A shell variable is a variable that is available only to the current shell. In contrast, an environment variable is available system wide and can be used by other applications on the system.A shell is the operating system's command interpreter. It processes the commands entered on the command line or read from a shell script file.
Geofencing is a technology that defines a virtual boundary around a real-world geographical area. In doing so, a radius of interest is established that can trigger an action in a geo-enabled phone or other portable electronic device.
Geofencing allows automatic alerts to be generated based on the defined coordinates of a geographic area. A simple example might be an email or text message that is automatically triggered and sent to a user's cell phone when that user's child arrives home from school. In this example, the geofence would be a geographic virtual boundary surrounding the house. When the child's cell phone enters this area, an email is automatically sent to the child's parent by a geofence-enabled app on the phone.
Triggers do not have to happen because of a physical presence. It would be possible to establish a geofence area around a neighborhood and have alerts sent out on garbage collection days based on a schedule entered in a geofence-enabled app by the local government or collection company.
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