How do I replace whitespaces with tabs in linux in a given text file?
UNEXPAND(1) User Commands UNEXPAND(1)
NAME
unexpand - convert spaces to tabs
SYNOPSIS
unexpand [OPTION]... [FILE]...
DESCRIPTION
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 (enables -a)
--help display this help and exit
--version
output version information and exit
. . .
STANDARDS
The expand and unexpand utilities conform to IEEE Std 1003.1-2001
(``POSIX.1'').