P5-lexical-underscore

Access lexical underscore of your caller

Starting with Perl 5.10, it is possible to create a lexical version of the Perl default variable $. Certain Perl constructs like the given keyword automatically use a lexical $ rather than the global $_.

It is occasionallly useful for a sub to be able to access its caller’s $_ variable regardless of whether it was lexical or not. The _ sub prototype is the official way to do so, however there are sometimes disadvantages to this; in particular it can only appear as the final required argument in a prototype, and there is no way of the sub differentiating between an explicitly passed argument and $_.

The lexicalunderscore function returns a scalar reference to either a lexical $_ variable somewhere up the call stack using PadWalker magic, or to the global $_ if there was no lexical version.

Wrapping lexicalunderscore in $ … dereferences the scalar reference, allowing you to access and even assign to it.