use strict;
use 5.020; # for best efficiency on $&

use Test::More tests => 11;

my $orig = 'This is a real number, 123456.56';
my $want = 'This is a real number, 493824.56';

(my $have = $orig) =~ s/\d+/sprintf "%i", 4 * $&/e;
my $intpart = $&;
is $intpart, 123456, 'int part captured';
is $have, $want, 'Multiply int part by 4';

($have = $intpart) =~ s/./3/g;
is $have, 333333, 'Int part digits set to "3" trivially, with /./';

($have = $intpart) =~ s/\d/3/g;
is $have, 333333, 'Int part digits set to "3" trivially, with /\\d/';

$want = 'This is a real number, 333333.56';
($have = $orig) =~ s/\d+/(my $int = $&) =~ s#.#3#g; $int/e;
is $have, $want, 'Replace int part in string with all 3s';

$want = 'This is a real number, 123,456.56';
($have = $orig) =~ s{ \d+ }{
    $& =~ s/ (?<=\d) (?= (?:\d{3} )+ (?!\d) ) /,/xrg; }ex;
$intpart = $&;
is $intpart, 123456, '$& int part captured';
is $have, $want, 'Insert commas where appropriate';

($have = $orig) =~ s{ (\d+) }{
    $1 =~ s/ (?<=\d) (?= (?:\d{3} )+ (?!\d) ) /,/xrg; }ex;
$intpart = $1;
is $intpart, 123456, '$1 int part captured';
is $have, $want, 'Insert commas where appropriate';

($have = $orig) =~ s{ (?<int> (\d+)) }{
    $+{int} =~ s/ (?<=\d) (?= (?:\d{3} )+ (?!\d) ) /,/xrg; }ex;
$intpart = $+{int};
is $intpart, 123456, '<int> part captured';
is $have, $want, 'Insert commas where appropriate';

exit(0);
__END__