unexpand
[options] [files]Convert spaces back into an appropriate number of tab characters. unexpand reads the named files, or standard input if no files are provided. See also expand.
-a
Replace spaces with tabs everywhere possible, not just leading spaces and tabs.
-t
tablistInterpret tabs according to tablist, a space- or comma-separated list of numbers in ascending order that describe the "tabstops" for the input data.