字符串之后没有空格的正则表达式OR语句将无效

Question

I am trying to get this regex to match (once or twice) any occurrence of these strings: border-box|padding-box|content-box

Here is the regex:

((?:border-box|padding-box|content-box){1,2})

Here is the sample string:

background: url("my image.jpg") left right 2px 50% 75% repeat-x round scroll border-box padding-box;

Expected result:

border-box padding-box

Actual result:

Array
(
    [0] => border-box
    [1] => border-box
)

Oh and btw I am using this site to test my regex: http://www.phpliveregex.com/ Note: I am using preg_match not preg_match_all

Answer 1

The problem is that your pattern requires the repetitions to occur immediately after each other, with no whitespace between.

Try adding a \s* after the alternation to allow for optional whitespace between the repetitions, like this:

(?:(?:border-box|padding-box|content-box)\s*){1,2}

Or even better:

(?:(?:border|padding|content)-box\s*){1,2}

Note that because of the *, this will also match a string like border-boxborder-box (no whitespace between repetitions). If this is a problem you can try a pattern like this:

(?:(?:border|padding|content)-box)(?:\s+(?:border|padding|content)-box)?

Note that I've removed the surrounding (…) since this group would always be identical to the entire match, so it's almost certainly not necessary.