I want to match all repeating spaces in a each line of the text excluding spaces around a specified character.

For example, if I want to find repeating spaces before # in this text

first    second third
first second    third
first    second #third

first second    #third
first second #    third
#    first second third

I am expecting to match multiple spaces in first 3 lines but not to have matches in last 3.

I have tried this: /(\S\s{2,})(?!\s*#)/g but that is also matching repeating spaces after # How to write a regex for this case?

CodePudding user response：

One possible solution with lookarounds:

(?<![#\s])\s\s (?![\s#])

The pattern will match any 2 spaces \s\s , that are:

• not preceeded by either space or # ((?<![#\s]))
• not followed by either space or # ((?![\s#]))

Check the demo here.

CodePudding user response：

You could match what you want to get out of the way, and keep in a group what you are looking for.

(\s*#\s*)|\s{2,}

Explanation

• (\s*#\s*) Capture in group 1 # between optional whitespace chars
• | Or
• \s{2,} Match 2 or more whitespace chars

Regex demo

There is no language tagged, but if for example you want to replace the repeating spaces in the first 3 lines with a single space, this is a JavaScript example where you check for group 1.

If it is present, the return it to keep that part unmodified, else replace the match with your replacement string.

Note that \s can also match newlines, therefore I have added dashes between the 2 parts for clarity.

const regex = /(\s*#\s*)|\s{2,}/g;
const str = `first    second third
first second    third
first    second #third
------------------------
first second    #third
first second #    third
#    first second third`;
console.log(str.replace(regex, (_, g1) => g1 || " "));