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<H1><A NAME="SECTION00650000000000000000"> </A>
<A NAME="execution-of-commands"> </A>
<BR>
Execution of Commands
</H1>
<P>
MIDAS commands fall into two categories:
the <I>basic</I> commands and all other <I>application</I>
commands. The <I>basic</I> 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<A NAME="1783"> </A> 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
<!-- MATH: $\fbox{\tt Ctrl/C}$ -->
<IMG
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<BR>
Since process creation is much more expensive in VMS than in Unix
these subprocesses are handled differently in VMS and Unix: <BR>
In VMS, the subprocess, named FORGRxy (with <TT>xy</TT> the MIDAS unit specified at
start-up), is created at MIDAS initialisation
time and kept alive until you exit from MIDAS via the command <TT>BYE</TT>. <BR>
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.
<BR>
Therefore, issuing <TT>`$ cd /elsewhere'</TT> inside MIDAS does not change
your current directory permanently... You should use the MIDAS command
<TT>CHANGE/DIRECTORY</TT> instead. See section
<A HREF="node23.html#starting-the-midas-monitor">3.1</A> about the <I>change-directory</I> problem. <BR>
<BR>
Some internal files are created when starting a MIDAS session in the directory
specified via <TT>MID_WORK:</TT>. The most important ones are the
<I>keyword file</I> and the <I>logfile</I>.
<BR>
The <I>keyword file</I><A NAME="1794"> </A> is named <TT>FORGRxy.KEY</TT> (<TT>xy</TT> the MIDAS unit)
and holds the keyword data
base accessible by all programs running in the MIDAS environment. <BR>
The <I>logfile</I><A NAME="1798"> </A> is named <TT>FORGRxy.LOG</TT> 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 <I>logfile</I> serves also as a ``fall back'' utility in case of system crash
or other breakdown. In such a case the command <TT>PLAYBACK/LOG `logfile'</TT>
may be used to regenerate the complete MIDAS session.
<P>
<BLOCKQUOTE>
<DIV ALIGN="CENTER">
<B>Note</DIV>
<I>In order to use the playback facility, you have to rename the
original logfile
before restarting MIDAS via <TT>INMIDAS</TT> or <TT>inmidas</TT>.
Remember that INMIDAS deletes old MIDAS logfiles unless you run in
<TT>parallel</TT> mode<A NAME="1806"> </A>.</I></B></BLOCKQUOTE>
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<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-09</I>
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