Replace with dynamic variable in preg_replace

Question

I'm getting stuck at this problem, which is

I have an array like this:

$array = [
    'name' => 'John',
    'email' => [email protected]
];

And a string sample like this:

$string = 'Hi [[name]], your email is [[email]]';

The problem is obvious, replace name with John and email with [email protected].

What i attempted:

//check if $string has [[ ]] pattern

$stringHasBrackets = preg_match_all('/\[\[(.*?)\]\]/i', $string,  $matchOutput);

if ($stringHasBrackets) {

    foreach ($matchOutput[1] as $matchOutputKey => $stringToBeReplaced) {

        if (array_key_exists($stringToBeReplaced, $array)) {

            $newString = preg_replace("/\[\[(.+?)\]\]/i",
                            $array[$stringToBeReplaced],
                            $string);

        }
    }
}

Which led me to a new string like this:

Hi [email protected], your email is [email protected]

Makes sense because that's what the pattern is for, but not what I wanted.

How can I solve this? I thought of using a variable in the pattern but don't know how to do it. I've read about preg_replace_callback but also don't really know how to implement it.

Thanks!

Wiktor Stribiżew · Accepted Answer · 2018-08-21 11:18:45Z

4

You may use preg_replace_callback like this:

$array = ['name' => 'John', 'email' => '[email protected]'];
$string = 'Hi [[name]], your email is [[email]]';
echo preg_replace_callback('/\[\[(.*?)]]/', function ($m) use ($array) {
        return isset($array[$m[1]]) ? $array[$m[1]] : $m[0]; 
    }, $string);

See PHP demo.

Details

'/\[\[(.*?)]]/' matches [[...]] substrings putting what is inside the brackets into Group 1
$m holds the match object
use ($array) allows the callback to access $array variable
isset($array[$m[1]]) checks if there is a value corresponding to the found key in the $array variable. If it is found, the value is returned, else, the found match is pasted back.

answered Aug 21, 2018 at 11:18

Wiktor Stribiżew

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4 Comments

Raymond Nijland Over a year ago

Nice answer +1 @DuongNguyen But because running regex is pretty expensive operation . i would include a if to check if the string contains a replace templates checking on [[ and ]] see demo ideone.com/K4hKmJ .. Nicer would be offcource to make a function

Duong Nguyen Over a year ago

Thanks. Will do a research on preg_replace_callback and get back to you if this works. @RaymondNijland I checked the string with preg_match_all, is it alright?

Raymond Nijland Over a year ago

"I checked the string with preg_match_all, is it alright?" @DuongNguyen preg_match_all still uses regexes now you start up two regex engines.

Duong Nguyen Over a year ago

@RaymondNijland I see.

anubhava · Accepted Answer · 2018-08-21 16:27:30Z

3

preg_replace accepts arrays as regex and replacement so you can use this simpler approach:

$array = ['name' => 'John', 'email' => '[email protected]'];
$string = 'Hi [[name]], your email is [[email]]';

// create array of regex using array keys
$rearr = array_map(function($k) { return '/\[\[' . $k . ']]/'; },
         array_keys($array));

# pass 2 arrays to preg_replace
echo preg_replace($rearr, $array, $string) . '\n';

Output:

Hi John, your email is [email protected]

PHP Code Demo

edited Aug 21, 2018 at 16:27

answered Aug 21, 2018 at 11:16

anubhava

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3 Comments

Duong Nguyen Over a year ago

Gotta do another research on using array_map :D

anubhava Over a year ago

array_map is used to convert each key into regex. So name becomes /\[\name]]/

anubhava Over a year ago

@bobblebubble: You're right, array_values isn't needed.

Yogesh Salvi · Accepted Answer · 2018-08-21 11:20:00Z

1

You can try this,

$array = ['name' => 'John', 'email' => '[email protected]'];
$string = 'Hi [[name]], your email is [[email]]';
$stringHasBrackets = preg_match_all('/\[\[(.*?)\]\]/i', $string,  $matchOutput);

if ($stringHasBrackets) {
    $newString = $string;
    foreach ($matchOutput[1] as $matchOutputKey => $stringToBeReplaced) {
        if (array_key_exists($stringToBeReplaced, $array)) {
            $newString = preg_replace("/\[\[$stringToBeReplaced\]\]/i", $array[$stringToBeReplaced], $newString);
        }
    }
    echo $newString;
}

answered Aug 21, 2018 at 11:20

Yogesh Salvi

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2 Comments

Duong Nguyen Over a year ago

Thanks! This works like a charm. I'm not a regex wizard but how did you know where to put the variable?

Yogesh Salvi Over a year ago

@DuongNguyen, Thanks :)

Agnius Vasiliauskas · Accepted Answer · 2018-08-21 13:01:32Z

1

I think here more simply would be to use str_replace function, like:

$array = [
          'name' => 'John',
          'email' => '[email protected]'
          ];

$string = 'Hi [[name]], your email is [[email]]';
$string = str_replace(array_map(function ($v) {return "[[{$v}]]";}, 
                      array_keys($array)), $array, $string);
echo $string;

Updated for $array to be "untouchable"

edited Aug 21, 2018 at 13:01

answered Aug 21, 2018 at 12:33

Agnius Vasiliauskas

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3 Comments

Duong Nguyen Over a year ago

This can be much simpler than using regex, but I'm not allowed to touch the array, and array_keys returns an array, so can I somehow concatenate [[ and ]] to it? Also, I want to replace array_keys($array) in the string with array values.

Agnius Vasiliauskas Over a year ago

see updated version - in this case we need array_map also. And yes - it searches in string for modified keys and replaces with array values

Duong Nguyen Over a year ago

Thank you Agnius!

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