package Subst ; use Filter::Util::Call ; use Carp ; use strict ; use warnings ; sub import { croak("usage: use Subst qw(from to)") unless @_ == 3 ; my ($self, $from, $to) = @_ ; filter_add( sub { my ($status) ; s/$from/$to/ if ($status = filter_read()) > 0 ; $status ; }) } 1 ;