replaceval
Usage:
replaceval <old-val> <new-val> <colid-list>
For each column specified in <colid-list>
any instance of <old-val> is replaced by
<new-val>.
The value string 'null' can be used for either
<old-value> or <new-value>
to indicate a blank value
(but see also the badval
filter).
Syntax for the <colid-list> argument is described in Section 6.3.