.help unlearn Feb86 language
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NAME
unlearn -- restore initial defaults for parameters
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USAGE
unlearn name [name ...]
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PARAMETERS
.ls name
An IRAF task or package name.
.le
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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 \fIunlearn\fR 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.
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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 \fIdataio\fR package.

	cl> unlearn dataio

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

.nf
	cl> chdir uparm
	cl> delete *.par
.fi
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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.
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SEE ALSO
cache, update, lparam, eparam
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