Join

sort <no options> | join <no options> doesn't work:

Important: FILE1 and FILE2 must be sorted on the join fields.  E.g.,
use ` sort -k 1b,1 ' if `join' has no options, or use ` join -t  ' if
`sort' has no options.

So you could try:

sort flash_int_list.txt | join -t  finish_comm - > t1

or:

sort -k 1b,1 flash_int_list.txt | join finish_comm - > t1

[1]