kill

kill sends a signal to one or more processes, usually to ask to terminate or force them to stop

kill app / process by name

works also for things like Codex.app on macOS, since -f matches the whole command:

list matching processes:

pgrep -af 'Codex.app'
pgrep -fl 'Codex.app'

kill matching processes:

pkill -f 'Codex.app'
pkill -f '/Applications/Codex\.app/' # might be safer if it matches other apps, too

terminate exact process

this matches the exact process name:

pgrep -ax codex
pgrep -xl codex

this ends the process:

pkill -x codex