you can also check that it matches the characters you're looking for followed by one or more non-space, such as:

my $mystring = "Rescue21_binaries_V5.0.29.0_patch_R5.0.24.1_DiffList.t
+xt";

if($mystring =~ m/Rescue21[^\s]+?patch[^\s]+?DiffList.txt/ ) {
    print "Matched" . "\n";
}
[download]

hope that helps