If you don't specify an array for shift and pop to operate on, then they operate on @_ (or if used outside a sub definition, they operate on @ARGV).

# Which means that this...
sub read_shx_header {shift()->read_shx_shp_header('shx',@_);}

# Is a shortcut for writing out...
sub read_shx_header {
   my $self = shift @_;
   $self->read_shx_shp_header('shx', @_);
}
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