blocks|key|1267150|text|可以使用preg_replace完成|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1267151|function+str_replace_first($search,+$replace,+$subject)
{
++++$search+=+'/'.preg_quote($search,+'/').'/';
++++return+preg_replace($search,+$replace,+$subject,+1);
}

echo+str_replace_first('abc',+'123',+'abcdef+abcdef+abcdef');+
//+outputs+'123def+abcdef+abcdef'|code-block|syntax|javascript|1267152|神奇之处在于可选的第四个参数限制。从文档中：|1267153|1267154|限制-每个主题字符串中每个模式的最大可能替换数。默认为-1+(无限制)。|blockquote|1267155|1267156|1267157|不过，请参阅zombat's+answer以获得更有效的方法(大致快3-4倍)。|1267158|entityMap|0|LINK|mutability|MUTABLE|url|http://www.php.net/preg_replace|1|https://stackoverflow.com/questions/1252693/using-str-replace-so-that-it-only-acts-on-the-first-match#1252710^0|4|C|0|0|0|0|0|0|0|0|6|F|1|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|D|3|E|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|17|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|18|8|@]|9|@]|C|$]]|$1|L|3|M|5|N|7|19|8|@]|9|@]|C|$]]|$1|O|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]|$1|P|3|-4|5|6|7|1B|8|@]|9|@]|C|$]]|$1|Q|3|R|5|6|7|1C|8|@]|9|@$A|1D|B|1E|1|1F]]|C|$]]|$1|S|3|-4|5|6|7|1G|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]|10|$5|V|W|X|C|$Y|11]]]]

Can be done with <a href="http://www.php.net/preg_replace" rel="noreferrer">preg_replace</a>:
<pre><code>function str_replace_first($search, $replace, $subject)
{
 $search = '/'.preg_quote($search, '/').'/';
 return preg_replace($search, $replace, $subject, 1);
}

echo str_replace_first('abc', '123', 'abcdef abcdef abcdef'); 
// outputs '123def abcdef abcdef'
</code></pre>
The magic is in the optional fourth parameter [Limit]. From the documentation:
<blockquote>
[Limit] - The maximum possible
replacements for each pattern in each
subject string. Defaults to -1 (no
limit).
</blockquote>
 Though, see <a href="https://stackoverflow.com/questions/1252693/using-str-replace-so-that-it-only-acts-on-the-first-match#1252710">zombat's answer</a> for a more efficient method (roughly, 3-4x faster).

blocks|key|1267202|text|最简单的方法是使用正则表达式。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1267203|另一种方法是使用strpos()查找字符串的位置，然后使用substr_replace()|1267204|但我真的会选择RegExp。|1267205|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

The easiest way would be to use regular expression.

The other way is to find the position of the string with strpos() and then an substr_replace()

But i would really go for the RegExp.

blocks|key|1267254|text|它没有版本，但解决方案一点也不老套。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1267255|$pos+=+strpos($haystack,+$needle);
if+($pos+!==+false)+{
++++$newstring+=+substr_replace($haystack,+$replace,+$pos,+strlen($needle));
}|code-block|syntax|javascript|1267256|非常简单，并且节省了正则表达式的性能损失。|1267257|额外的好处:如果你想替换上次出现的代码，只需用strrpos代替strpos即可。|offset|length|style|CODE|1267258|entityMap^0|0|0|0|N|7|W|6|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|T|8|@$K|U|L|V|M|N]|$K|W|L|X|M|N]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

There's no version of it, but the solution isn't hacky at all.

<pre><code>$pos = strpos($haystack, $needle);
if ($pos !== false) {
 $newstring = substr_replace($haystack, $replace, $pos, strlen($needle));
}
</code></pre>

Pretty easy, and saves the performance penalty of regular expressions.

 Bonus: If you want to replace last occurrence, just use <code>strrpos</code> in place of <code>strpos</code>.

blocks|key|1267308|text|不幸的是，我不知道有任何PHP函数可以做到这一点。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1267309|您可以很容易地使用自己的代码，如下所示：|1267310|function+replace_first($find,+$replace,+$subject)+{
++++//+stolen+from+the+comments+at+PHP.net/str_replace
++++//+Splits+$subject+into+an+array+of+2+items+by+$find,
++++//+and+then+joins+the+array+with+$replace
++++return+implode($replace,+explode($find,+$subject,+2));
}|code-block|syntax|javascript|1267311|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Unfortunately, I don't know of any PHP function which can do this. 
You can roll your own fairly easily like this:

