Regex to increase or decrease last digit in line by one.

Reggy guy

So I want to know if there is a regex to increase or decrease the value of the last digit in a line by one.
Example:

Reg1ex234 >>>> Reg1ex235

I’ve seen several examples to change ALL the digits in a line, but not the last one. Is this possible by regex only?

Reggy guy

@guy038 I saw your reply https://community.notepad-plus-plus.org/topic/14884/regex-to-change-numbers-to-a-value-1-step-lower/2

Is this possible only for the last digit in the line via regex? Thank you!

Alan Kilborn

@Reggy-guy

If your intent is to only ever affect the last digit, then yes, perfectly possible. But…most people would expect a change of this sort to transform 2019 into 2020 (note that TWO digits changed!) and this is not a reasonable expectation from regex replacement.

However, if that’s acceptable, then a way to change the only the last digit appearing on a line to the next digit lower is to search for (?-s)^(.+)(?:(0)|(1)|(2)|(3)|(4)|(5)|(6)|(7)|(8)|(9)) and replace with \1(?{2}9)(?{3}0)(?{4}1)(?{5}2)(?{6}3)(?{7}4)(?{8}5)(?{9}6)(?{10}7)(?{11}8)

That borrows heavily from the other post you linked to. :-)

Reggy guy

Thank you very much @Alan-Kilborn . It will be enough to resolve my current problem :).

Reggy guy

@Alan-Kilborn Hello again, could you help me with the regex to do this to the first number in every line instead of last?

Alan Kilborn

@Reggy-guy said:

the regex to do this to the first number in every line instead of last

Deceptively simple, I think.

Just add a ? after the + in the earlier search expression.

Alan Kilborn

I should add that it works for this reason:

.+ :

.+ matches (one or more characters) as much as it can before moving on. Also known as the “maximum munch”. So given the pattern .+\d and the string-to-test as abc123def345 the .+ part would match abc123def34 because the ending 5 would satisfy the \d in the pattern.

.+? :

.+? matches (one or more characters) as little as possible before moving on. Also known as the “minimum munch”. With the pattern .+?\d and the same string-to-test, the .+? part would match abc because the following 1 would match the \d.