Read specific line from files

[zzari]

Hi everybody, this is my first time using Tcl/Tk and i have a problem working on a txt file.
My input file is a mix of word and numbers in this way:
- the first 5 lines are words
- a various number of lines of numbers (2 column for each line)
- last 6 lines of words.

example:

aaaaaaaaaaaaaa
bbbbbbbbbbbbbbb
ccdcccccccccccccc
ddddddddddddddd
eeeeeeeeeeeeee
1 2
3 4
5 6
8 9
aaaaaaaaaaaaaaaa
ddddddddddddddd
fffffffffffffffff
rrrrrrrrrrrrr
ggggggggggggggggggg
hhhhhhhhhhhhhhh

I want to read and copy on a new file just only the numbers.
Is there anyone that could help me with a simple code?
txs in advance