use strict;
use warnings;
use Data::Dumper;

my $string_exp = 'something in this string is a number. ${=NumberFormat "99999999"} is a number. And another ${=CharFormat "X*"} is ${=NumberFormat "9+"}.';
my @pieces = split /(\$\{.*?\})/, $string_exp;

print Dumper \@pieces;

##</code><code>##

$VAR1 = [
          'something in this string is a number. ',
          '${=NumberFormat "99999999"}',
          ' is a number. And another ',
          '${=CharFormat "X*"}',
          ' is ',
          '${=NumberFormat "9+"}',
          '.'
        ];

##</code><code>##

$VAR1 = [
          'something in this string is a number. ',
          '${=NumberFormat "99999999"}',
          ' is a number. And another ',
          '${=CharFormat "X*"}',
          ' is $=NumberFormat "9+"}.'
        ];