Regex to match a string not followed by some string

Question

I have a string block as below

1. While #EngineSpeed$b4tgup#
2. While #AcceleratorPedal$desddd# <=2
3. While #AcceleratorPeda@$desddd# <=2
4. While #AcceleratorPe#al$desddd# <=2
5. While #AcceleratorP@dal$desddd# <=2
6. While #AcceleratorPeda l$desddd# <=2
7. 设置 #AcceleratorPedal$y6qs8m#=@AcceleratorPedal+0.06
8. 设置 #WaitStart$jhx0vu#=11
9. 设置 #WaitStart$jhx0vu#^11
10. 设置 #WaitStart$jhx0vu#_11
11. 设置 #WaitStart$jhx0vu#-11
12. 设置 #AcceleratorQuora$yd6ba3#=1
13. 设置 #AcceleratorQuora$yd6bd3#=1
14.
15. Check #EnginePower#
16. While #EngineSpeed
17. set #WaitStart
18. set #WaitStart<13
19. set #WaitStart<=13
20. set #WaitStart <= 13

Now I want to have a regex to match a substring starts with # but not followed by # or not followed by a substring like this $\w{6}#.

So in the string block above only line 16,17,18,19,20 match,in line 16 the result is #EngineSpeed,in line 17 the result is #WaitStart,the others are not match, in line 20 ,the result is also #WaitStart, it followed by <= 13,not followed by # or $\w{6}#,so it's also match!

For example,in line 15 the string is Check #EnginePower#,it starts with #,but it followed by #,in line 13 the string is 设置 #AcceleratorQuora$yd6bd3#=1,it starts with #,but followed by a substring like $\w{6}#.

I have wrote a regex like this #\w+(?<!#|$\w{6}#),but the test result in RegexBuddy is shown in the picture below,almost every line is match,it doesn't meet my requirement,how can I can modify the regex? Thanks in advance!

I believe that OP didn't express his thoughts well. Title is misleading. Vote to reopen. — revo, Jul 12 '16 at 13:28
Oh my god,this guys don't read my questions carefully and they mark it as a duplicate question careless! — flyingfox, Jul 12 '16 at 15:21
Why should line 17 match start with **set** ? You said, you want strings that start with `#`. So, why is it different than line 16? What's the rule that distinguishes between these two? — Tamas Rev, Jul 12 '16 at 19:07
@TamasRev ,I said a string not a line,so the substring in line 17 is okay — flyingfox, Jul 13 '16 at 01:46

Wiktor Stribiżew · Accepted Answer · 2016-07-13T06:56:13.810

3

From all the strings above you want to match

While #EngineSpeed

set #WaitStart

set #WaitStart<13

set #WaitStart<=13

set #WaitStart <= 13

You can use

(?<=\s)#\w+(?!.*[@$#])

See this regex demo

Details:

(?<=\s) - there must be a whitespace before...
# - a literal hash
\w+ - 1 or more word chars
(?!.*[@$#]) - fail the match if there are @, or $, or # somewhere after the \w+ on the line.

edited Jul 13 '16 at 06:56

answered Jul 12 '16 at 19:18

Wiktor Stribiżew

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thanks a lot,I have updated my question, now if I also want to mach a string like this **set #WaitStart <= 13**, how can I modify your regex,I found your regex only match a substring not followed by anything! – flyingfox Jul 13 '16 at 03:01
Now I have wrote a regex for myself `\s#\w+(?![@\w\$#_])`,but thank you all the same! Shall I need to vote your answer for the right answer due to your patient? – flyingfox Jul 13 '16 at 06:43
I do not understand how `\s#\w+(?![@\w\$#_])` can work for you since it matches in `6. While #AcceleratorPeda l$desddd# <=2` (see [demo](https://regex101.com/r/rN3mP9/6)). If my answer proved helpful, please consider upvoting, if it worked for you, consider accepting (these are usual SO rules). – Wiktor Stribiżew Jul 13 '16 at 06:52
Ah, I did not get your update. You do not want the `<=` + digits in the match, right? I updated the answer. – Wiktor Stribiżew Jul 13 '16 at 06:53
I was battling this in Ruby, and the `[]` were the key to unlock why it wasn't working. (I was pushing forward with `(?!\S)` and so-on) – joshfindit May 05 '20 at 19:10
@joshfindit Well, I have no idea what you actually need, but from today's perspective, my solution for the current OP problem should be `(?<!\S)#(?!.*[@$#])\w+` ([demo](https://regex101.com/r/rN3mP9/15)). – Wiktor Stribiżew May 05 '20 at 20:22

Regex to match a string not followed by some string

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