<pre><code>function replace_first($find, $replace, $subject) {
 // stolen from the comments at PHP.net/str_replace
 // Splits $subject into an array of 2 items by $find,
 // and then joins the array with $replace
 return implode($replace, explode($find, $subject, 2));
}
</code></pre>

blocks|key|1267360|text|编辑:两个答案都已更新，现在都是正确的。我将留下答案，因为函数计时仍然有用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1267361|不幸的是，'zombat‘和'too+much+php’的答案是错误的。这是对zombat发布的答案的修改(因为我没有足够的名气来发表评论)：|1267362|$pos+=+strpos($haystack,$needle);
if+($pos+!==+false)+{
++++$newstring+=+substr_replace($haystack,$replace,$pos,strlen($needle));
}|code-block|syntax|javascript|1267363|注意strlen($needle)，而不是strlen($replace)。Zombat的例子只有在针和替换的长度相同的情况下才能正常工作。|1267364|下面是一个函数中的相同功能，其签名与PHP自己的str_replace相同：|1267365|function+str_replace_first($search,+$replace,+$subject)+{
++++$pos+=+strpos($subject,+$search);
++++if+($pos+!==+false)+{
++++++++return+substr_replace($subject,+$replace,+$pos,+strlen($search));
++++}
++++return+$subject;
}|1267366|这是修改后的答案“php太多”：|1267367|implode($replace,+explode($search,+$subject,+2));|1267368|请注意末尾的2而不是1。或函数格式：|1267369|function+str_replace_first($search,+$replace,+$subject)+{
++++return+implode($replace,+explode($search,+$subject,+2));
}|1267370|我对这两个函数进行了计时，当找不到匹配项时，第一个函数的速度要快一倍。当找到匹配项时，它们的速度相同。|1267371|entityMap^0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|15|8|@]|9|@]|A|$G|H]]|$1|O|3|P|5|6|7|16|8|@]|9|@]|A|$]]|$1|Q|3|R|5|F|7|17|8|@]|9|@]|A|$G|H]]|$1|S|3|T|5|6|7|18|8|@]|9|@]|A|$]]|$1|U|3|V|5|F|7|19|8|@]|9|@]|A|$G|H]]|$1|W|3|X|5|6|7|1A|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|Z|$]]

Edit: both answers have been updated and are now correct. I'll leave the answer since the function timings are still useful.

The answers by 'zombat' and 'too much php' are unfortunately not correct. This is a revision to the answer zombat posted (as I don't have enough reputation to post a comment):

<pre><code>$pos = strpos($haystack,$needle);
if ($pos !== false) {
 $newstring = substr_replace($haystack,$replace,$pos,strlen($needle));
}
</code></pre>

Note the strlen($needle), instead of strlen($replace). Zombat's example will only work correctly if needle and replace are the same length. 

Here's the same functionality in a function with the same signature as PHP's own str_replace:

<pre><code>function str_replace_first($search, $replace, $subject) {
 $pos = strpos($subject, $search);
 if ($pos !== false) {
 return substr_replace($subject, $replace, $pos, strlen($search));
 }
 return $subject;
}
</code></pre>

This is the revised answer of 'too much php':

<pre><code>implode($replace, explode($search, $subject, 2));
</code></pre>

Note the 2 at the end instead of 1. Or in function format:

<pre><code>function str_replace_first($search, $replace, $subject) {
 return implode($replace, explode($search, $subject, 2));
}
</code></pre>

I timed the two functions and the first one is twice as fast when no match is found. They are the same speed when a match is found.

blocks|key|4483911|text|我创建了这个小函数，用limit替换字符串(区分大小写)上的字符串，而不需要Regexp。它工作得很好。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4483912|function+str_replace_limit($search,+$replace,+$string,+$limit+=+1)+{
++++$pos+=+strpos($string,+$search);

++++if+($pos+===+false)+{
++++++++return+$string;
++++}

++++$searchLen+=+strlen($search);

++++for+($i+=+0;+$i+<+$limit;+$i%2B%2B)+{
++++++++$string+=+substr_replace($string,+$replace,+$pos,+$searchLen);

++++++++$pos+=+strpos($string,+$search);

++++++++if+($pos+===+false)+{
++++++++++++break;
++++++++}
++++}

++++return+$string;
}|code-block|syntax|javascript|4483913|示例用法：|4483914|$search++=+'foo';
$replace+=+'bar';
$string++=+'foo+wizard+makes+foo+brew+for+evil+foo+and+jack';
$limit+++=+2;

$replaced+=+str_replace_limit($search,+$replace,+$string,+$limit);

echo+$replaced;
//+bar+wizard+makes+bar+brew+for+evil+foo+and+jack|4483915|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I created this little function that replaces string on string (case-sensitive) with limit, without the need of Regexp. It works fine.

<pre><code>function str_replace_limit($search, $replace, $string, $limit = 1) {
 $pos = strpos($string, $search);

 if ($pos === false) {
 return $string;
 }

 $searchLen = strlen($search);

 for ($i = 0; $i &lt; $limit; $i++) {
 $string = substr_replace($string, $replace, $pos, $searchLen);

 $pos = strpos($string, $search);

 if ($pos === false) {
 break;
 }
 }

 return $string;
}
</code></pre>

Example usage:

<pre><code>$search = 'foo';
$replace = 'bar';
$string = 'foo wizard makes foo brew for evil foo and jack';
$limit = 2;

