CODEWITHSUNDEEP
regex
Michael Plautz
Michael Plautz

Reputation: 3778

Regex include optional group with repeated match all group

So here's my quandary:

^.*System(.*)(\d{4}-\d{2}-\d{2})?\.log

I need a regular expression that will match this optional group in parentheses (a date). However, since this group is optional, and the .+ is "eager", the date group never participates in the match. So I am trying to match things like these:

/var/log/ws/SystemOut.appserver204.log
/var/log/ws/SystemOut.appserver204.2014-10-22.log
/var/log/ws/SystemErr.appserver208.log
/var/log/ws/SystemErr.appserver212.2014-11-12.log

However, the first group, (.+), always takes everything up until the .log, resulting in the optional date group never participating in the match. If I don't make the group optional, I start including the date, but then two of those cases mentioned above don't get matched.

How can I do what I am trying to accomplish? (For reference purposes, I am working in Java.)

Upvotes: 0

Views: 60

Answers (3)

hwnd
hwnd

Reputation: 70732

* is a greedy operator meaning it will match as much as it can and still allow the remainder of the regular expression to match. Use *? for a non-greedy match meaning "zero or more — preferably as few as possible". 

^.*System.*?(\d{4}-\d{2}-\d{2})?\.log

Live Demo

Upvotes: 1

Bas
Bas

Reputation: 27095

Look at this sample. The regex ^.*System(.+?)\.?(\d{4}-\d{2}-\d{2})?\.log matches the text in Group 1 and the date in Group 2 (excluding the dot). A visualization:

Regex visualization

Upvotes: 0

Khanna111
Khanna111

Reputation: 3913

^.*System.*\.(\d\d\d\d-\d\d-\d\d)\.log$

Should do it.

Upvotes: 0

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