Lum – Merging/Combining 2 text files according to numeric field

You just need the column command, and tell it to use tabs to separate columns

paste file1 file2 | column -s $'\t' -t

To address the "empty cell" controversy, we just need the -n option to column:

$ paste <(echo foo; echo; echo barbarbar) <(seq 3) | column -s $'\t' -t
foo        1
2
barbarbar  3

$ paste <(echo foo; echo; echo barbarbar) <(seq 3) | column -s $'\t' -tn
foo        1
           2
barbarbar  3

My column man page indicates -n is a "Debian GNU/Linux extension." My Fedora system does not exhibit the empty cell problem: it appears to be derived from BSD and the man page says "Version 2.23 changed the -s option to be non-greedy"

That's pretty easy with awk:

awk 'NR==FNR{a[$1]=$2;next}{print $0,a[$1]}' file2 file1

First (when file2 is being read) we create an array a which stores second column from file2, indexed with first column. And then we print file1 adding value from an array.