$replaced = str_replace_limit($search, $replace, $string, $limit);

echo $replaced;
// bar wizard makes bar brew for evil foo and jack
</code></pre>

blocks|key|197082|text|$string+=+'this+is+my+world,+not+my+world';
$find+=+'world';
$replace+=+'farm';
$result+=+preg_replace("/$find/",$replace,$string,1);
echo+$result;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|197083|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>$string = 'this is my world, not my world';
$find = 'world';
$replace = 'farm';
$result = preg_replace("/$find/",$replace,$string,1);
echo $result;
</code></pre>

blocks|key|1497022|text|为了扩展@renocor's+answer，我编写了一个与str_replace()+100%25向后兼容的函数。也就是说，您可以将所有次出现的str_replace()替换为str_replace_limit()，而不会造成任何混乱，即使那些使用$search、$replace和/或$subject的数组也不会造成任何混乱。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1497023|如果你想用($string===strval(intval(strval($string))))代替函数调用，这个函数可以是完全自包含的，但是我建议你不要这样做，因为在处理以字符串形式提供的整数时，valid_integer()是一个非常有用的函数。|1497024|注意：只要有可能，str_replace_limit()就会使用str_replace()，因此所有对str_replace()的调用都可以替换为str_replace_limit()，而不必担心性能会受到影响。|BOLD|1497025|用法|1497026|<?php
$search+=+'a';
$replace+=+'b';
$subject+=+'abcabc';|code-block|syntax|javascript|1497027|$limit+=+-1;+//+No+limit
$new_string+=+str_replace_limit($search,+$replace,+$subject,+$count,+$limit);
echo+$count.'+replacements+--+'.$new_string;|1497028|1497029|+2的替代品--+bbcbbc|blockquote|1497030|1497031|1497032|$limit+=+1;+//+Limit+of+1
$new_string+=+str_replace_limit($search,+$replace,+$subject,+$count,+$limit);
echo+$count.'+replacements+--+'.$new_string;|1497033|1497034|+1的替代品--+bbcabc|1497035|1497036|1497037|$limit+=+10;+//+Limit+of+10
$new_string+=+str_replace_limit($search,+$replace,+$subject,+$count,+$limit);
echo+$count.'+replacements+--+'.$new_string;|1497038|1497039|+2的替代品--+bbcbbc|1497040|1497041|1497042|函数|1497043|<?php

/**
+*+Checks+if+$string+is+a+valid+integer.+Integers+provided+as+strings+(e.g.+'2'+vs+2)
+*+are+also+supported.
+*+@param+mixed+$string
+*+@return+bool+Returns+boolean+TRUE+if+string+is+a+valid+integer,+or+FALSE+if+it+is+not+
+*/
function+valid_integer($string){
++++//+1.+Cast+as+string+(in+case+integer+is+provided)
++++//+1.+Convert+the+string+to+an+integer+and+back+to+a+string
++++//+2.+Check+if+identical+(note:+'identical',+NOT+just+'equal')
++++//+Note:+TRUE,+FALSE,+and+NULL+$string+values+all+return+FALSE
++++$string+=+strval($string);
++++return+($string===strval(intval($string)));
}

/**
+*+Replace+$limit+occurences+of+the+search+string+with+the+replacement+string
+*+@param+mixed+$search+The+value+being+searched+for,+otherwise+known+as+the+needle.+An
+*+array+may+be+used+to+designate+multiple+needles.
+*+@param+mixed+$replace+The+replacement+value+that+replaces+found+search+values.+An
+*+array+may+be+used+to+designate+multiple+replacements.
+*+@param+mixed+$subject+The+string+or+array+being+searched+and+replaced+on,+otherwise
+*+known+as+the+haystack.+If+subject+is+an+array,+then+the+search+and+replace+is
+*+performed+with+every+entry+of+subject,+and+the+return+value+is+an+array+as+well.+
+*+@param+string+$count+If+passed,+this+will+be+set+to+the+number+of+replacements
+*+performed.
+*+@param+int+$limit+The+maximum+possible+replacements+for+each+pattern+in+each+subject
+*+string.+Defaults+to+-1+(no+limit).
+*+@return+string+This+function+returns+a+string+with+the+replaced+values.
+*/
function+str_replace_limit(
++++++++$search,
++++++++$replace,
++++++++$subject,
++++++++&$count,
++++++++$limit+=+-1
++++){

++++//+Set+some+defaults
++++$count+=+0;

++++//+Invalid+$limit+provided.+Throw+a+warning.
++++if(!valid_integer($limit)){
++++++++$backtrace+=+debug_backtrace();
++++++++trigger_error('Invalid+$limit+`'.$limit.'`+provided+to+'.__function__.'()+in+'.
++++++++++++++++'`'.$backtrace[0]['file'].'`+on+line+'.$backtrace[0]['line'].'.+Expecting+an+'.
++++++++++++++++'integer',+E_USER_WARNING);
++++++++return+$subject;
++++}

++++//+Invalid+$limit+provided.+Throw+a+warning.
++++if($limit<-1){
++++++++$backtrace+=+debug_backtrace();
++++++++trigger_error('Invalid+$limit+`'.$limit.'`+provided+to+'.__function__.'()+in+'.
++++++++++++++++'`'.$backtrace[0]['file'].'`+on+line+'.$backtrace[0]['line'].'.+Expecting+-1+or+'.
++++++++++++++++'a+positive+integer',+E_USER_WARNING);
++++++++return+$subject;
++++}

