Pls need advice on forging custom diclists

[bigblacknose]

What is the easiest way to do such operations :
1-pick all 8 chars long words from a list file and create a new one with them only.
2- append a couple predefined pre or suffix to these words (123, 111, 007 for example)

I would rather do this in a linux terminal but i dont mind using a  windows gui app.

Thank you, any help is greatly appreciated.

Check this out:
https://hashcat.net/wiki/doku.php?id=hashcat_utils#len

And this:
https://hashcat.net/wiki/doku.php?id=rule_based_attack

Or this:

cat your_dict.txt | awk 'length()==8' > new_dict.txt
for i in `cat new_dict.txt`; do echo ${i}123 >> new_dict123.txt; done

Google for other solutions.