How do I insert a specified statement at a specific place on each line?

I have a bunch of numbers
3235235
4657456
3454656
4636546
3435457
3463546
I want to insert after the third character of each line, order_no:
becomes
323 no.

Mar.07,2021

two powerful text processing tools under unix awk sed understand (not much research on,:) escape)
most programming languages can also be judged by regularity and logic


I can use notepadPP.

Menu