From a logic-foundations perspective of programming languages, Perl makes absolutely no sense. Its semantics have no rhyme or reason. It is completely illogical.
I searched for a Perl language spec and found this on wikipedia.
There is no written specification or standard for the Perl language, and no plans to create one for the current version of Perl. There has only ever been one implementation of the interpreter. That interpreter, together with its functional tests, stands as a de facto specification of the language.This basically says to me that Perl was designed as much as English was designed. And indeed, Perl is compared to a natural language.
I searched further and found the Perl language reference. And the Perl syntax page describes semantics, not syntax at all. On that page, there are numerous occasions that explain a rule, explain how there are exceptions to the rule, and then warning you to "don't do that"! It points out other things you "probably shouldn't rely upon".
...But that's just it isn't it. Perl is illogical. But it is intuitive. If programming languages had a sex, Perl would be female.
Its intuitive semantics can be seen in conditionals. The following is from the Perl syntax page.
The numberWhat??! ...The only types that seem to exist in the core language are scalars, lists, hashes, and functions of arbitrary signature. References seem to be the only thing with an arrow kind.
0, the strings
'', the empty list
undefare all false in a boolean context. All other values are true. Negation of a true value by
notreturns a special false value. When evaluated as a string it is treated as '', but as a number, it is treated as
All of this starts to make sense when you read about how Perl is an analogy to natural languages. Most languages look at programs as machines. Perl looks at programs as novels. There's nothing wrong with either way; they're just different. In fact, this is exactly what makes Perl interesting.
The design of Perl seems to be that of a medium not for engineers, but for people who create works of art or works of literature.
One claimed benefit of its natural-language-ness is that you can learn as you go as there are many levels of acceptable competence. (Take my competence in English for example, using words like "natural-language-ness".) This results in there being many poorly-written Perl programs, and Perl advocates argue that the burden in creating well-written code is rightly put on the programmer, not the language designer. The alternative however, is that those incapable of writing beautiful code never even learn the language. Whether fortunately or not, a language will always be judged to a large extent by the programs written in it.
Dabbling in Haskell recently, I am definitely going to learn more Perl simply for the contrast, as trying different things leads to more patterns.