$re = "\.";

foreach (qw( . a )) {
   print("$_ ", /$re/ ? "matches" : "doesn't match", " $re\n");
}

$re = qr/\./;

foreach (qw( . a )) {
   print("$_ ", /$re/ ? "matches" : "doesn't match", " $re\n");
}

##</code><code>##

. matches .
a matches .
. matches (?-xism:\.)
a doesn't match (?-xism:\.)

##</code><code>##

$var = '...';
$re = qr/abc\Q$var\Eghi/;

foreach (qw(
   abcdefghi
   abc...ghi
)) {
   print("$_ ", /$re/ ? "matches" : "doesn't match", "\n");
}

##</code><code>##

abcdefghi doesn't match
abc...ghi matches