bash escape

When running the following script I get:

Fatal Error: The file specification '/**
cannot match any files in the base directory /full/path
Useful file specifications begin with the base directory or some pattern (such as '**') which matches the base directory.

The command work as expected when executed from shell

#/bin/bash
export FTP_PASSWORD="password"
USERNAME="backup"
DOMAIN="domain.com"
CONTAINER="folder"
ROOT_PATH="/full/path"
export PASSPHRASE=passphrase
#options="--exclude '**.tar.gz'"

duplicity $OPTIONS $ROOT_PATH gdocs://$USERNAME@$DOMAIN/$CONTAINER
unset PASSPHRASE
unset FTP_PASSWORD