How to ignore a specific string while searching for a pattern in Regex?

Question

I have a query where I replace all the keywords specified in the pattern with the keyword enclosed in square brackets.

if my query already has Select [key] from table1, I should ignore and avoid replacing it:

var pattern = @"(?i)Key|IN|ON|VIEW";
var subject = "Select key from table1";
var result = Regex.Replace(subject, pattern, @"[$0]");

How to achieve this?

anubhava · Accepted Answer · 2014-08-27 12:21:11Z

2

You can use lookaheads to ignore matching [ and ] surrounding your keywords:

var pattern = @"(?i)(?<!\[)(?:Key|IN|ON|VIEW)(?!\])";

RegEx Demo

answered Aug 27, 2014 at 12:21

anubhava

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2 Comments

Jayaraman Over a year ago

Thanks Anubhav..it worked. but could you please tell me what does (?<![)(?: and (?!]) do.I din't get how it works.

anubhava Over a year ago

You're welcome. Link I provided has explanation of this regex on RHS. Also look at this very helpful article on lookarounds in regex: regular-expressions.info/lookaround.html

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