Options for unexpand command

• -a, – -all option : This option is used to convert all blanks, instead of just initial blanks (which is by default). 

/* This converts all the blanks 
   also into tabs */
$unexpand -a kt.txt>dv.txt

• – -first-only option : This is used to convert only leading sequences of blanks (overrides -a option). 

/* This converts only the leading
   sequences of blanks */
$unexpand --first-only kt.txt>dv.txt

• -t, – -tabs=N option : This set tabs N characters apart instead of the default of 8 (enables -a option). 

/* the -t option with numerical value 
   2 forces to change the spaces
   into tabs of only 2 characters */
$unexpand -t2 kt.txt>dv.txt

• -t, – -tabs=LIST option : This option uses comma separated LIST of tab positions (enables -a option).
• – -help option : This display a help message and exit.
• – -version option : This display version information and exit.

Also see : expand command  

To convert the leading spaces and tabs into tabs, there exists a command line utility called unexpand command. 

The unexpand command by default convert each spaces into tabs writing the produced output to the standard output. Here’s the syntax of unexpand command : 
Syntax : 

$unexpand [OPTION]... [FILE]...

where, OPTION refers to the options compatible with unexpand and FILE refers to the file name.