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

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