$ perl -we'
use Data::Dumper;
$Data::Dumper::Useqq = 1;
my $s = "foo bar   \n";
print Dumper $s;
$s =~ s/ {3}$//;
print Dumper $s;
'
$VAR1 = "foo bar   \n";
$VAR1 = "foo bar\n";
$ perl -we'
use Data::Dumper;
$Data::Dumper::Useqq = 1;
my $s = "foo bar   \r\n";
print Dumper $s;
$s =~ s/ {3}$//;
print Dumper $s;
'
$VAR1 = "foo bar   \r\n";
$VAR1 = "foo bar   \r\n";