It will last at least until Perl6 comes out
A few (obvious) points:
- Perl 6 isn't currently out. It may not be for a very long time, and it may change to be more perl5ish.
- Once Perl 6 comes out, Perl 5 isn't going anywhere. People will still develop new applications with it, old ones will have to be maintained, etc.
- Learning a specific language that is considered obsolete isn't a bad thing. Learning COBOL can teach you wonders about good language design ;-)
Your general rule is fairly effective though, most overly specific books I pass on after about a year.
