Scientia Potentia

With trap, we can safely declare clean-up statements. It is executed on exit from a function, that the exit can either be natural or as the result of an error. The basic syntax is:

trap [action] [condition]

For example, we want to test things on a local database but we want to remove the database if a command exits with a non-zero status (or if an error occurs).

#!/usr/bin/env bash

test_local_db() {
  echo "++ starting test container"
  docker run --name my-test-db -e POSTGRES_PASSWORD=password -d postgres

  on_exit() {
    echo "++ stopping and removing test container"
    docker container stop my-test-db
  }

  trap on_exit EXIT

  # let's say we have an error here:
  echo "++ an error happened!" && exit 1
}

test_local_db

++ starting test container
653c90d1
++ an error happened!
++ stopping and removing test container
my-test-db

More documentation can be seen at man trap.