Sometimes working from command line might require to know which shell you are currently using. To find out the current working shell, below steps will be helpful:
Try below command first:
ps -p $$
PID TTY TIME CMD 2248 pts/8 00:00:00 bash
Another command which also works on MAC OS and other Linux distributions:
The above commands work on RHEL, CentOS, Ubuntu, Fedora, Mac OS and Debian.