What is a double underscore in Perl?

Question

I'm trying to understand someone else's Perl code without knowing much Perl myself. I would appreciate your help.

I've encountered a Perl function along these lines:

MyFunction($arg1,$arg2__size,$arg3)

Is there a meaning to the double-underscore syntax in $arg2, or is it just part of the name of the second argument?

Answer 1

There is no specific meaning to the use of a __ inside of a perl variable name. It's likely programmer preference, especially in the case that you've cited in your question. You can see more information about perl variable naming here.

Answer 2

As in most languages underscore is just part of an identifier; no special meaning.

But are you sure it's Perl? There aren't any sigils on the variables. Can you post more context?

Answer 3

As far as the interpreter is concerned, an underscore is just another character allowed in identifiers. It can be used as an alternative to concatenation or camel case to form multi-word identifiers.

A leading underscore is often used to mean an identifier is for local use only, e.g. for non-exported parts of a module. It's merely a convention; the interpreter doesn't care.