IRAF help page for package language, program scan

• pN
• param

scan -- read parameters from standard input fscan -- read parameters from file, or another parameter nscan -- get number of parameters scanned

USAGE

scan  (p1, p2, p3 ... pn)
fscan (param, p1, p2, p3, ... pn)
n = nscan()

PARAMETERS

pN

param

Scan and fscan permit the user to read in values from the standard input, a file, or a parameter and assign them to the listed parameters. Fscan may also be used to read a string already in core. It is useful to consider these functions as performing two disjoint actions: acquiring a string, where scan and fscan differ; and parsing the string, where they are identical.

Scan acquires its string by reading exactly one line from the standard input. The action of fscan depends on param. If param is a string, or a struct, then the string is simply the value of param. If, however, param is a list-directed struct, a call to fscan will get the next line from the file pointed to by param. The file can be rewound by assigning a file name to param. If either scan or fscan reach an EOF, they return with the value EOF and do not change any parameters.

Once the string has been acquired it is parsed into segments delimited by spaces or tabs. Scan and fscan do not recognize quoted strings, nor do they view ',' as a delimiter. Each token is then assigned in turn to p1 through pn. If there are too many tokens they are discarded, if there are too few, the corresponding parameters are not affected by the call. Any conversion error terminates the scan, but parameters already scanned retain their new values. An assignment to a struct terminates the scan because the entire unscanned portion of the string is assigned to the struct. Thus any struct should be the last parameter in a scan or fscan call.

Scan and fscan are intrinsic functions returning either EOF if end of file on the input list is sensed, or the number of parameters successfully scanned. The function nscan also returns the number of parameters successfully scanned in the last call to scan or fscan.

1. Print a list of radii, given a list of coordinates.

	list = coords
	while (fscan (list, x, y) != EOF)
	    print (sqrt (x**2 + y**2))

BUGS The syntax of scan and fscan is peculiar, in that they are the only functions where parameters are effectively passed by reference rather than by value. Thus p1, ... pn must be parameters whereas in similar contexts an arbitrary expression can be used wherever a parameter can.

string,