VISTA Command Syntax

VISTA works by calling various subroutines from a set of libraries. You tell VISTA what to do by entering commands.

Commands come in several types. The simplest commands, such as 'QUIT' (which halts VISTA) work on no data and only operate in one way. Commands that manipulate images or spectra have an 'object' that the command operates on. You should always specify the object immediately after the command. An example of this is 'ZAP 1' which performs the ZAP operation (q.v.) on image number 1. More complicated commands have 'keywords' that control their operation. Keywords allow you to tailor the operation of the command to suit your needs. An example of a command with keywords is

Keywords can appear in any order on the command line. The allowed keywords for any command can be found by entering the command name followed by a '?'; e.g. BOX ? will list all the allowed keywords for the BOX command.

All of the objects and keywords for a command must appear on the same line as the command. The command name ALWAYS comes first. Several commands may be placed on a single line, separated by semicolons. An example of this is:

Command lines are split by the VISTA parser into individual words. The parsing uses blank spaces to separate words, with the consequence that you cannot put blank spaces within a word/keyword. For example, the simple arithmetic statement:

will not work if there are any embedded blank spaces. Strings can have embedded blank spaces if the entire string in enclosed in single quotation (') marks.

A command can be extended over more than one line by using the character at the end of the line. Type HELP EXTEND if you are at a terminal for more information about this feature. This information is also in section 2 of this manual.

Any character can appear on the command line, but characters after the first occurrence of ! in a command are ignored. The ! is the VISTA 'comment character', providing a way to label individual commands. Here is an example of a command with a comment:
$\begin{hanging} \item{SUBTRACT 1 CONST=40.3 ! Subtract 40.3 from image 1.} \end{hanging}$
Commenting commands is very handy in procedures.

Buffer numbers always take the form of integer constants. These are used to denote buffers that store the images and spectra. They must not have a decimal point: for example, '1' is an integer constant, while '1.' is not. A very important exception to this rule is the '$' construction which allows you to use variables to denote objects. See OBJECT (type HELP OBJECT if you are on a terminal) for information.

Keywords come in several types:

REAL CONSTANTS: These are numbers containing a decimal point (e.g., '3.14'), and are used as input to programs that require a numeric value as a parameter. An example of a command with a real constant in it is
```
	   TV 2 1024.0
```
WORDS: These are single or multiple words without an '=' sign in them. Most words turn on or off options in the programs. An example is:
```
         CONTOUR 1 DASH NOERASE
```
IMPORTANT: Sometimes you will want to consider several words as a unit. Multiple words used in this way must be enclosed in single quotes. An example is the CHANGE command, which changes the name of an image. If you wanted the new name to be a single word, you could say:
```
         CHANGE 3 NGC5128
```
but if the new name has several words in it, you would need quotes, so:
```
         CHANGE 3 'NGC5128 - through clouds '
```
KEYWORD VALUES. These are combinations of keywords and arithmetic constants, and are used to pass values to VISTA subroutines, where needed. Keyword values have the form 'WORD=value': i.e., a keyword immediately followed by an equal sign, immediately followed by a constant. The constant can be either explicit or symbolic, for example, these two command lines:
```
         SHIFT 1 DR=2.3
         SHIFT 1 DR=INCR
```
do the same thing, provided INCR has the value 2.3. You can also use arithmetic expressions following the '=' sign, as in
```
         SHIFT 1 DR=INCR+3.2
```

VISTA takes the command line, and splits it up into several lists: a list of integers, a list of floating-point numbers, and a list of character strings. The programs in VISTA examine these lists to decide what to do.

Most commands check the input line to make sure that every word you give is something the command knows about. If you type an unknown command, you will receive an error message, and the command that you are trying to execute will not run.

More information about command syntax can be found in section 2 of this manual.