{
    my $foo = 'ABC-2N322-850103';
    sub prefix () :lvalue {
        substr $foo, 0, index( $foo, '-')
    }
}

##</code><code>##

{
    my $foo = 'ABC-2N322-850103';
    sub prefix () :lvalue {
        substr $foo, 0, index( $foo, '-')
    }
    sub foo () { $foo }
}
print foo, $/;
my $bar = prefix = 'DEFG';
print $bar, $/
print foo, $/;
__END__
output:
ABC-2N322-850103
DEF
DEFG-2N322-850103