++++//+No+replacements+necessary.+Throw+a+notice+as+this+was+most+likely+not+the+intended
++++//+use.+And,+if+it+was+(e.g.+part+of+a+loop,+setting+$limit+dynamically),+it+can+be
++++//+worked+around+by+simply+checking+to+see+if+$limit===0,+and+if+it+does,+skip+the
++++//+function+call+(and+set+$count+to+0,+if+applicable).
++++if($limit===0){
++++++++$backtrace+=+debug_backtrace();
++++++++trigger_error('Invalid+$limit+`'.$limit.'`+provided+to+'.__function__.'()+in+'.
++++++++++++++++'`'.$backtrace[0]['file'].'`+on+line+'.$backtrace[0]['line'].'.+Expecting+-1+or+'.
++++++++++++++++'a+positive+integer',+E_USER_NOTICE);
++++++++return+$subject;
++++}

++++//+Use+str_replace()+whenever+possible+(for+performance+reasons)
++++if($limit===-1){
++++++++return+str_replace($search,+$replace,+$subject,+$count);
++++}

++++if(is_array($subject)){

++++++++//+Loop+through+$subject+values+and+call+this+function+for+each+one.
++++++++foreach($subject+as+$key+=>+$this_subject){

++++++++++++//+Skip+values+that+are+arrays+(to+match+str_replace()).
++++++++++++if(!is_array($this_subject)){

++++++++++++++++//+Call+this+function+again+for
++++++++++++++++$this_function+=+__FUNCTION__;
++++++++++++++++$subject[$key]+=+$this_function(
++++++++++++++++++++++++$search,
++++++++++++++++++++++++$replace,
++++++++++++++++++++++++$this_subject,
++++++++++++++++++++++++$this_count,
++++++++++++++++++++++++$limit
++++++++++++++++);

++++++++++++++++//+Adjust+$count
++++++++++++++++$count+%2B=+$this_count;

++++++++++++++++//+Adjust+$limit,+if+not+-1
++++++++++++++++if($limit!=-1){
++++++++++++++++++++$limit+-=+$this_count;
++++++++++++++++}

++++++++++++++++//+Reached+$limit,+return+$subject
++++++++++++++++if($limit===0){
++++++++++++++++++++return+$subject;
++++++++++++++++}

++++++++++++}

++++++++}

++++++++return+$subject;

++++}+elseif(is_array($search)){
++++++++//+Only+treat+$replace+as+an+array+if+$search+is+also+an+array+(to+match+str_replace())

++++++++//+Clear+keys+of+$search+(to+match+str_replace()).
++++++++$search+=+array_values($search);

++++++++//+Clear+keys+of+$replace,+if+applicable+(to+match+str_replace()).
++++++++if(is_array($replace)){
++++++++++++$replace+=+array_values($replace);
++++++++}

++++++++//+Loop+through+$search+array.
++++++++foreach($search+as+$key+=>+$this_search){

++++++++++++//+Don't+support+multi-dimensional+arrays+(to+match+str_replace()).
++++++++++++$this_search+=+strval($this_search);

++++++++++++//+If+$replace+is+an+array,+use+the+value+of+$replace[$key]+as+the+replacement.+If
++++++++++++//+$replace[$key]+doesn't+exist,+just+an+empty+string+(to+match+str_replace()).
++++++++++++if(is_array($replace)){
++++++++++++++++if(array_key_exists($key,+$replace)){
++++++++++++++++++++$this_replace+=+strval($replace[$key]);
++++++++++++++++}+else+{
++++++++++++++++++++$this_replace+=+'';
++++++++++++++++}
++++++++++++}+else+{
++++++++++++++++$this_replace+=+strval($replace);
++++++++++++}

++++++++++++//+Call+this+function+again+for
++++++++++++$this_function+=+__FUNCTION__;
++++++++++++$subject+=+$this_function(
++++++++++++++++++++$this_search,
++++++++++++++++++++$this_replace,
++++++++++++++++++++$subject,
++++++++++++++++++++$this_count,
++++++++++++++++++++$limit
++++++++++++);

++++++++++++//+Adjust+$count
++++++++++++$count+%2B=+$this_count;

++++++++++++//+Adjust+$limit,+if+not+-1
++++++++++++if($limit!=-1){
++++++++++++++++$limit+-=+$this_count;
++++++++++++}

++++++++++++//+Reached+$limit,+return+$subject
++++++++++++if($limit===0){
++++++++++++++++return+$subject;
++++++++++++}

++++++++}

++++++++return+$subject;

++++}+else+{
++++++++$search+=+strval($search);
++++++++$replace+=+strval($replace);

++++++++//+Get+position+of+first+$search
++++++++$pos+=+strpos($subject,+$search);

++++++++//+Return+$subject+if+$search+cannot+be+found
++++++++if($pos===false){
++++++++++++return+$subject;
++++++++}

++++++++//+Get+length+of+$search,+to+make+proper+replacement+later+on
++++++++$search_len+=+strlen($search);

++++++++//+Loop+until+$search+can+no+longer+be+found,+or+$limit+is+reached
++++++++for($i=0;(($i<$limit)%7C%7C($limit===-1));$i%2B%2B){

++++++++++++//+Replace+
++++++++++++$subject+=+substr_replace($subject,+$replace,+$pos,+$search_len);

++++++++++++//+Increase+$count
++++++++++++$count%2B%2B;

