
	
	@versions = sort { $b->{p} <=> $a->{p} } @versions;
	
	if (@versions >= 2 && $versions[0]->{v} ne $installed_version) {
		print "$pkg $installed_version -> ".$versions[0]->{v}."\n";
		push @final_cmd, "$pkg=".$versions[0]->{v};
	}
}

print "\n\n";
print join(" ", @final_cmd)."\n";