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Question

Answer 1

+1 A:

Try this:

^(?!system$)

Or this to match the whole line:

^(?!system$).*$

The regex has a negative look-ahead on its beginning, which doesn't match if "system" is the entire string.

Kobi 2010-06-03 09:28:03

Just out of curiosity, how does the ?! operator work? I've never used that one (though I've used pretty much regex I tend to find solutions which don't use 'not').

Alxandr 2010-06-03 09:30:24

Ahh, so simple! I'm sure I tried that...! Thankyou.

Kieron 2010-06-03 09:32:42

@Alxandr - it checks what follows your current position. For example, `c(?!4)` will match c from `Doc12`, but not the c on `Doc42`. A look-around doesn't capture, so I don't have to worry about replacing the digit, or check edge case (for example, if c were the last character: `Doc`).

Kobi 2010-06-03 09:36:18

Answer 2

+4 A:

Reject if it matches ^system$ (make sure i flag is ON).

Amarghosh 2010-06-03 09:29:36

This should be the first option, or course. I naturally (and possibly wrongly) assumed the OP cannot do it.

Kobi 2010-06-03 09:32:35

Answer 3

+1 A:

^$|^.{1-5}$|.{7}|^[^s]|^.[^y]|^..[^s]|^...[^t]|[^e].$|[^m]$

But use amarghosh's answer if you can.

(updated as per suggestion below)

Steve Bennett 2010-06-03 09:41:49

You probably meant `.{1,5}`.

Kobi 2010-06-03 09:46:17

heh, I wrote that without testing it. I'm kind of shocked that it actually worked first try. The first two clauses are redundant though, so: (^.{1-6}$)|(.{8})|(^[^s])|(^.[^y])|(^..[^s])|(^...[^t])|([^e].$)|([^m]$)Nice tip about ?! though - I hadn't heard of it.

Steve Bennett 2010-06-03 09:46:36

oops. that regex lets through "systuem". (and fails on empty string, which is apparently acceptable?)try:^$|^.{1-5}$|.{7}|^[^s]|^.[^y]|^..[^s]|^...[^t]|[^e].$|[^m]$

Steve Bennett 2010-06-03 09:51:23

Steve - Welcome to stack overflow. It is best to update your answer than to add another one as a comment. Also, start the regex line with 4 spaces - it will format it as code.

Kobi 2010-06-03 09:56:49

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Regex not equal to string

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