For the DBI case, the correct answer is definitely placeholders.
However, in the general case, consider Interpolation.
It's pretty nifty. It lets you define "arbitrary interpolation semantics".
From its man page:
For example, you can say
use Interpolation
money => \&commify_with_dollar_sign,
E => 'eval',
placename => 'ucwords';
And then you can write these:
print "3 + 4 = $E{3+4}";
# Prints ``3 + 4 = 7''
$SALARY = 57500;
print "The salary is $money{$SALARY}";
# Prints ``The salary is $57,500.00''
For your need, you could use this:
use vars qw/$dbh/;
use DBI;
$dbh = DBI->connect('baz', 'foo', 'bar', 'Oracle');
use Interpolation quoteit => sub { $dbh->quote(@_) };
print "select * from foo where bar = $quoteit{baz}";
Which is quite handy. Still, in your particular case, placeholders are better.