syntax
$ unexpand [OPTION] [FILE]
To convert blanks in a file to tabs and write the output to stdout
$ unexpand sample.txt
To write the output to a file
$ unexpand sample.txt > unexpand_output.txt
To convert blanks to tabs, reading from standard output
$ unexpand
To convert all blanks, instead of just initial blanks
$ unexpand -a sample.txt
To convert only leading sequences of blanks
$ unexpand --first-only sample.txt
To have tabs a certain number of characters apart
$ unexpand -t 4 sample.txt
To mention multiple tab positions
$ unexpand -t 5,10,15 sample.txt
regards,
T.Dhanasekar