Here's a very straightforward solution. Instead of %, it uses _ as the escape character, since I think _ should be safe just about anywhere. (If not, maybe -?)

Anyway, my thinking is, escape almost everything (including the escape character, of course). :) 

sub encode_title {
  my($title) = @_;

  $title =~ s/([^A-Za-z0-9])/sprintf '_%02X', ord $1/ge;

  return $title;
}

sub decode_title {
  my($title) = @_;

  if ($title =~ /[^A-Za-z0-9_]/ or
      $title =~ /_(?![A-F0-9]{2})/) {
    return undef;
  }

  $title =~ s/_(..)/chr hex $1/ge;

  return $title;
}

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In reply to Re: Portably transforming a string to a valid filename by chipmunk
in thread Portably transforming a string to a valid filename by Anonymous Monk

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