Open the file given by filename and read it line by line, executing each line. This allows you to store commands in a script file and then execute this script. Typically the KILLALL command will be used to clear memory before reading the file.
The second form of this command reads data from the nth file (opened with the FILE command). If n is 1-5, then the file is a text file and rec is the line number to read. If rec is zero or omitted, the next sequential line is read. If n is 6-10, then the file is a structured file, and the record indicated by rec is read. If rec is zero or omitted, the next record is read.
When reading from a file, argument references such as %1 are normally expanded using the arguments given in the #READ command. If the third parameter is _noexpand, then the line from the file is executed without replacing arguments.