ICL command parameters

Parameter value specifications in an ICL command can take three forms:

• An expression enclosed in parentheses. E.g.

      (2)        (X)         (Y*SIN(THETA))
  

• A string enclosed in quotes. E.g.

      `String'               "Filtered and calibrated"
  

• Any sequence of characters not including a space, quote, comma or left parenthesis. E.g.

      NGC1635    X           PI*2
  

The first form is used to pass the value of an ICL expression to a command, or to give a command a variable in which to return a value. The other two forms both pass a string.

We can illustrate the three forms by using the PRINT command which prints its parameter values on the terminal:

    ICL> X=1.234
    ICL> PRINT (X)
    1.234000
    ICL> PRINT 'HELLO'
    HELLO
    ICL> PRINT HELLO
    HELLO

In many cases you do not need to use the quoted form of a string because the simpler form will work. You need the quoted form for those cases in which you need to delimit a single string containing a left parenthesis or spaces. Consider the following example which contains a PRINT command which has several parameters:

    ICL> X=2
    ICL> PRINT The Square Root of (X) is (SQRT(X))
    The Square Root of          2 is 1.414214

Since spaces are parameter separators, `The', `Square', `Root', and `of' are all received by PRINT as separate parameters. However, PRINT simply concatenates all its parameters with a space between each pair. Thus, the output written by PRINT is the string, just as you typed it. Many other ICL commands which accept strings work in this way. This means that strings with single spaces may not need quotes when used as command parameters. However, in general this is not true of commands which run ADAM programs when strings are specified on the command line (see below).

The rules for specifying ICL command parameters can be summarized as follows:

• To pass the value of an expression or the name of a variable, enclose it in parentheses.
• Anything not in parentheses is passed as a string, or as a sequence of strings if it contains spaces or commas.
• Any string which does not fit these restrictions can be passed by placing it in quotes. Quotes may be included in a string by typing two consecutive quotes.