'Regex to match string between %

I'm trying to match substrings that are enclosed in %'s but preg_match_all seems to include several at the same time in the same line.

Code looks like this:

preg_match_all("/%.*%/", "%hey%_thereyou're_a%rockstar%\nyo%there%", $matches);
print_r($matches);

Which produces the following output.

Array
(
    [0] => Array
        (
            [0] => %hey%_thereyou're_a%rockstar%
            [1] => %there%
        )

)

However I'd like it to produce the following array instead:

[0] => %hey%
[1] => %rockstar%
[2] => %there%

What am I missing?

phpregexpreg-match-all


Solution 1:[1]

You're doing a greedy match - use ? to make it ungreedy:

/%.*?%/

If a newline can occur inside the match, add the s (DOTALL) modifier:

/%.*?%/s

Solution 2:[2]

Add a ? after the *:

preg_match_all("/%.*?%/", "%hey%_thereyou're_a%rockstar%\nyo%there%", $matches);

Solution 3:[3]

The reason is that the star is greedy. That is, the star causes the regex engine to repeat the preceding token as often as possible. You should try .*? instead.

Solution 4:[4]

You could try /%[^%]+%/ - this means in between the percent signs you only want to match characters which are not percent signs.

You could also maybe make the pattern ungreedy, e.g. /%.+%/U, so it will capture as little as possible (I think).

Solution 5:[5]

|%(\w+)%| This will work exactly what do you want.

Solution 6:[6]

While the solution is to turn a greedy .* into a lazy .*? (or replace .* with [^%]*), you might also want to actually get rid of % symbols in the output.

In that case, you will need to use a capturing group and get $matches[1] if a match occurred:

$str = "%hey%_thereyou're_a%rockstar%\nyo%there%";
if (preg_match_all("/%([^%]*)%/", $str, $matches)) {
    print_r($matches[1]);
}
// => Array( [0] => hey [1] => rockstar [2] => there )

Note that print_r($matches[0]); will output full matches, // => Array( [0] => %hey% [1] => %rockstar% [2] => %there% ). The [^%] pattern is a negated character class that matches any char other than a % char.

See the PHP demo.

Variations

If you need to make sure there are only letters, digits or underscores between % chars, you can use

"/%(\w*)%/"

If you want to match any chars other than % and whitespace between two % chars use

"/%([^\s%]*)%/"

The [^\s%]* pattern is a regex that matches any zero or more chars other than whitespace (\s) and a % char.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Greg
Solution 2 Alix Axel
Solution 3 fresskoma
Solution 4 Tom Haigh
Solution 5
Solution 6 Wiktor Stribiżew

Related Questions