Regex match everything from the last occurrence of either keyword

问题

I'm trying to match everything from the last occurrence of either keyword (foo or bar) to the end of the string.

Example (a):

// I want to match ' foo do you?';
$source = 'This is foo and this is bar i like foo do you?';
$pattern = '/pattern/';
preg_match($pattern, $source, $matches);

I tried the following:

$pattern = '/( (foo|bar) .*)$/';

Thinking it would match the last occurrence of foo and all the following text, but it instead matches the first occurrence.

print_r($matches);

/*
Array
(
    [0] =>  foo and this is bar i like foo do you?
    [1] =>  foo and this is bar i like foo do you?
    [2] => foo
)
*/

Note I'm concerned with the theory and reasoning of how to do this, so please add some explanation or a link to to the relevant explanation, please.

回答1:

.+((foo|bar).+)$

.+ matches many characters up front.

((foo|bar) matches and captures your keyword(s).

.+) matches and captures many characters.

$ matches the end of the string/line.

Using your example:

This is foo and this is bar i like foo do you?
                                   ^---------^

回答2:

Use a greedy match up front to consume as much of the haystack as you can before your pattern:

>>> import re
>>> source = 'This is foo and this is bar i like foo do you?'
>>> pattern = '.*((?:foo|bar).*)'
>>> re.search(pattern, source).groups()[0]
'foo do you?'

A grottier way of doing it is to use negative look-aheads:

>>> # Negative look-ahead for the pattern: (?!.*(?:foo|bar))
>>> pattern = '((?:foo|bar)(?!.*(?:foo|bar)).*)'
>>> re.search(pattern, source).groups()[0]
'foo do you?'

来源：https://stackoverflow.com/questions/5440194/regex-match-everything-from-the-last-occurrence-of-either-keyword