Command subsystem introduction
The command syntax differs from the conventions used in the underlying operating systems.
A command consists of a command name followed by a list of command parameters.
General syntax:
COMMAND reqpos ... optpos ... / KEYWORD(opt) ...
Three different types of command parameters are possible.
- Required positional parameters.
These parameters are always required by the system and cannot be
defaulted. They are entered as values (numbers or character
strings) immediately following the command name and are
identified by the order in which they appear.
- Optional positional parameters.
They are also identified by the order in which they appear but
may be omitted causing default values to take effect. Individual
parameters may be defaulted by the use of adjacent commas. The
list as a whole may be truncated from the end (right to left).
- Optional parameters.
Optional parameters are identified by a name (keyword) which may
be followed by a value (number(s) or character string) enclosed
in parantheses. Separated by the special character '/' from the
list of positional parameters, they may be entered in any order.
If omitted, default values take effect.
Optional parameters without an argument act as a switch having
the two possible values '0' and '1', equivalent to "false" and "true",
respectively.
Each optional parameter is provided with a default value. Two
kinds of default values are possible:
- Static defaults.
Their values are unchanged and take effect each time the
corresponding parameters are not explicitely specified.
- Replaceable defaults.
They act like static defaults, but their values are overwritten
by the corresponding parameter values used last.
Items in a positional parameter list must be separated by blanks or commas.
Protecting delimiters
If a positional parameter value includes delimiters, i.e. blanks, commas or
slashes (e.g. in filenames), it must be enclosed in single or double quotes.
Example:
EXEC "mydir/myfile"
Abbreviations
Most command and parameter names may be abbreviated as long as
the remainder is unique.
Example:
DISP A LIST / WINDOW(100,260)
is equivalent to
D A LIST / W(100,260)
Omitting optional positional parameters
A list of optional positional parameters can only be truncated
from the end (right to left). However, an individual item may be
omitted if a comma is typed instead.
Example:
Assume the command EXAMPLE is defined with three positional
parameters. Then with:
EXAMPLE ,B C
EXAMPLE A,,C
EXAMPLE ,,C
EXAMPLE A
the 1st parameter,
the 2nd parameter,
the 1st and 2nd parameters,
and the 2nd and 3rd parameters, respectively.
are defaulted.
Last updated: M.Kraemer@gsi.de, 31-May-1999