Description
Assumes that the value of the string is a valid file name, and redirects ij processing to read from that file until it ends or an Exit command is executed. If the end of the file is reached without ij exiting, reading will continue from the previous input source once
the end of the file is reached. Files can contain Run commands.
ij prints out the statements in the file as it executes them.
Any changes made to the ij environment by the file are visible
in the environment when processing resumes.