$ echo 0 > rdwr
$ echo 0 > tie
$ cat rdwr
0
$ cat tie
0
$ perl prog.pl rdwr tie
new value for rdwr: 1
new value for tie: 1
$ cat rdwr
0
1
$ cat tie
0
1
... and some executions later..
$ cat rdwr
0
1
2
3
4
5
$ cat tie
0
1
2
3
4
5