How to loop through, match and replace? - php

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 the second occurrence as so on until condition satisfies.
<?php
include_once("con.php");
$db = new Da();
$con = $db->con();
$String = "{{ONE}} {{TWO}} {{THREE}} {{FOUR}} {{FIVE}} {{SIX}}";
$Count = 1;
if(preg_match_all("/\{\{[^{}]+\}\}/", $lclString, $matches)) {
foreach ($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("/\{\{[^{}]+\}\}/", $row["link"], $String);
}
}
echo json_encode($NewValue);
}
?>
If first occurrence the {{ONE}} should replace with new value with $row["link"],
Secondly replace {{TWO}} With New value so on.

Answer 1

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 2

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);
}

Answer 3

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 4

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 5

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;