ps | grep $$ | awk '{print $4}'

$ echo $SHELL

$ echo $0

env | grep SHELL

cat /etc/passwd | grep muye

$ ps -ef | grep $$ | grep -v grep | grep -v ps

<a href="mailto:muye@bupt:~$">muye@bupt:~$</a> ps -ef | grep $$
muye 4750 4745 0 15:47 pts/1 00:00:00 bash
muye 5331 4750 0 16:51 pts/1 00:00:00 ps -ef
muye 5332 4750 0 16:51 pts/1 00:00:00 grep --color=auto 4750