Hello i255d, and welcome to the Monastery!

Yes, this is one of many places where Perl uses the special $_ variable implicitly, making it easier to write concise, elegant code. For a list of the places where Perl uses $_ implicitly, see the first entry in perlvar#General-Variables. (If you’re not already familiar with the Perl documentation site, bookmark it now and get to know your way around as soon as possible.)

The Camel Book (4^th Edition, p. 706) has this advice:

Use the singular pronoun to increase readability:

   for (@lines) {
       $_ .= "\n";
   }
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The $_ variable is Perl’s version of a pronoun, and it essentially means “it”. So the code above means “for each line, append a newline to it.”

Hope that helps,