/usr/bin/unexpand

Usage: /usr/bin/unexpand [OPTION]... [FILE]...
Convert blanks in each FILE to tabs, writing to standard output.

With no FILE, or when FILE is -, read standard input.

Mandatory arguments to long options are mandatory for short options too.
  -a, --all
         convert all blanks, instead of just initial blanks
      --first-only
         convert only leading sequences of blanks (overrides -a)
  -t, --tabs=N
         have tabs N characters apart instead of 8 (enables -a)
  -t, --tabs=LIST
         use comma separated list of tab positions.
         The last specified position can be prefixed with '/'
         to specify a tab size to use after the last
         explicitly specified tab stop.  Also a prefix of '+'
         can be used to align remaining tab stops relative to
         the last specified tab stop instead of the first column
      --help
         display this help and exit
      --version
         output version information and exit

Report bugs to: <bug-coreutils@gnu.org>.
GNU coreutils home page: <https://www.gnu.org/software/coreutils/>
General help using GNU software: <https://www.gnu.org/gethelp/>
Full documentation <https://www.gnu.org/software/coreutils/unexpand>
or available locally via: info '(coreutils) unexpand invocation'