Regular expression Surround

1, look around is to see the meaning of the surrounding. Look around to match a location where some conditions are met. That is, the front and back of the location, containing some content, which does not contain some content.

2, for 12345678, modified to 12,345,678. The need to do this is to add a comma in some places in the number, which is characterized by a comma at the position of the rightmost number, and a three-digit multiple. As follows:

Replace with find (? <=\d) (? = (\d\d\d) + ([^\d]|$)), which means find a location, replace with,

(? <=\d) There's a number on the left.

(? = (\d\d\d) + ([^\d]|$)) has a multiple of three digits to the right, and the rightmost is not a number, or a line end.

You can also use (? <=\d) (? = (\d\d\d) + (?! \d)), (?! \d) indicates that the right is not a number.

Regular expression Surround