my version="1.4";
my $rcs = Rcs->new;
$rcs->co('-r $version');
or
$rcs->co('-r$version');

##</code><code>##

co: /auto/data/Test/TestCase/public/TC11544.xml,v: improper revision number:  $version

##</code><code>##

$rcs->co('-r1.4');

##</code><code>##

my $verfile=`co -r$version`;
$rcs->co("-r" => "$version");
my $verfile=`co -r $version`;

##</code><code>##

co: /auto/data/Test/TestCase/public/TC11544.xml,v: improper revision number:  $version

##</code><code>##

co: RCS/1.4,v: No such file or directory