Check for a specific suffix by RegEx and select entire match including suffix

Question

First of all, this is my first question in the community hence please pardon my wrongs Experts! I am learning regex and faced a scenario where I am failing to create answer by myself.

Let's say if there is humongous paragraph, can we first match on the basis of a specific suffix (say '%') and Only then go back and select the desired logic including suffix?

eg part of the text is "abcd efghMNP 0.40 % ijkl mnopSNP -3.20 % xyz". Now in this, if you notice - and I got this much - that there is pattern like

/([MS]NP[\s\d\.-%]+)/

I want to replace "MNP 0.40 %" or "SNP -3.20 %" with blank. replacing part seems easy :) But the problem is with all my learning I am not able to select desired ONLY IF there exists a '%' at the end of match.

The sequence of match I wish to reach at is -- if suffix '%' exists, then match the previous pattern, and if successful then select everything including suffix and replace with empty.

Answer 1

There are several expressions that would do so, for instance this one with added constraints:

[A-Z]{3}\s+[-+]?[0-9.]+\s*%

Test

 const regex = /[AZ]{3}\\s+[-+]?[0-9.]+\\s*%/gm; const str = `abcd efghMNP 0.40 % ijkl mnopSNP -3.20 % xyz "MNP 0.40 %" or "SNP -3.20 %"`; const subst = ``; // The substituted value will be contained in the result variable const result = str.replace(regex, subst); console.log(result); 

Demo 1

Or a simplified version would be:

[A-Z]{3}(.*?)%

Demo 2

Answer 2

You can not go back in the matching if you have encountered a suffix % , but what you can do is to make it part of the pattern so that is has to be matched.

In Javascript you could perform a zero length lookahead assertion (?= making sure that what is on the right contains a pattern or in this case a % but that will not be a real benefit in this case as you want it to be part of the match.

A bit more specific match could be:

[MS]NP\s*-?\d+(?:\.\d+)?\s*%

• [MS]NP Match M or S followed by NP
• \\s*-? Match 0+ times a whitespace char followed by an optional -
• \\d+(?:\\.\\d+)? Match 1+ digits followed by an optional part to match a dot and 1+ digits
• \\s*% Match 0+ whitespace chars followed by matching %

Regex demo

Answer 3

Use regular expressions with non-capturing parentheses , like so:

string = 'example string with an intended nested string to match.';
regexp = /(?:intended)(.*)(?:to match)/;
firstMatch = regexp.exec(string)[1]; // " nested string "

The question mark has several uses in regular expressions, the parentheses question mark colon form (?:more regex) is the non-capturing parentheses .

See MDN for more details of exec() , string.match() , and regular expressions.