CESM recommends using the xmlchange tool to modify env variables. xmlchange supports error checking as part of the implementation. Also, using xmlchange will decrease the chance that typographical errors will creep into the xml files. Conversion of the xml files to environment variables can fail silently with certain xml format errors. To use xmlchange, do, for instance,
> cd $CASEROOT > ./xmlchange -id STOP_OPTION -val nmonths > ./xmlchange -id STOP_N -val 6
which will change the variables STOP_OPTION and STOP_N in the file env_run.xml to the specified values. The xml files can be edited manually, but users should take care not to introduce any formatting errors that could lead to incomplete env settings. See also .