The ESO-MIDAS system provides general tools for image processing and data reduction with emphasis on astronomical applications including imaging and special reduction packages for ESO instrumentation at La Silla and the VLT at Paranal. In addition it contains applications packages for stellar and surface photometry, image sharpening and decomposition, statistics and various others.

The MIDAS command language, MCL, provides the tools to construct complex command procedures from existing commands. Since all application programs get their parameters via a set of standard interfaces, it is very simple to string commands together, each using results from the previous command. In fact, except for the system commands, all MIDAS commands are MCL procedures themselves.

MCL is an interpreted language which means that the definition of local variables may be done anywhere in a procedure and no compilation and linking steps are required before executing a MCL procedure. To identify syntax and other obvious errors in long and complicated procedures the MIDAS Command Language Debugger is provided. It enables debugging of procedures as well as application code (F77 and C).

MIDAS is a command driven system in which the user enters commands followed by parameters. This implies that the user must know a few commands and their structure in order to make effective use of the system. Since most users cannot keep all the commands and their parameters at their finger tips, an extensive on-line help facility has been created which can be used within the Midas terminal window as well as via a graphical user interface.

A MIDAS command has the following structure:

COMMAND/QUALIFIER par1 par2 … par8

where par1 is the first parameter and so on. The important points are:

• Command and qualifier are separated by a / (slash).
  
• The command/qualifier and the parameters are separated by a space.
  
• Most commands have qualifiers.
  
• A parameter may contain several sub-parameters which are separated by commas.
  
• In most cases if the parameters are not specified, the system makes sensible defaults, but the user should not always trust these default values to be those he might have chosen.
  
• Keep these rules in mind, otherwise you will confuse the command.
  

MIDAS commands divide themselves into three categories:

• MIDAS basic (system) commands
  
• MIDAS application commands
  
• procedure control commands
  

All MIDAS commands are listed in alphabetical order and explained in detail in help graphical user interface of MIDAS or can be found on the home page of ESO Midas. The application commands are developed for special purposes such as CCD or CASPEC reductions. They are described and listed in the various sections related to particular applications. For reductions of data you should refer to Volume B of the Midas manual.

A guide to useful info about Midas which is difficult to dig out from the official documentation.

The detailed description for all commands available can be accessed via the Midas GUI XHelp (from the shell with helpmidas or from Midas with create/gui help).