In general you will want to access the data in some way in the external command. To aid in this process an extra parameter is added to the end of the command specified in the SHELL clause. This parameter is the name of a table. The table will contain the rows affected by the SQL statement that fired the trigger.
The command can read all the data from this table. In general any data written to the table will not be seen by Texis. This is liable to change in the future as enhancements are made to Texis. There is also no current way for the command to stop or rollback the operation.