pgrep

Search for process names using grep

Display all processes a user is running
pgrep -u user -l
Match a pattern
pgrep -f shell.sh
Display full command

Requires a field argument. 

pgrep -f shell.sh -a
Display PID and binary name
pgrep -l sshd
Display number of processes running matching a name

Useful for cron jobs: 

pgrep -u clients -x rdiff-backup -c