Let's create a space delimited file:
tommy@tommy-ThinkPad-T420:~$ cat > new.txt
chr1 100 200
chr2 300 400
chr3 240 700
ctrl + D to indicate cat that this is the last line.
use awk:
tommy@tommy-ThinkPad-T420:~$ cat new.txt | awk -F ' ' '{print $1"\t"$2"\t"$3}'
chr1 100 200
chr2 300 400
chr3 240 700
use sed:
tommy@tommy-ThinkPad-T420:~$ cat new.txt | sed 's/ /\t/g'
chr1 100 200
chr2 300 400
chr3 240 700
use tr :
tommy@tommy-ThinkPad-T420:~$ cat new.txt | tr ' ' '\t'
chr1 100 200
chr2 300 400
chr3 240 700
tommy@tommy-ThinkPad-T420:~$ rm new.txt
you can redirect the newly generated tab delimited file to a new file
tommy@tommy-ThinkPad-T420:~$ cat new.txt | tr ' ' '\t' > new1.txt
Linux commands are so cool!