GIMP Remote is another support program for GIMP. It allows you to open an image from the command line in an already running GIMP. The format is:
[gimp-remote options ... files ...]
GIMP Remote Options
[-h] [--help]
Displays a list of available options, and gives a terse description of each one.
[-v] [--version]
Prints the version number of the installed GIMP.
[-n] [--new]
Opens a new instance of GIMP if one is not already available.