如何仅在单行上匹配正则表达式？

Question

I have the following regex and sample input:

http://regex101.com/r/xK9dE3

As you can see it matching the first "yo". I only want the pattern to match on the same line (the second "yo") pattern with "cut me".

How can I make sure that the regex match is only on the same line?

Output:

Hi

Expected Output (this is what I really want):

Hi

yo keep this here

Keep this here

Answer 1

You can use this regex with s (DOTALL) regex flag:

^.*?(?=yo\b[^\n]*cut me:)

Online Demo: http://regex101.com/r/oV3eP7

yo\\b[^\\n]*cut me: is lookahead pattern that makes sure that yo with word boundary and cut me: are matched in the same line.

Answer 2

Remove the s or DOTALL flag and change your regex to the following:

^.*?((\yo\b.*?(cut me:)[\s\S]*))

With the DOTALL flag enabled . will match newline characters, so your match can span multiple lines including lines before yo or between yo and cut me . By removing this flag you can ensure that you only match the line with both yo and cut me , and then change the .* at the end to [\\s\\S]* which will match any character including newlines so that you can match to the end of the string.

http://regex101.com/r/sX2kL0

edit: Note that this takes a slightly different approach than the other answer, this will match the portion of the string that you want deleted so you can replace this portion with an empty string to remove it.