Question

Infile1:

1 a
3 c
4 d
6 f

Infile2:

1 a 
2 b
5 e
6 f
7 g
8 h

How do I join these files with the unix join command to get this output:

1 aa
2 b
3 c
4 d
5 e
6 ff
7 g 
8 h

Dogbanes answer worked but…
when I apply dogbanes answer on this file:

27  27
28  22
29  37
30  15
31  21
32  13
33  18
34  24

and this:

27  7
28  13
29  6
30  12
31  30
32  5
33  10
34  28

They don’t join:

27  27
27  7
28  13
28  22
29  37
29  6
30  12
30  15
31  21
31  30
32  13
32  5
33  10
33  18
34  24
34  28

The second scenario is tab delimited so I used -t \t

Answer 1

First sort both files. Then use join to join on the first field of both files. You also need to pipe the output through sed if you want to remove the space and thus convert a a into aa. This is shown below:

$ join -t " " -1 1 -2 1 -a 1 -a 2  <(sort file1) <(sort file2) | sed 's/ \([a-z]\) / \1/g'
1 aa
2 b
3 c
4 d
5 e
6 ff
7 g
8 h