until

Simple shell loop that repeats until it receives zero as return value. More information: https://www.gnu.org/software/bash/manual/bash.html#index-until.

• Execute a command until it succeeds:

until command; do :; done

• Wait for a systemd service to be active:

until systemctl is-active --quiet nginx; do echo "Waiting…"; sleep 1; done; echo "Launched!"