bash merge files by matching columns

Question

I do have two files:

 File1

 12    abc
 34    cde
 42    dfg
 11    df
 9     e   


 File2

 23    abc
 24    gjr
 12    dfg
 8     df

I

Answer 1

Since I was testing with bash 3.2 running as sh (which does not have process substitution as sh), I used two temporary files to get the data ready for use with join:

$ sort -k2b File2 > f2.sort
$ sort -k2b File1 > f1.sort
$ cat f1.sort
12    abc
34    cde
11    df
42    dfg
9     e  
$ cat f2.sort
23    abc
8     df
12    dfg
24    gjr
$ join -1 2 -2 2 -o 1.1,2.1,0 -a 1 -a 2 -e NA f1.sort f2.sort
12 23 abc
34 NA cde
11 8 df
42 12 dfg
9 NA e
NA 24 gjr
$

With process substitution, you could write:

join -1 2 -2 2 -o 1.1,2.1,0 -a 1 -a 2 -e NA <(sort -k2b File1) <(sort -k2b File2)

If you want the data formatted differently, use awk to post-process the output:

$ join -1 2 -2 2 -o 1.1,2.1,0 -a 1 -a 2 -e NA f1.sort f2.sort |
> awk '{ printf "%-5s %-5s %s\n", $1, $2, $3 }'
12    23    abc
34    NA    cde
11    8     df
42    12    dfg
9     NA    e
NA    24    gjr
$