This will do want you want:

$string = 'perl345';
$_ = $string;
chop;
chop;
chop; #!
$string = $_;
[download]

Unless I have the sense of your question reversed, in which case this will work:

$string = "perl345";
for( reverse split //, $string ){
  $newstring .= chop unless /[a-z]/
}

print scalar reverse $newstring;
[download]

;-)

$,=42;for(34,0,-3,9,-11,11,-17,7,-5){$*.=pack'c'=>$,+=$_}for(reverse s
+plit//=>$*
){$%++?$ %%2?push@C,$_,$":push@c,$_,$":(push@C,$_,$")&&push@c,$"}$C[$#
+C]=$/;($#C
>$#c)?($ c=\@C)&&($ C=\@c):($ c=\@c)&&($C=\@C);$%=$|;for(@$c){print$_^
+$$C[$%++]}
[download]