++++++++++++//+Get+location+of+next+$search
++++++++++++$pos+=+strpos($subject,+$search);

++++++++++++//+Break+out+of+loop+if+$needle
++++++++++++if($pos===false){
++++++++++++++++break;
++++++++++++}

++++++++}

++++++++//+Return+new+$subject
++++++++return+$subject;

++++}

}|1497044|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/8439478/526741^0|T|D|1Y|D|2E|J|3E|7|3M|8|3X|8|4|H|0|0|5|17|2R|F|0|0|3|9|J|W|D|1F|D|21|J|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1P|8|@$9|1Q|A|1R|B|C]|$9|1S|A|1T|B|C]|$9|1U|A|1V|B|C]|$9|1W|A|1X|B|C]|$9|1Y|A|1Z|B|C]|$9|20|A|21|B|C]]|D|@$9|22|A|23|1|24]]|E|$]]|$1|F|3|G|5|6|7|25|8|@$9|26|A|27|B|C]|$9|28|A|29|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|2A|8|@$9|2B|A|2C|B|J]|$9|2D|A|2E|B|C]|$9|2F|A|2G|B|C]|$9|2H|A|2I|B|C]|$9|2J|A|2K|B|C]]|D|@]|E|$]]|$1|K|3|L|5|6|7|2L|8|@]|D|@]|E|$]]|$1|M|3|N|5|O|7|2M|8|@]|D|@]|E|$P|Q]]|$1|R|3|S|5|O|7|2N|8|@]|D|@]|E|$P|Q]]|$1|T|3|-4|5|6|7|2O|8|@]|D|@]|E|$]]|$1|U|3|V|5|W|7|2P|8|@]|D|@]|E|$]]|$1|X|3|-4|5|6|7|2Q|8|@]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|2R|8|@]|D|@]|E|$]]|$1|Z|3|10|5|O|7|2S|8|@]|D|@]|E|$P|Q]]|$1|11|3|-4|5|6|7|2T|8|@]|D|@]|E|$]]|$1|12|3|13|5|W|7|2U|8|@]|D|@]|E|$]]|$1|14|3|-4|5|6|7|2V|8|@]|D|@]|E|$]]|$1|15|3|-4|5|6|7|2W|8|@]|D|@]|E|$]]|$1|16|3|17|5|O|7|2X|8|@]|D|@]|E|$P|Q]]|$1|18|3|-4|5|6|7|2Y|8|@]|D|@]|E|$]]|$1|19|3|1A|5|W|7|2Z|8|@]|D|@]|E|$]]|$1|1B|3|-4|5|6|7|30|8|@]|D|@]|E|$]]|$1|1C|3|-4|5|6|7|31|8|@]|D|@]|E|$]]|$1|1D|3|1E|5|6|7|32|8|@]|D|@]|E|$]]|$1|1F|3|1G|5|O|7|33|8|@]|D|@]|E|$P|Q]]|$1|1H|3|-4|5|6|7|34|8|@]|D|@]|E|$]]]|1I|$1J|$5|1K|1L|1M|E|$1N|1O]]]]

To expand on <a href="https://stackoverflow.com/a/8439478/526741">@renocor's answer</a>, I've written a function that is 100% backward-compatible with <code>str_replace()</code>. That is, you can replace all occurrences of <code>str_replace()</code> with <code>str_replace_limit()</code> without messing anything up, even those using arrays for the <code>$search</code>, <code>$replace</code>, and/or <code>$subject</code>.

The function could be completely self-contained, if you wanted to replace the function call with <code>($string===strval(intval(strval($string))))</code>, but I'd recommend against it since <code>valid_integer()</code> is a rather useful function when dealing with integers provided as strings.

Note: Whenever possible, <code>str_replace_limit()</code> will use <code>str_replace()</code> instead, so all calls to <code>str_replace()</code> can be replaced with <code>str_replace_limit()</code> without worrying about a hit to performance.

<h1>Usage</h1>

<pre><code>&lt;?php
$search = 'a';
$replace = 'b';
$subject = 'abcabc';
</code></pre>



<pre><code>$limit = -1; // No limit
$new_string = str_replace_limit($search, $replace, $subject, $count, $limit);
echo $count.' replacements -- '.$new_string;
</code></pre>

<blockquote>
 2 replacements -- bbcbbc
</blockquote>

<pre><code>$limit = 1; // Limit of 1
$new_string = str_replace_limit($search, $replace, $subject, $count, $limit);
echo $count.' replacements -- '.$new_string;
</code></pre>

<blockquote>
 1 replacements -- bbcabc
</blockquote>

<pre><code>$limit = 10; // Limit of 10
$new_string = str_replace_limit($search, $replace, $subject, $count, $limit);
echo $count.' replacements -- '.$new_string;
</code></pre>

<blockquote>
 2 replacements -- bbcbbc
</blockquote>

<h1>Function</h1>

<pre><code>&lt;?php

/**
 * Checks if $string is a valid integer. Integers provided as strings (e.g. '2' vs 2)
 * are also supported.
 * @param mixed $string
 * @return bool Returns boolean TRUE if string is a valid integer, or FALSE if it is not 
 */
function valid_integer($string){
 // 1. Cast as string (in case integer is provided)
 // 1. Convert the string to an integer and back to a string
 // 2. Check if identical (note: 'identical', NOT just 'equal')
 // Note: TRUE, FALSE, and NULL $string values all return FALSE
 $string = strval($string);
 return ($string===strval(intval($string)));
}

