ps -C nginx --no-header |wc -l

[root@ok ok]# ps --help|grep C
-A all processes                      -C by command name
-V,V  show version      L  list format codes  f  ASCII art forest
-w,w  wide output       n  numeric WCHAN,UID  -H process hierarchy
#-C 命令的名子

[root@xxxx tools]# ps -C nginx --no-header
  ?        :: nginx
 ?        :: nginx
 ?        :: nginx
 ?        :: nginx
 ?        :: nginx
[root@xxxx tools]# ps -C nginx
  PID TTY          TIME CMD #--no-header　省去title
  ?        :: nginx
 ?        :: nginx
 ?        :: nginx
 ?        :: nginx
 ?        :: nginx