Q: What is smenu?

A: smenu is a selection tool which acts as a filter that takes words
   from the standard input or a file and presents them on the screen in
   various ways in a scrolling window.

   A cursor that you can easily move allows you to select one or more
   of them.

   The selected words are printed on the standard output.
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Q: Why smenu tells me: "The length of a word has reached the limit of
   512 characters." but there is no such word in my entry?

A: There is a good chance you have an unbalanced quote, single or double,
   somewhere. smenu uses quotation marks to be able to have spaces in
   'words', and these quotation marks that do not serve as delimiters
   must be protected.

   You can use something like: sed -e "s/'/\\\'/g" -e 's/"/\\"/g' to
   pre-process the input in such a case.
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Q: Why does smenu -C... no longer work?

A: smenu uses a new system of options based on the notion of contexts. The
   -C parameter is only valid in the "Columns" context as indicated in the
   error message.

   The string '[-c|-col|-col_mode|-column>Columns]' which is printed
   in the error message tells that to switch to "Columns" mode
   you have to use the -c parameter or its alternatives.
   So in this case the correct command line is: smenu -c -C...