Any time you find yourself making an ordered series of scalars, for example: $item_1, $item_2, ... you should consider using an array.

If you store your major, minor, and revision elements in an array you can operate on them as a group.

use strict;      # always 
use warnings;    # always
use diagnostics; # a pretty good idea

# Since I chose to use a couple of arrays to hold my 
# version info and update status, I'll make some 
# constants to make accessing them more hashlike.
use constant MAJOR => 0;
use constant MINOR => 1;
use constant REV   => 2;
use constant KEYWORDS         => qw( major  minor  revision );
use constant VERSION_ELEMENTS =>   ( MAJOR, MINOR, REV      );

# test data
my $old_version = '8.3.1';
my $new_version = '9.3.1';

# get an array with true values that indicate changes. 
my @updated = compare_versions( $old_version, $new_version );

# break new version string into an array
my @new_version = split_version( $new_version );

# Generate a list of commands to print
# If you have other processing to do as you make 
# your command list a foreach loop may make more sense
# than using map.
my @commands = map {
    $updated[$_]            # did we update this field?
    ? update_aht_command(   # if so, generate a command
        (KEYWORDS)[$_], 
        $new_version[$_], 
        "#DBVersion=$new_version",
      )
    : ();                   # otherwise put nothing in the command lis
+t. 
} VERSION_ELEMENTS;

print @commands;


# make version strings into arrays.
sub split_version {
    my $version = shift;
    return split /\./, $version;
}

# compare version strings.
# generate array of changes.
sub compare_versions {
    my $old = shift;
    my $new = shift;

    # convert version strings to arrays
    my @old = split_version($old);
    my @new = split_version($new);

    # handle a length mismatch.
    my $last = $#old > $#new ? $#old : $#new;

    # make a list with true values where changes have occurred.
    my @updated = map { $old[$_] != $new[$_] } (0..$last);

    # return the list.
    return @updated;
}

sub update_aht_command {
    my $keyword   = shift;
    my $new_value = shift;
    my $comment   = shift;

    return join '',
        "Update aht set $keyword = $new_value", 
        defined $comment 
            ? ( "\t"x3, $comment )
            : ( )
        ,"\n";
}
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Based on what I see in your sample code, I'd suggest you take a look at print, printf, and the qoute and quote-like operators section of perlop. Reading map should help with understanding my solution.