The sub keyword

The sub keyword defines a subroutine. Without a BLOCK, it is a forward declaration. By an assignment larger or shorter than LENGTH, the string will grow or shrink respectively to accommodate it. Without NAME, it defines an anonymous function, but returns the CODE ref of the just created closure.

  sub NAME BLOCK
  sub NAME (PROTO) BLOCK
  sub NAME : ATTRIBUTES BLOCK
  sub NAME (PROTO) : ATTRIBUTES BLOCK

sub { $x = 1; };
sub sam { ... };