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regexnegative-lookbehind

How to regex with negative search?

I want to search a document for the following string

<whoName>[substring]</whoName>

where substring != "self"

so 

<whoName>other</whoName>

would pass.

but 

<whoName>self</whoName>

would fail

Solution

  • You can use this negative lookahead based regex:

    <(whoName)>(?!self\s*<).*?<\/\1>

    RegEx Demo

    Regex breakup:

    <(whoName)>  # Match <whoName> and capture it ($1)
(?!self\s*<) # Negative lookahead that means current position is not followed by literal 
             # self followed by 0 or more spaces and <
.*?          # Match 0 or more characters (non-greedy)
<\/\1>       # Match closing tag using back-reference to captured group #1