pipe |

Pass the output of one command as input to the next

The pipe | connects commands; the stdout of the left command becomes the stdin of the right. ps aux | grep nginx passes all processes to grep which filters to nginx lines.

Example

$ ps aux | grep nginx | grep -v grep
root  1234  0.0  0.1 nginx: master process /usr/sbin/nginx

Tip: Type it yourself in the terminal below - reading is not the same as doing.