After first run, the credentials are saved in config file. By default, the config file is ${HOME}/.googledrive.conf.
To change the default config file or use a different one temporarily, see -z / --config custom in Upload Script Custom Flags.
This is the format of a config file:
ACCOUNT_default_CLIENT_ID="client id"
ACCOUNT_default_CLIENT_SECRET="client secret"
ACCOUNT_default_REFRESH_TOKEN="refresh token"
SYNC_DEFAULT_ARGS="default args of gupload command for gsync"
ACCOUNT_default_ROOT_FOLDER_NAME="root folder name"
ACCOUNT_default_ROOT_FOLDER="root folder id"
ACCOUNT_default_ACCESS_TOKEN="access token"
ACCOUNT_default_ACCESS_TOKEN_EXPIRY="access token expiry"
where default is the name of the account.
You can use a config file in multiple machines, the values that are explicitly required are CLIENT_ID, CLIENT_SECRET and REFRESH_TOKEN.
If ROOT_FOLDER is not set, then it is asked if running in an interactive terminal, otherwise root is used.
ROOT_FOLDER_NAME, ACCESS_TOKEN and ACCESS_TOKEN_EXPIRY are automatically generated using REFRESH_TOKEN.
SYNC_DEFAULT_ARGS is optional.
A pre-generated config file can be also used where interactive terminal access is not possible, like Continuous Integration, docker, jenkins, etc
Just have to print values to "${HOME}/.googledrive.conf", e.g:
printf "%s\n" '
ACCOUNT_default_CLIENT_ID="client id"
ACCOUNT_default_CLIENT_SECRET="client secret"
ACCOUNT_default_REFRESH_TOKEN="refresh token"
' >| "${HOME}/.googledrive.conf"
Note: If you have an old config, then nothing extra is needed, just need to run the script once and the default config will be automatically converted to the new format.