Modification times in records?

I'm looking for a generalized way to set a field to 'now'
whenever a record is updated.

First, I started creating a plpgsql function for each table that
I needed this for, and then using a trigger.

Later, I realized that the functions were all identical, so I
created one function, which lukily was always updating a field
with the same name.

I'm looking for a way to specify a field name when I create the
trigger, so I can have one function and assign it to any table
with any timestamp field and have it update automagically.
I can't seem to get a parameter into the function. Any ideas?

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Adam Haberlach |A cat spends her life conflicted between a
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