Regular expression to match a standalone = character

Question

I'm trying to match a single standalone '=' character with a regular expression.

For example, for this code

if(y == 5 || x = 1) {
  Do something ...
}

I want to match to the single '=', and not the "==". I've tried a lot of combinations of regular expression strings but I still can't get a match on the correct position.

Why are you using regex to parse code? Unless this is a very simple tool, you'll want something more robust. — TartanLlama, Jun 30 '16 at 08:20
Look for a = that's neither preceded or followed by another =? — Kerrek SB, Jun 30 '16 at 08:20
If I use that particular method, it will match the second "=" in the "==" portion. — Thaddeus Jones, Jun 30 '16 at 08:22
you can read single character than compare '=' if is equal then read next and compare it '=' if is equal do nothing, otherwise do necessary process. — Halil İbrahim Oymacı, Jun 30 '16 at 08:25

score 4 · Accepted Answer · edited May 23 '17 at 11:44

4

You can achieve this by using a negative lookbehind and a positive lookahead:

(?<!=)=(?!=)

Example: https://regex101.com/r/uV5eC5/1

For more information about lookahead/lookbehind, read Regex lookahead, lookbehind and atomic groups

edited May 23 '17 at 11:44

Community

1
1

answered Jun 30 '16 at 08:21

eol

23,236
5
46
64

2

If your regex parser supports this. – JefGli Jun 30 '16 at 08:23
Thanks for linking the tool, this should work. I just have to convert it to the C++ regex syntax. – Thaddeus Jones Jun 30 '16 at 08:28
This would only work with Boost library or PCRE library. C++11 regex follows ECMAScript regex, which doesn't support look-behind. – nhahtdh Jun 30 '16 at 08:29

score 0 · Answer 2 · answered Jun 30 '16 at 08:26

0

fbo's solution certainly is more elegant, but if it needs to be done in JS, which doesn't have look-behinds, you could do it with

[^=]=[^=]

Since it appears to be code you're checking, there will always be a character before and after the =, and therefore this test that neither of them is another =.

answered Jun 30 '16 at 08:26

SamWhan

8,296
1
18
45

Both your answer and his worked after converting it to the C++ regex syntax. – Thaddeus Jones Jun 30 '16 at 08:30
1

Note that if you want to use replace afterwards, it would also replace the symbol before and the symbol after `=`. So, you could capture them as separate groups: `([^=])(=)([^=])` and then use `$1==$3` for the replace (assuming you want to replace `=` with `==`). – Maria Ivanova Jun 30 '16 at 08:35

Regular expression to match a standalone = character

2 Answers2