Care has been taken that MIDAS and the Host Operating System (DCL for VMS and
Bourne or C-shell for Unix) co--exist
smoothly and complement each other.
Migration from one environment to the other is simple:
If you are in the MIDAS environment, type BYE
to switch back to the Host System.
If you have returned to the host environment from a MIDAS session,
(indicated by the $--prompt in VMS, and by $ or % in Unix), type
GOMIDAS (in VMS) or gomidas (in Unix)
to revive MIDAS.
The status of the keywords and the
command buffer of the stopped MIDAS session are
preserved - if you want to start afresh, use INMIDAS (VMS) or
inmidas (Unix) again.
You may also use host commands directly inside MIDAS
by preceding them with ` $'. For instance,
Midas 027> $DIR (in VMS) or
Midas 027> $ls (in Unix)
will display the contents of the current directory.
Please, note, that currently this mode of operation will only invoke Bourne
shell commands in Unix, not C-shell or Kornshell commands.
To execute C-shell (or any other Shell) commands you have to insert them
in a Bourne shell script which has as the first line: 
! /bin/csh,
or: 
! /bin/ksh, etc.
Note If you work on a VMS system, beware of DCL command procedures:
DCL modifies command I/O streams when executing a procedure. This causes problems for the interprocess communication inside MIDAS. When executing a DCL procedure via $ @ `procedure' the correct settings will be maintained inside MIDAS.
However assigning a symbol MIMI to the command above and then executing the DCL procedure by just typing $ MIMI will lead to disaster from which only a BYE and subsequent GOMIDAS will get you going again.
Since images, tables, etc. are standard disk files, all host commands related to
file operations can be employed. However, if a MIDAS catalog is used, care has
to be taken that the information in the catalog is not invalidated, when e.g.
renaming or deleting data files outside MIDAS (i.e. using commands of the host
file system directly).
The output from MIDAS commands can be redirected to ASCII files enabling
easy combination of MIDAS and host commands. E.g.
Midas 0123> READ/DESCR myimage * >dsc.dat
will send all the output from the READ/DESCR command to the ASCII
file dsc.dat (created in your current work directory)
which can then be used by any host command. For example,
Midas 124> $EDIT dsc.dat (in VMS) or
Midas 124> $vi dsc.dat (in Unix)
On a Unix system you can pipe
the MIDAS output directly to a Unix command, e.g.
Midas 0123> READ/DESCR myimage * >| grep NGC425