usage:

java <Java-options> -jar josm.jar <options> [file]

options:

--help|-h                                 Show this help
--geometry=widthxheight(+|-)x(+|-)y       Standard unix geometry argument
[--download=]minlat,minlon,maxlat,maxlon  Download the bounding box
[--download=]<URL>                        Download the location at the URL (with lat=x&lon=y&zoom=z)
[--download=]<filename>                   Open a file (any file type that can be opened with File/Open)
--downloadgps=minlat,minlon,maxlat,maxlon Download the bounding box as raw GPS
--downloadgps=<URL>                       Download the location at the URL (with lat=x&lon=y&zoom=z) as raw GPS
--selection=<searchstring>                Select with the given search

--[no-]maximize                           Launch in maximized mode
--reset-preferences                       Reset the preferences to default
--load-preferences=<url-to-xml>           Changes preferences according to the XML file
--set=<key>=<value>                       Set preference key to value
--language=<language>                     Set the language
--version                                 Displays the JOSM version and exits
--debug                                   Print debugging messages to console
--skip-plugins                            Skip loading plugins
--offline=<osm_api|josm_website|all>      Disable access to the given resource(s), separated by comma

options provided as Java system properties

-Djosm.pref=/PATH/TO/JOSM/PREF            Set the preferences directory
-Djosm.userdata=/PATH/TO/JOSM/USERDATA    Set the user data directory
-Djosm.cache=/PATH/TO/JOSM/CACHE          Set the cache directory
-Djosm.home=/PATH/TO/JOSM/HOMEDIR         Relocate all 3 directories to homedir.
-Djosm.home=/path/to/JOSM/folder/         Change the folder for all user settings. Cache directory will be in homedir/cache

Note: -Djosm.home has lower precedence, i.e. the specific setting overrides the general one

For some tasks, JOSM needs a lot of memory. It can be necessary to add the following Java option to specify the maximum size of allocated memory in megabytes. On the other hand, on slow systems or those with less memory, you can make JOSM more stable by restricting its memory use:

-Xmx...m                                  Set maximum Java heap size in megabytes

examples

java -jar josm.jar track1.gpx track2.gpx london.osm
java -jar josm.jar https://www.openstreetmap.org/#map=13/43.2/11.1
java -jar josm.jar london.osm --selection=http://www.ostertag.name/osm/OSM_errors_node-duplicate.xml
java -jar josm.jar 43.2,11.1,43.4,11.4
java -jar josm.jar --set=expert=true
java -Djosm.pref=$XDG_CONFIG_HOME -Djosm.userdata=$XDG_DATA_HOME -Djosm.cache=$XDG_CACHE_HOME -jar josm.jar
java -Djosm.home=/home/user/.josm_dev -jar josm.jar
java -Xmx1024m -jar josm.jar

Parameters --download, --downloadgps and --selection are processed in this order. Make sure you load some data if you use --selection.