$text =~ s/[\x00-\x09\x0b-\x1f]+//g; # + for speed
# or
$text =~ tr/\x00-\x09\x0b-\x1f//d; # tr/// for even more speed

##</code><code>##

# OLD:$text =~ s/(?!\n)[^\x00-\x1f]//g;
$text =~ s/[^\x00-\x1f](?<!\n)//g; # (Can't use + now)

# or (if you need to exclude another character,
# let's say \n and \r

# OLD:$text =~ s/(?![\r\n])[^\x00-\x1f]//g;
$text =~ s/[^\x00-\x1f](?<![\r\n])//g;

# Note: it's usually better to avoid \r and \n and use
# literals like \cM and \cJ or \015, \012 or \x0d, \x0a.

##</code><code>##

2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$