/^\Q$host\E$/;
 ^ ^      ^^
 | |      ||
 | |      |+ - End of line
 | |      + - End quote metacharacters
 | + - Begin quote metacharacters (e.g., [.*\+], etc.)
 + - Match beginning at the start of the line

##</code><code>##

use warnings;
use strict;

my $host = 'db';

while (<DATA>) {
	print if /^\Q$host\E$/i;
}

__DATA__
db
db4323
dbwindows822.tp.com
db726.tp.com

##</code><code>##

db

##</code><code>##

db
db4323
dbwindows822.tp.com
db726.tp.com