Command:   unexpand - convert spaces to tabs
Syntax:    unexpand [-a]
Flags:     -a  All spaces are unexpanded
Example:   unexpand oldfile >newfile # Convert leading spaces to tabs

     Unexpand replaces spaces in the named files with tabs.  If no files
are  listed, stdin is given.  The -a flag is used to force all sequences
of spaces to be expanded, instead of just leading spaces (the default).