More boring use of symlinks 

$ ls -l
-rwxr-xr-x grant grant 14891 2009-03-09 nethack.pl
lrwxrwxrwx grant grant    10 2009-03-09 client -> nethack.pl
lrwxrwxrwx grant grant    10 2009-03-09 server -> nethack.pl

• In the script ...

if(basename($0) eq 'server') {
    run_server();
}
else {
    run_client();
}