I like this, but in the version I just added to my toolbox I made one small change: die if there's nothing to replace in @ARGV. Otherwise this script just sits there waiting for STDIN. Being not all that wise about the diamond operator it took me a while to figure out what was going on.

  my @starters = @ARGV ? @ARGV : ('./beginning_includes'); #current di
+rectory
  @ARGV = ();
  find sub {
    push @ARGV, $File::Find::name if $File::Find::name =~ /.txt$/i; # 
+or whatever condition here
  }, @starters;
  die "nothing to replace" unless @ARGV;
}
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