Match string until a character is found, which is also contained in an optional field

Question

I have the following string:

string = "x OPTIONAL() y z(..., ...)"

Where OPTIONAL() is indeed optional, so the string may also be:

string = "x y z(..., ...)"

Using regular expressions, I want to match the string until the first one of these characters is found:

([{;=,

Beware that OPTIONAL() includes one of the characters above, but the search should not stop at OPTIONAL(.

So I would like to have:

x OPTIONAL() y z

Or:

x y z

I'm currently using:

re.search("[ \t\n\r\f\v]*(OPTIONAL\(\))?([^([{;=,]+)", string)

And the match properly stops at:

x y z

when OPTIONAL() is not in the string.

However, with OPTIONAL() in the string, the match stops at:

x OPTIONAL

Try [`^(?:OPTIONAL\(\)|[^([{;=,])+`](https://regex101.com/r/Wr4P2O/1) — Wiktor Stribiżew, Aug 23 '18 at 09:46
Yes, it does. Shouldn't this be an answer, so I can approve it? — HBv6, Aug 23 '18 at 11:32
I have [posted it with explanations](https://stackoverflow.com/a/51984867/3832970). — Wiktor Stribiżew, Aug 23 '18 at 11:36

score 1 · Answer 1 · answered Aug 23 '18 at 10:43

1

You can use a lookbehind to match ( only if it is preceded by OPTIONAL.

^(?:[^([{,;=]+|(?<=OPTIONAL)\()+

answered Aug 23 '18 at 10:43

bobble bubble

score 1 · Accepted Answer · answered Aug 23 '18 at 11:33

You may use

^(?:OPTIONAL\(\)|[^([{;=,])+

Details

^ - start of string
(?: - start of a non-capturing group that will match either
- OPTIONAL\(\) - an OPTIONAL() suibstring
- | - or
- [^([{;=,] - a negated character class that matches any char other thasn (, [, {, ;, =, ,
)+ - one or more times.

2 Answers2