Positive lookbehind regex obvious maximum length

Question

So I have been experimenting with regex in order to parse the following strings:

INFO: Device 6: Time 20.11.2015 06:28:00 - [Script] FunFehlerButton: Execute [0031 text]    
and    
INFO: Device 0: Time 09.12.2015 03:51:44 - [Replication] FunFehlerButton: Execute    
and    
INFO: Device 6: Time 20.11.2015 06:28:00 - FunFehlerButton: Execute

The regex I tried to use are:

(?<=\\d{1,2}:\\d{2}:\\d{2} - ).*

and

(?<=\\[\\w*\\]).*

of which the first one runs correctly and the second one lands in a expcetion.

My goal is to get the text "FunFehlerButton: Execute ...".

I hope someone can hint me in the right direction.

Hey, there is the page [txt2re](http://txt2re.com/) where you can create regex from a string. — Graphican0, Jan 05 '16 at 16:28
Check http://stackoverflow.com/questions/9030305/regular-expression-lookbehind-doesnt-work-with-quantifiers-or — trincot, Jan 05 '16 at 16:32

score 1 · Answer 1 · answered Jan 05 '16 at 16:33

1

Java doesn't support variable length expression in lookbehind.

You can instead use this regex:

String re = "(?:\\d{2}:\\d{2}:\\d{2} - (?:\\[[^\\]]*\\] )?)([\\w: -]+)";

And use captured group #1

RegEx Demo

answered Jan 05 '16 at 16:33

anubhava

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score 1 · Accepted Answer · answered Jan 05 '16 at 16:49

Java supports variable length lookbehind only if the size is limited and the subpattern in the lookbehind isn't too complicated.

In short, you can't write:

(?<=\\[\\w*\\]).*

But you can write:

(?<=\\[\\w{0,1000}\\]).*

However something like:

(?<=\\[(?:\\w{0,2}){0,500}\\w?\\]).*

doesn't work since the max length isn't obvious.

Positive lookbehind regex obvious maximum length

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