This kind of question comes up a lot, not just about Perl, but about Ruby, Cobol, PHP, Java, Haskell, etc. Unfortunately, it doesn't really have an answer for two reasons.
Firstly, the popularity of a language in no way predicts your potential future earnings if you learn that language. PHP is probably the world's most widely used language, yet the average salary for a PHP developer is lower. I found learning VBA immensely useful, but it was a frustrating language to use. I love using Ruby and Python, but PHP work is much easier to find. Ruby taught me a lot about programming, so it was definitely worth learning.
Secondly, developers are not good or bad because of the language they use, but because of the value they provide. You could be a shockingly bad developer, but excellent at explaining difficult concepts in VisualBasic to the rich and powerful - you'll probably get rich.
Essentially, you need to reframe your question, and then answer it yourself. What are you hoping to get out of programming? Do you want to be rich? Do you enjoy solving problems? Are you happy to work every hour of the day, or do you want to get out at 5pm every night? Which areas of programming make you feel most comfortable - writing CRUD apps or complex algorithms? Do you have any types of company you would refuse to work for (say gambling or finance)? Are you an extrovert or an introvert? Do you prefer to work in a small company or a large corporate? These kinds of questions will narrow your choices and help you to choose a career path.
So... you might learn Perl, which causes you to get a job you end up hating but introduces you to somebody that recommends you learn Haskell, which gets you the job you love for gazillions per year. In other words, how the $%&# should we know?
Perl has been around for a long time. Given its popularity as a language used for simple web services and system administration there has been a lot of code written. A lot of code written also means there's a lot of code to maintain.
When it comes to programming you should pick a language you are comfortable with and use it often. Once you have mastered simple programming methodologies, moving between languages will be relatively easy.
If you want to learn something that's going to get you a job quicker, go to indeed.com or simplyhired.com and search the various languages in the job listings in your local area or where you want to work. You'll get a better gauge of what hiring managers are looking for.
i check dice, indeed and simplyhired and openings are pop up alot, but its hard to tell with HR people posting the Jobs and they know nothing about the field.
i'll defer to alan perlis on this: "a language that doesn't affect the way you think about programming, is not worth knowing."
does perl offer something distinctly different from other, younger languages? IMHO, not really.
there is a bunch of perl code out there that needs maintenance, which is why i learned just enough perl to read it. but who truly gets into programming to maintain something that's already built? might as well learn COBOL if that's how you think.
Perl 6, a new language inspired by Perl, is coming. ;)
IMO; Neither it or Perl 5 provide particular advantages as a general career path at this point...aside perhaps from getting out in front of Perl 6 on the chance it suddenly becomes the next big thing.
That's not to say Perl and Perl 6 are not worth knowing and using. I find The approach to errors in Perl 6 to look like an attractive future. But a lot of Perl's traditional strength in regular expressions appears in other languages. and I'm not sold on the idea that Perl's contextual evaluation semantics outweigh the textual complexity it introduces when reading source code.
[Ignoring that the methodology can be completely flawed ...]
It's difficult to estimate the errors without finding the complete dataset and being a statistician, but let's try anyway.
We can look at the lower curves and assume that they are wavy because of some noise error. The curves of the VB and Python (and close languages) go up and down between .5% and 1%, and that value is similar to the monthly change.
So my guess is that the noise for the languages in the lower part of the graph is close to 1%. Then a variation of .2% of Perl is not meaningful. Don't get too happy now, and if next month it goes down .3% don't get sad.
It really isn't coming back, and I hope it never does. Becoming a Perl expert is pretty career limiting, because you will need to learn another language at some point, and none of them are perl-like so you gain no advantage being a master with perl.
Firstly, the popularity of a language in no way predicts your potential future earnings if you learn that language. PHP is probably the world's most widely used language, yet the average salary for a PHP developer is lower. I found learning VBA immensely useful, but it was a frustrating language to use. I love using Ruby and Python, but PHP work is much easier to find. Ruby taught me a lot about programming, so it was definitely worth learning.
Secondly, developers are not good or bad because of the language they use, but because of the value they provide. You could be a shockingly bad developer, but excellent at explaining difficult concepts in VisualBasic to the rich and powerful - you'll probably get rich.
Essentially, you need to reframe your question, and then answer it yourself. What are you hoping to get out of programming? Do you want to be rich? Do you enjoy solving problems? Are you happy to work every hour of the day, or do you want to get out at 5pm every night? Which areas of programming make you feel most comfortable - writing CRUD apps or complex algorithms? Do you have any types of company you would refuse to work for (say gambling or finance)? Are you an extrovert or an introvert? Do you prefer to work in a small company or a large corporate? These kinds of questions will narrow your choices and help you to choose a career path.
So... you might learn Perl, which causes you to get a job you end up hating but introduces you to somebody that recommends you learn Haskell, which gets you the job you love for gazillions per year. In other words, how the $%&# should we know?