Just a slightly different way of writing it:

use File::Find;
finddepth sub {
  my $old = $_;
  return unless -f and s/\.abc$/.def/;
  warn("won't overwrite existing file at $File::Find::name"), return
    if -e;
  rename $old, $_ or warn "Cannot rename $old to $_ in $File::Find::di
+r: $!";
}, ".";
[download]

This works even if you rename a directory, because the directory gets renamed last.

-- Randal L. Schwartz, Perl hacker