CODEWITHSUNDEEP
regexpcre
Suresh
Suresh

Reputation: 1091

Regex match with negative look ahead and non greedy

source string

<html name="abc:///Testers/something.txt" in="abc/Testers/something.txt" loci="123" sap="abcdefgh="/><html name="abc:///needed.txt" src="abc/needed.txt" location="123" sap="rtyghu"/><html name="abc:///Testers/Testers3/Another.txt" in="abc/Testers/Testers3/Another.txt" loci="123" sap="jhkiopjhg"/><html name="abc:///onemore.txt" src="abc/onemore.txt" location="123" sap="dfrtyu"/>

How do I match the section starting from <html name=" not followed by (needed) or (onemore) and ending with />

So in this string there should be two matches which are

<html name="abc:///Testers/something.txt" in="abc/Testers/something.txt" loci="123" sap="abcdefgh="/>
<html name="abc:///Testers/Testers3/Another.txt" in="abc/Testers/Testers3/Another.txt" loci="123" sap="jhkiopjhg"/>

I tried this - <html name=(?!(needed|onemore)).*?"\/>

It doesnt work as I am confused with the non greedy and negative lookahead stuffs.

Upvotes: 1

Views: 2740

Answers (2)

Tezra
Tezra

Reputation: 8833

Here is the breakdown of your regex <html name=(?!(needed|onemore)).*?"\/>

<html name=(?!(needed|onemore)).*?"\/>
1) Literal match: <html name=
2) Not followed by: "needed" or "onemore"
3) Lazy grab all: .*?
  Until Literal match: "/>

What you need to do is check for needed or onemore with each character grab using another grouping like this <html name=(?:(?!(needed|onemore)).)*?"\/>. That will check that "needed" or "onemore" isn't next on each character grab. (I would also recommend using [^>] instead of . so that you don't need the lazy quantifier.)

However, I would recommend using something like this for your filtering <html name=([^>no]|n(?!eeded)|o(?!nemore))*>. Much easier to adapt and less work for the regex engine.

Upvotes: 2

revo
revo

Reputation: 48711

What you need is to use a repetition quantifier in addition to putting a restriction on where it should give up traversing:

<html\s+name="(?![^"]*(?:needed|onemore))[^>]*>

Live demo

Upvotes: 4

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