I want to append txt files to another, based on similarity of the file name.

Like banana11.txt to banana12.txt

The pair of txt file is in their individual folder:

banana banana11.txt banana12.txt
car car11.txt car12.txt
happy happy11.txt happy12.txt

All names in each folder are the same, except the number, which is at the end of the name (would be 11, 12, 13).

The file is more than 6,000, in 6,000 folders.

Thanks!

Source: Windows Questions