$one = substr($in, 23, 15);
$two = substr($in, 28, 10);

##</code><code>##

$ perl -we'sub foo { print $_[0] } eval { foo(substr "abc", 4, 1); 1} or die "croak: $@"'
croak: substr outside of string at -e line 1.

##</code><code>##

$in =~ /^  (?=.{23}(.{15}))   # field one
           (?=.{28}(.{10}))   # field two
       /xs
   or warn "bad input: $in ";