/**
 * Replace $limit occurences of the search string with the replacement string
 * @param mixed $search The value being searched for, otherwise known as the needle. An
 * array may be used to designate multiple needles.
 * @param mixed $replace The replacement value that replaces found search values. An
 * array may be used to designate multiple replacements.
 * @param mixed $subject The string or array being searched and replaced on, otherwise
 * known as the haystack. If subject is an array, then the search and replace is
 * performed with every entry of subject, and the return value is an array as well. 
 * @param string $count If passed, this will be set to the number of replacements
 * performed.
 * @param int $limit The maximum possible replacements for each pattern in each subject
 * string. Defaults to -1 (no limit).
 * @return string This function returns a string with the replaced values.
 */
function str_replace_limit(
 $search,
 $replace,
 $subject,
 &amp;$count,
 $limit = -1
 ){

 // Set some defaults
 $count = 0;

 // Invalid $limit provided. Throw a warning.
 if(!valid_integer($limit)){
 $backtrace = debug_backtrace();
 trigger_error('Invalid $limit `'.$limit.'` provided to '.__function__.'() in '.
 '`'.$backtrace[0]['file'].'` on line '.$backtrace[0]['line'].'. Expecting an '.
 'integer', E_USER_WARNING);
 return $subject;
 }

 // Invalid $limit provided. Throw a warning.
 if($limit&lt;-1){
 $backtrace = debug_backtrace();
 trigger_error('Invalid $limit `'.$limit.'` provided to '.__function__.'() in '.
 '`'.$backtrace[0]['file'].'` on line '.$backtrace[0]['line'].'. Expecting -1 or '.
 'a positive integer', E_USER_WARNING);
 return $subject;
 }

 // No replacements necessary. Throw a notice as this was most likely not the intended
 // use. And, if it was (e.g. part of a loop, setting $limit dynamically), it can be
 // worked around by simply checking to see if $limit===0, and if it does, skip the
 // function call (and set $count to 0, if applicable).
 if($limit===0){
 $backtrace = debug_backtrace();
 trigger_error('Invalid $limit `'.$limit.'` provided to '.__function__.'() in '.
 '`'.$backtrace[0]['file'].'` on line '.$backtrace[0]['line'].'. Expecting -1 or '.
 'a positive integer', E_USER_NOTICE);
 return $subject;
 }

 // Use str_replace() whenever possible (for performance reasons)
 if($limit===-1){
 return str_replace($search, $replace, $subject, $count);
 }

 if(is_array($subject)){

 // Loop through $subject values and call this function for each one.
 foreach($subject as $key =&gt; $this_subject){

 // Skip values that are arrays (to match str_replace()).
 if(!is_array($this_subject)){

 // Call this function again for
 $this_function = __FUNCTION__;
 $subject[$key] = $this_function(
 $search,
 $replace,
 $this_subject,
 $this_count,
 $limit
 );

 // Adjust $count
 $count += $this_count;

 // Adjust $limit, if not -1
 if($limit!=-1){
 $limit -= $this_count;
 }

 // Reached $limit, return $subject
 if($limit===0){
 return $subject;
 }

 }

 }

 return $subject;

 } elseif(is_array($search)){
 // Only treat $replace as an array if $search is also an array (to match str_replace())

 // Clear keys of $search (to match str_replace()).
 $search = array_values($search);

 // Clear keys of $replace, if applicable (to match str_replace()).
 if(is_array($replace)){
 $replace = array_values($replace);
 }

 // Loop through $search array.
 foreach($search as $key =&gt; $this_search){

 // Don't support multi-dimensional arrays (to match str_replace()).
 $this_search = strval($this_search);

 // If $replace is an array, use the value of $replace[$key] as the replacement. If
 // $replace[$key] doesn't exist, just an empty string (to match str_replace()).
 if(is_array($replace)){
 if(array_key_exists($key, $replace)){
 $this_replace = strval($replace[$key]);
 } else {
 $this_replace = '';
 }
 } else {
 $this_replace = strval($replace);
 }

 // Call this function again for
 $this_function = __FUNCTION__;
 $subject = $this_function(
 $this_search,
 $this_replace,
 $subject,
 $this_count,
 $limit
 );

 // Adjust $count
 $count += $this_count;

 // Adjust $limit, if not -1
 if($limit!=-1){
 $limit -= $this_count;
 }

 // Reached $limit, return $subject
 if($limit===0){
 return $subject;
 }

 }

 return $subject;

 } else {
 $search = strval($search);
 $replace = strval($replace);

 // Get position of first $search
 $pos = strpos($subject, $search);

 // Return $subject if $search cannot be found
 if($pos===false){
 return $subject;
 }

 // Get length of $search, to make proper replacement later on
 $search_len = strlen($search);

 // Loop until $search can no longer be found, or $limit is reached
 for($i=0;(($i&lt;$limit)||($limit===-1));$i++){

