What are Perl 4, Perl 5, or Perl 6?

In short, Perl 4 is the parent to both Perl 5 and Perl 6. Perl 5 is the older sibling, and though they are different languages, someone who knows one will spot many similarities in the other.

The number after Perl (i.e. the 5 after Perl 5) is the major release of the perl interpreter as well as the version of the language. Each major version has significant differences that earlier versions cannot support.

The current major release of Perl is Perl 5, first released in 1994. It can run scripts from the previous major release, Perl 4 (March 1991), but has significant differences.

Perl 6 is a reinvention of Perl, it is a language in the same lineage but not compatible. The two are complementary, not mutually exclusive. Perl 6 is not meant to replace Perl 5, and vice versa. See "What is Perl 6?" below to find out more.