Number of open connections can be found out by using below query:
mysql -e 'SHOW STATUS WHERE variable_name LIKE "Threads_%" OR variable_name = "Connections"'
+-------------------+-------+
| Variable_name | Value |
+-------------------+-------+
| Connections | 862 |
| Threads_cached | 0 |
| Threads_connected | 10 |
| Threads_created | 26 |
| Threads_running | 1 |
+-------------------+-------+