unlearn: Restore the default parameters for a task or package

Package: language

Usage

unlearn name [name ...]

Parameters

name: An IRAF task or package name.

Description

Normally when a task terminates the values of the query mode task parameters used are stored in the parameter file on disk, appearing as the new defaults the next time the task is run. The unlearn command instructs the CL to forget any task parameters it might have learned and to use the initial default values the next time the task is run. If a tasks parameters have been cached, then they are removed from the parameter cache.

If a package name is specified all the tasks in the package are unlearned.

Examples

1. Unlearn the parameters for the delete and plot.graph tasks.

cl> unlearn delete plot.graph

2. Unlearn the parameters for all tasks in the dataio package.

cl> unlearn dataio

3. To unlearn the parameters for all tasks in the system, log out of the CL and run mkiraf, or enter the following:

cl> chdir uparm
cl> delete *.par

Bugs

It is possible for the parameter set for a task to become corrupted, e.g., if the CL is interrupted while it is updating the parameter file on disk, causing a truncated file to be written. If this should occur one will get error messages complaining about illegal arguments or parameters not found when the task is run. The fix is to "unlearn" the parameters for the task.

When the CL fetches the parameters for a task, it checks to see if the system defaults have been updated more recently than the user's copy of the parameter set, and uses the system copy if it is more recent, after printing a message to warn the user. This is done by comparing the file dates for the system and user parameter sets. On VMS, it is easy for the modify date of the system copy of the parameter set to become updated even though the file data has not been modified, causing an annoying warning message to be printed when the task is later run. Should this occur, the best solution is to unlearn all affected parameter sets.