How to replace only the first occurrence of a string in PHP
Jul 11, 2025 am 01:09 AM
The first match to replace a string in PHP can be achieved by preg_replace or manually. When using preg_replace, you can control only the first match by setting the fourth parameter to 1. If you replace a normal string, you need to escape with preg_quote; for example, preg_replace('/apple/', 'orange', $string, 1). If you do not use regular expressions, you can manually find the location where the target string first appears, split the string and replace it and splice it. As shown in the function replace_first, use strpos to locate and substr_replace to replace the specified part. Notes include: Use preg_quote to escape when containing special characters. strtr is not suitable for substitution of whole-segment strings. The performance of the two methods is similar, and the choice depends on whether regular functions are required.
Replacing the first match of a string in PHP is not as straightforward as using str_replace , because str_replace will replace all content that appears by default. If you just want to replace the first substring that appears, you need to make a little turn.
Here is a simple and effective method:
Use preg_replace to control the number of replacements
PHP's preg_replace function has a parameter that can control how many replacements can be controlled at most, which is the key to implementing "replace only the first one".
$result = preg_replace('/find content/', 'replaced with content', $subject, 1);
- The first parameter is a regular expression. Note that if you just replace a normal string (no special symbols), you need to use
preg_quote()to escape. - The last parameter
1means that the replacement is at most once, that is, only the first match is replaced.
For example:
$string = "apple banana apple cherry"; $result = preg_replace('/apple/', 'orange', $string, 1); echo $result; // Output: orange banana apple cherry
This only replaces the first "apple".
What if you don't use regularity?
If you don't want to use regular expressions, you can also manually operate the string, and complete it by finding positions and truncating splicing.
The steps are as follows:
- Find the first occurrence of the string to be replaced
- Divide the original string into two parts: the front part and the rear part
- Replace the target string in the first half and then spell the second half.
Code example:
function replace_first($search, $replace, $subject) {
$pos = strpos($subject, $search);
if ($pos === false) return $subject;
return substr_replace($subject, $replace, $pos, strlen($search));
}This method is suitable for scenarios where no regularity is required and is also very efficient.
Notes and FAQs
- If you are sure that
$searchcontains regular special characters, such as.,*,?, etc., remember to escape withpreg_quote($search, '/'). -
str_replacecannot limit the number of replacements, butstrtrcan do single-character replacement and does not apply to the entire string. - In terms of performance, both methods are similar, depending on whether you need regular functions.
Basically that's it. Using preg_replace is the simplest way, while manual processing is more flexible, depending on your specific needs.
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