sort -m fails to merge >2 files

[Stephen Quan]

sort -m fails for files greater than two (2)
 
$ more 1 2 3
::::::::::::::
1
::::::::::::::
1
2
3
4
5
6
::::::::::::::
2
::::::::::::::
1
3
5
7
9
::::::::::::::
3
::::::::::::::
1
2
4
6
8
10
$ sort -m 1 2 3
1
1
1
2
2
3
3
4
4
5
5
6
6
7
8
10
9  <-------------------------------------------------------- out of sequence