MIDAS commands fall into two categories:
the basic commands and all other application
commands. The basic commands are executed inside the MIDAS monitor, which
is the program you are interacting with.
All other commands are implemented by executing a MIDAS procedure which
runs one or more programs in a subprocess (child process).
During the time a command is being processed in the subprocess,
the MIDAS
monitor is suspended until the corresponding program terminates in the
subprocess. Only then control is returned to the user. To stop a
command prematurely, type 
.
Since process creation is much more expensive in VMS than in Unix
these subprocesses are handled differently in VMS and Unix:
In VMS, the subprocess, named FORGRxy (with xy the MIDAS unit specified at
start--up), is created at MIDAS initialisation
time and kept alive until you exit from MIDAS via the command BYE.
In Unix, the
child process is created each time the MIDAS command executes an
application program.
Upon termination of that program the child process dies.
This also applies to commands of the host system -- they are executed
in a subshell.
Therefore, issuing `$ cd /elsewhere' inside MIDAS does not change
your current directory permanently...
See also section
about the change-directory problem.
Some internal files are created when starting a MIDAS session in the directory
specified via MID_WORK:. The most important ones are the
keyword file and the logfile.
The keyword file is named FORGRxy.KEY ( xy the MIDAS unit)
and holds the keyword data
base accessible by all programs running in the MIDAS environment.
The logfile is named FORGRxy.LOG and receives a log of all user
input and all MIDAS output
on the terminal (except HELP text, as explained before, and output
from the host system).
The logfile serves also as a ``fall back'' utility in case of system crash
or other breakdown. In such a case the command PLAYBACK/LOG `logfile'
may be used to regenerate the complete MIDAS session.
Note order to use the playback facility, you have to rename the original logfile before restarting MIDAS via INMIDAS or inmidas. Remember that INMIDAS deletes old MIDAS logfiles unless you run in parallel mode .