SQL::Abstract can help greatly with this kind of thing.

use SQL::Abstract;

my @user = qw( ABCDEF01 HIJKL678 VWXYZ123H );
my @like = map { substr($_,0,4) . "%" } @user;

my $sql = SQL::Abstract->new;

my ( $statement, @bind ) = $sql->select("User",
                                  "*",
                                  { -or => { username => { LIKE => \@l
+ike } } });

print $statement, $/;
print join(", ", @bind), $/;

# Then some variation upon:
$dbh->prepare($statement)->execute(@bind);

__END__
SELECT * FROM User WHERE ( ( username LIKE ? OR username LIKE ? OR use
+rname LIKE ? ) )
ABCD%, HIJK%, VWXY%
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