balenaOS shell script to get a full container name given the service name

get_container_name.sh

#!/bin/bash

# Get a full container name given its short service name.
# The full container name can then be used as argument for
# the `balena-engine exec` command.
#
# Usage instructions:
#
# * Save this file somewhere, e.g.:
#   $ vi /tmp/get_container_name.sh
#
# * Give it executable permissions (one off) with:
#   $ chmod +x /tmp/get_container_name.sh
#
# * Run it with the service name as argument, and it will print
#   the full container name as output:
#   $ /tmp/get_container_name.sh main
#   main_4578820_2075969_8746957653480dc984ab2dc8fd6587c7

function get_container_name {
        local service="$1"
        local len="${#service}"
        local -a names
        readarray -t names <<< "$(balena-engine ps --format '{{.Names}}')"
        local result=''
        local name
        for name in "${names[@]}"; do
                if [ "${name:0:len+1}" = "${service}_" ]; then
                        result="${name}"
                        break
                fi
        done
        echo "${result}"
}

get_container_name "$@"