use strict;
use warnings;

my $foo ="some hello message";

my ($hello) = $foo =~ /(hello)/;
$hello //= ''; # null string if "hello" was not found

__END__
$hello will be either "hello" or 
a null string. Better than an undef value.
Amongst other things, this maintains a 
"printable value" for $hello.

use $hello in a Boolean context.

$foo is a string. Do not reuse that string
variable name to mean something different.
Create new Boolean variable.
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