The system is from like 2013 and still going, but I really wish I could rewrite it in a language I can actually train people on in a reasonable amount of time. It took the one junior I have about 6 months to get to the point where he could read the syntax without tearing his hair out. It's not really built to create maintainable structures.
The libraries and stuff are full of opinionated little "gotchas." As an example, the Test::Simple module will throw errors if you use a number to title a test which is infuriating when you're writing a test which tests all the numbers in the space of acceptable or possible inputs.
Especially for example how variables have symbols for different types ($ for scalars, % for hashes, @ for arrays). And if you want to for example pass an array to a function you have to send it manually referenced with like method(\@myArray) which then inside the method is contained in a $scalar.
Compared to Python for example where you'd literally just pass the array to the method like method(array).
The values in @_ are aliased to the values in the subroutine call.
Most of the time, you want pass by value semantics, so you unpack the array and copy the values into function variables. If you want to modify an argument, it's typically passed in as a reference, and you can mess with it that way.
However, there are times when it would be horribly inefficient to make those copies, or when you need to do some magic (generally best avoided in 99.999% of your code), that this makes possible.
Also, since Perl functions are always variadic, it means that it's easy to work with a variable list of arguments in a function. For example, if you are expecting a list of key value pairs for your function, you can simply write:
my %args = @_
sub method {
my ($self, $a, $b, $c) = @_;
}
How does one tell Python to pass the contents of said array as distinct parameters to the function, instead of as a lone array parameter?
In Perl, that's the difference between foo(@bar) and foo(\@bar) or foo(1, 2, 3) vs foo([1, 2, 3]).
To quote myself from a recent discussion:
I think some languages do make it easy to write convoluted code, but through judicious use of coding standards (including a helping of common sense [don't be clever where you can at all avoid it, which IME is ~~almost~~ all the time], code linters, and so on) I think how you use a language plays a huge part in code maintainability.
For instance, I've heard PHP get shit on pretty badly all around the web, but I've worked at PHP shops that had nice, clean codebases, and my current Perl codebase is, in many ways, nicely structured. That's not to say there aren't some hairy codepaths that could use refactoring, but I really think that kind of thing, again, can happen in almost any language.