I would recommend avoiding eval for security reasons. It sounds like a simple substitution will do the trick. For example:

my $first_name = "foo";
my $last_name = "bar";

my $string = 'Dear $first_name, $last_name; Blah.';

$string =~ s/\$first_name/$first_name/g;
$string =~ s/\$last_name/$last_name/g;

#or
#$string =~ s/(\$\w+)/$1/eeg;
#if you are sure all variables in the text will exist.

print $string;
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-driver8