 // Replace 
 $subject = substr_replace($subject, $replace, $pos, $search_len);

 // Increase $count
 $count++;

 // Get location of next $search
 $pos = strpos($subject, $search);

 // Break out of loop if $needle
 if($pos===false){
 break;
 }

 }

 // Return new $subject
 return $subject;

 }

}
</code></pre>

blocks|key|197389|text|您可以使用以下命令：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|197390|function+str_replace_once($str_pattern,+$str_replacement,+$string){+

++++++++if+(strpos($string,+$str_pattern)+!==+false){+
++++++++++++$occurrence+=+strpos($string,+$str_pattern);+
++++++++++++return+substr_replace($string,+$str_replacement,+strpos($string,+$str_pattern),+strlen($str_pattern));+
++++++++}+

++++++++return+$string;+
++++}+|code-block|syntax|javascript|197391|我从php.net找到了这个例子|197392|用法：|197393|$string+=+"Thiz+iz+an+examplz";
var_dump(str_replace_once('z','Z',+$string));+|197394|输出：|197395|ThiZ+iz+an+examplz|197396|这可能会稍微降低性能，但这是最简单的解决方案。|197397|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

You can use this:

<pre><code>function str_replace_once($str_pattern, $str_replacement, $string){ 

 if (strpos($string, $str_pattern) !== false){ 
 $occurrence = strpos($string, $str_pattern); 
 return substr_replace($string, $str_replacement, strpos($string, $str_pattern), strlen($str_pattern)); 
 } 

 return $string; 
 } 
</code></pre>

Found this example from php.net

Usage:

<pre><code>$string = "Thiz iz an examplz";
var_dump(str_replace_once('z','Z', $string)); 
</code></pre>

Output:

<pre><code>ThiZ iz an examplz
</code></pre>

This may reduce the performance a little bit, but the easiest solution.

blocks|key|1267596|text|根据我的测试结果，我想投票给karim79提供的regular_express+one。(我现在没有足够的名气来投票！)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1267597|来自zombat的解决方案使用了太多的函数调用，我甚至简化了代码。我使用PHP5.4对这两个解决方案运行了100,000次，结果如下：|1267598|$str+=+'Hello+abc,+have+a+nice+day+abc!+abc!';
$pos+=+strpos($str,+'abc');
$str+=+substr_replace($str,+'123',+$pos,+3);|code-block|syntax|javascript|1267599|==>+1.85秒|1267600|$str+=+'Hello+abc,+have+a+nice+day+abc!+abc!';
$str+=+preg_replace('/abc/',+'123',+$str,+1);|1267601|==>+1.35秒|1267602|如你所见。preg_replace的性能并不像许多人认为的那么差。因此，如果您的常规表达式不复杂，我建议您使用经典的解决方案。|1267603|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

According to my test result, I'd like to vote the regular_express one provided by karim79. (I don't have enough reputation to vote it now!)

The solution from zombat uses too many function calls, I even simplify the codes. I'm using PHP 5.4 to run both solutions for 100,000 times, and here's the result:

<pre><code>$str = 'Hello abc, have a nice day abc! abc!';
$pos = strpos($str, 'abc');
$str = substr_replace($str, '123', $pos, 3);
</code></pre>

==> 1.85 sec

<pre><code>$str = 'Hello abc, have a nice day abc! abc!';
$str = preg_replace('/abc/', '123', $str, 1);
</code></pre>

==> 1.35 sec

As you can see. The performance of preg_replace is not so bad as many people think. So I'd suggest the classy solution if your regular express is not complicated.

blocks|key|197181|text|为了扩展zombat的答案(我认为这是最好的答案)，我创建了他的函数的递归版本，该函数接受一个$limit参数来指定要替换的匹配项的数量。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|197182|function+str_replace_limit($haystack,+$needle,+$replace,+$limit,+$start_pos+=+0)+{
++++if+($limit+<=+0)+{
++++++++return+$haystack;
++++}+else+{
++++++++$pos+=+strpos($haystack,$needle,$start_pos);
++++++++if+($pos+!==+false)+{
++++++++++++$newstring+=+substr_replace($haystack,+$replace,+$pos,+strlen($needle));
++++++++++++return+str_replace_limit($newstring,+$needle,+$replace,+$limit-1,+$pos%2Bstrlen($replace));
++++++++}+else+{
++++++++++++return+$haystack;
++++++++}
++++}
}|code-block|syntax|javascript|197183|entityMap^0|1B|6|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

To expand on zombat's answer (which I believe to be the best answer), I created a recursive version of his function that takes in a <code>$limit</code> parameter to specify how many occurrences you want to replace.

