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Parameters

IRAF supports two kinds of parameters, auto parameters and hidden parameters, which are treated differently.

• auto parameters are updated every time a task is run. The user will be prompted for them unless they are explicitly given on the command line.

• hidden parameters are those which can be reasonably defaulted, i.e. are often the same from one run of a task to the next. They need to be explicitly changed for choices different than the default. They are denoted in parameter listings by parentheses.

Parameters for each task are contained in `parameter files' in the uparm sub-directory in `myiraf'. A copy of each file with the latest parameter setup is saved after use. A list of parameters for a specific task can be obtained by typing:

  cl > lparam taskname

For example, there are several ways of typing commands to examine the header of an IRAF image e.g. dev$pix [a test image within the IRAF system]:

  cl > images                                               # load package

  im > imhead                    # Will prompt the user for the input file
  im > imhead dev$pix                # will display the dev$pix.imh header
  im > imhead dev$pix longheader=yes     # A more verbose display obtained
                                            # by changing the value of the
                                             # hidden parameter longheader
  im > imhead dev$pix.imh long+     # Alternative way to set the parameter
                                                              # longheader

Hidden parameters can be permanently changed in two ways:

  im > imhead.longheader=yes   # explicitly setting <task.param>=<value>
  im > eparam imhead     # Edit the parameter file to update one or more
                                           # parameters at the same time
                                                      # see next section