Notepad++: Add leading zero(s) to lines but up to 9 digits
Solution 1:
Adapted from Leading Zeros on Notepad++ community forum:

Find what:
^(\d{9})(\d{8})(\d{7})(\d{6})(\d{5})(\d{4})(\d{3})(\d{2})(\d)$

Replace with:
(?{1}\1)(?{2}0\2)(?{3}00\3)(?{4}000\4)(?{5}0000\5)(?{6}00000\6)(?{7}000000\7)(?{8}0000000\8)(?{9}00000000\9)
Solution 2:
This can be done in two steps:
First, prefix all lines with zeroes so all lines contain at least 9 digits:
Search: ^
Replace: 000000000
[x] Regular expression
[ ] . matches newline
^
means: The beginning of a line
Second, use this regex to cut off excess zeroes from the beginning of all lines:
Search: ^0*(\d{9})$
Replace: \1
The search regex means: Find lines that start with any number of zeroes 0*
, followed by exactly 9 digits \d{9}
before the end of the line $
. The 9 digits are marked as a group ( )
which can be referenced in the replace box as \1
. The entire match (i.e. the whole line) will be replaced with the contents of this group.