man subs () - Perl pragma to predeclare sub names
NAME
subs - Perl pragma to predeclare sub names
SYNOPSIS
use subs qw(frob);
frob 3..10;
DESCRIPTION
This will predeclare all the subroutine whose names are in the list, allowing you to use them without parentheses even before they're declared.
Unlike pragmas that affect the CW$^H hints variable, the CWuse vars and CWuse subs declarations are not BLOCK-scoped. They are thus effective for the entire file in which they appear. You may not rescind such declarations with CWno vars or CWno subs.
See Pragmatic Modules in perlmodlib and strict subs in strict.