file_1
123412341234etc   1000001
567856785678etc   5000001
...

file_2
123412341234etc   1000002
567856785678etc   5000002
...

file_3
123412341234etc   1000003
567856785678etc   5000003
...

munged output
1000001 1000002 1000003 ...
5000001 5000002 5000003 ...