Regex Quantifier on Alternatives(vertical bar "|")

Question

I want to trim a string if it starts and/or ends with foo or bar for example and want to get the inner string in a regex group.
For example

"fooTestbar" should be "Test",
"Test2bar" should be "Test2"
and "Test3" should be "Test3".

My current regex is:

^(foo|bar)?(.*)(foo|bar)?$

but this doesnt work, because I cant apply the Quantifier ? to the alternative group((foo|bar)).

My Code

static string returnMatch(string text){
string pattern = @"^(foo|bar)?(.*)(foo|bar)?$";
return System.Text.RegularExpressions.Regex.Match(text, pattern).Groups[2].Value;
}

Any help will be greatly appreciated.

Im using .Net`s System.Text.RegularExpressions.Regex.Match with C#, it didnt work. — Tearsdontfalls, Oct 30 '12 at 19:55

score 1 · Accepted Answer · edited Oct 30 '12 at 20:31

1

You can use this

^(?:foo|bar)?(.*?)(?:foo|bar)?$

You can now match it like this..

return Regex.Match(input,"^(?:foo|bar)?(.*?)(?:foo|bar)?$").Groups[1].Value;

edited Oct 30 '12 at 20:31

Tearsdontfalls

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answered Oct 30 '12 at 20:02

Anirudha

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Thank you, but this only worked for the beginning foo|bar, not for the and – Tearsdontfalls Oct 30 '12 at 20:09
Thanks, it worked so for me with a small editing, Regex.Matches doesnt have a replace Parameter. – Tearsdontfalls Oct 30 '12 at 20:16
Your regex solves this question, I dont need to do Regex.Matches, I can do only Regex.Match and I have the right result in Group 1. Thank you and all others for your help. – Tearsdontfalls Oct 30 '12 at 20:28

Ωmega · Answer 2 · 2012-10-30T20:17:38.557

1

I suggest you to go with

(?:^|(?<=^foo)).*?(?=bar$|$)

or, if you want to allow foo and/or bar at the beginning and at the end, then with

(?:^|(?<=^foo)|(?<=^bar)).*?(?=foo$|bar$|$)

having result in Groups[0]

edited Oct 30 '12 at 20:17

answered Oct 30 '12 at 20:04

Ωmega

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This replaces only the foo at the beginning, not for example a bar at the beginning and the replacing at the end doesnt work. – Tearsdontfalls Oct 30 '12 at 20:15
@Tearsdontfalls - I see no such example in your question... I have updated my answer with that alternative. – Ωmega Oct 30 '12 at 20:16
Ok, i explained it maybe a little bad, with your updated regex it only replaces foo|bar at the end. – Tearsdontfalls Oct 30 '12 at 20:22
@Tearsdontfalls - You must have some typo in your code, as my updated answer/solution should work properly. Check your code... – Ωmega Oct 30 '12 at 20:23

Regex Quantifier on Alternatives(vertical bar "|")

2 Answers2