Hmmm. It seems that the "Extraneous `c' flag ignored" error message has
vanished in 3.11pre4 (or maybe sooner) when you add a `c' to a filter recipe
or to a variable capture recipe.
If you put a `c' on a filtering recipe, there is no error, and the filter
still changes the original copy. The only change in behavior is that if
you have a logfile set and LOGABSTRACT=all, you get a logabstract for the
filtering action. The entry in the logabstract for Folder:, however, is
blank; it doesn't contain the action line, as it would for a pipe recipe.
Similarly, if you put a `c' on a variable capture recipe there is no error.
If you have a logfile set and LOGABSTRACT=all, you get a logabstract for the
variable capture recipe, and the Folder: line of the logabstract contains
the value assigned to the variable (again, not the command but the output).
In one case where I wanted the command logged, I had to code like this:
:0 # no `c' since this in the long run wasn't the recipe I wanted logged
* conditions
VARIABLE=| command
:0acbi # `b', not `h', because usually this runs on mail with short bodies
LASTFOLDER=|echo ' 'same_command
For either filtering recipe or variable capture recipes, without `c', there
is no logabstract, but everything else works the same.