How to loop through, match and replace?

Question

I have multiple strings with same curly braces I want to replace them as dynamic if I get the count as 1 then need to replace the first occurrence, If count as 2 then replaces t

Answer 1

There are a few issues with your code, you need to ensure that the variable in the preg_match_all() is the string your trying to search.

But the main problem is in the replacement part. You need to replace the current match value ($match) and replace it in a new string - currently you always replace the new match in the original string. Here I create $NewValue from the original string and keep replacing values in that...

if(preg_match_all("/\{\{[^{}]+\}\}/", $String, $matches)) {
    $NewValue = $String;
    foreach ($matches[0] as $match) {
        $Count++;
        $Query = "SELECT link FROM student WHERE linkVal = '".$match."'";
        $Result = $con->query($Query);

        if($row = $Result->fetch(PDO::FETCH_ASSOC)) {
            $NewValue = preg_replace("/".preg_quote($match)."/", 
                              $row["link"], $NewValue);
        }
    }

    echo json_encode($NewValue);

}

You should also look into using prepared statements as currently you may be open to SQL Injection problems.

Answer 2

The expression we might wish to design here can be like one of these:

({{)(.+?)(}})

which is only using capturing groups ().

DEMO 1

---

(?:{{)(.+?)(?:}})

and here we can use non-capturing groups (?:), if we do not wish to keep the {{ and }}.

DEMO 2

Then, we could simply do the preg_replace that we wanted to do.

Test

$re = '/(?:{{)(.+?)(?:}})/m';
$str = '{{ONE}} {{TWO}} {{THREE}} {{FOUR}} {{FIVE}} {{SIX}}';
$subst = '$1';

$result = preg_replace($re, $subst, $str);

echo "The result of the substitution is ".$result;

Answer 3

Within the loop on each match, instead of using preg_replace, I suggest you to use str_replace:

if(preg_match_all("/\{\{[^{}]+\}\}/", $lclString, $matches)) {
    $NewValue = $String;
    foreach ($matches[0] as $match) {
        $Count++;
        $Query = "SELECT link FROM student WHERE linkVal = '".$match."'";
        $Result = $con->query($Query);

        if($row = $Result->fetch(PDO::FETCH_ASSOC)) {
            $NewValue = str_replace($match, $row["link"], $NewValue);
            //          ^^^^^^^^^^^^^^^^^^
        }
    }
    echo json_encode($NewValue);
} 

Answer 4

You can use preg_replace_callback to iterate through your matches.

e.g.

$str = "{{ONE}} {{TWO}} {{THREE}} {{FOUR}} {{FIVE}} {{SIX}}";
$replaced = preg_replace_callback('/{{([^{}]*)}}/', function($match) {
// $match[1] contains the current match (first capture group) e.g. ONE
// return your replacement for the current match, e.g. reversed string ENO
return strrev($match[1]);
}, $str);
echo $replaced;

Output will be ENO OWT EERHT RUOF EVIF XIS

Answer 5

You can greatly simplify your code by fetching all the replacement values in one query:

$String = "{{ONE}} {{TWO}} {{THREE}} {{FOUR}} {{FIVE}} {{SIX}}";
if(preg_match_all("/\{\{[^{}]+\}\}/", $String, $matches)) {
    $Query = "SELECT linkVal, link FROM student WHERE linkVal IN('".implode("','", $matches[0])."')";
    $Result = $con->query($Query);
    if ($rows = $Result->fetchAll(PDO::FETCH_ASSOC)) {
        $NewValue = str_replace(array_column($rows, 'linkVal'), array_column($rows, 'link'), $String);
    }
    echo json_encode($NewValue);
}