Replace whitespaces with tabs in linux

Solution 1:

Use the unexpand(1) program

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'').

Solution 2:

I think you can try with awk

awk -v OFS="\t" '$1=$1' file1

or SED if you preffer

sed 's/[:blank:]+/,/g' thefile.txt > the_modified_copy.txt

or even tr

tr -s '\t' < thefile.txt | tr '\t' ' ' > the_modified_copy.txt

or a simplified version of the tr solution sugested by Sam Bisbee

tr ' ' \\t < someFile > someFile

Solution 3:

Using Perl:

perl -p -i -e 's/ /\t/g' file.txt