<pre><code>function str_replace_limit($haystack, $needle, $replace, $limit, $start_pos = 0) {
 if ($limit &lt;= 0) {
 return $haystack;
 } else {
 $pos = strpos($haystack,$needle,$start_pos);
 if ($pos !== false) {
 $newstring = substr_replace($haystack, $replace, $pos, strlen($needle));
 return str_replace_limit($newstring, $needle, $replace, $limit-1, $pos+strlen($replace));
 } else {
 return $haystack;
 }
 }
}
</code></pre>

blocks|key|1498870|text|对于字符串|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1498871|$string+=+'OOO.OOO.OOO.S';
$search+=+'OOO';
$replace+=+'B';

//replace+ONLY+FIRST+occurance+of+"OOO"+with+"B"
++++$string+=+substr_replace($string,$replace,0,strlen($search));
++++//$string+=>+B.OOO.OOO.S

//replace+ONLY+LAST+occurance+of+"OOOO"+with+"B"
++++$string+=+substr_replace($string,$replace,strrpos($string,$search),strlen($search))+
++++//$string+=>+OOO.OOO.B.S

++++//replace+ONLY+LAST+occurance+of+"OOOO"+with+"B"
++++$string+=+strrev(implode(strrev($replace),explode(strrev($search),strrev($string),2)))
++++//$string+=>+OOO.OOO.B.S|code-block|syntax|javascript|1498872|对于单个字符|1498873|$string[strpos($string,$search)]+=+$replace;


//EXAMPLE

$string+=+'O.O.O.O.S';
$search+=+'O';
$replace+=+'B';

//replace+ONLY+FIRST+occurance+of+"O"+with+"B"+
++++$string[strpos($string,$search)]+=+$replace;++
++++//$string+=>+B.O.O.O.S

//replace+ONLY+LAST+occurance+of+"O"+with+"B"+
++++$string[strrpos($string,$search)]+=+$replace;+
++++//+$string+=>+B.O.O.B.S|1498874|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

For a string

<pre><code>$string = 'OOO.OOO.OOO.S';
$search = 'OOO';
$replace = 'B';

//replace ONLY FIRST occurance of "OOO" with "B"
 $string = substr_replace($string,$replace,0,strlen($search));
 //$string =&gt; B.OOO.OOO.S

//replace ONLY LAST occurance of "OOOO" with "B"
 $string = substr_replace($string,$replace,strrpos($string,$search),strlen($search)) 
 //$string =&gt; OOO.OOO.B.S

 //replace ONLY LAST occurance of "OOOO" with "B"
 $string = strrev(implode(strrev($replace),explode(strrev($search),strrev($string),2)))
 //$string =&gt; OOO.OOO.B.S
</code></pre>

For a single character

<pre><code>$string[strpos($string,$search)] = $replace;


//EXAMPLE

$string = 'O.O.O.O.S';
$search = 'O';
$replace = 'B';

//replace ONLY FIRST occurance of "O" with "B" 
 $string[strpos($string,$search)] = $replace; 
 //$string =&gt; B.O.O.O.S

//replace ONLY LAST occurance of "O" with "B" 
 $string[strrpos($string,$search)] = $replace; 
 // $string =&gt; B.O.O.B.S
</code></pre>

blocks|key|1267785|text|我想知道哪一个是最快的，所以我都测试了一下。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1267786|你会在下面找到：|1267787|1267788|此页面上提供的所有函数的综合列表|unordered-list-item|1267789|Benchmark测试每个结构(平均执行时间超过10,000次)|1267790|链接到每个答案(完整代码)|1267791|1267792|1267793|所有功能都使用相同的设置进行测试：|1267794|$string+=+'OOO.OOO.OOO.S';
$search+=+'OOO';+
$replace+=+'B';|code-block|syntax|javascript|1267795|1267796|仅在字符串中出现第一个时替换的函数：|offset|length|style|BOLD|1267797|1267798|substr_replace($string,+$replace,+0,+strlen($search));|CODE|1267799|1267800|由=>+FASTEST|1267801|replace_first($search,+$replace,+$string);贡献：=>+zombat+OOO.S+=>+B.OOO.OOO.S+AVERAGE+TIME+=>+0.0000062883+SLOWER+BY+=>zombat|1267802|1267803|由=>+too+TIME+php+OOO.S+=>+B.OOO.OOO.S+AVERAGE+TIME+=>+0.0000073902+SLOWER+BY+=>+OOO.S贡献|1267804|由=>+karim79+OOO.S+=>+B.OOO.OOO.S+AVERAGE+TIME+=>+0.0000077519+SLOWER由=>+23.27%25|1267805|str_replace_once($search,+$replace,+$string);贡献|1267806|1267807|由=>+happyhardik+OOO.S+=>+B.OOO.OOO.S+AVERAGE+TIME+=>+0.0000082286+SLOWER+BY+=>+happyhardik+OOO.S贡献|1267808|由=>+32.54%25|1267809|str_replace_limit($search,+$replace,+$string,+1);贡献-扩展的renocor+OOO.S+=>+B.OOO.S平均时间=>慢0.0000083342由=>+bfrohs提供|1267810|1267811|由=>+renocor贡献OOO.S+=>+B.OOO.OO.s+AVERAGE+TIME+=>+0.0000093116+SLOWER+BY+=>+renocor|1267812|由=>+jayoaK+OOO.S+=>+B.OOO.S贡献平均时间=>比=>慢0.0000093862+49.26%25|1267813|1267814|仅替换字符串中最后出现的字符串的的函数：|1267815|1267816|substr_replace($string,+$replace,+strrpos($string,+$search),+strlen($search));|1267817|1267818|由=>+oLinkSoftware提供-+modified+zombat+OOO.S+=>+OOO.OO.B.s+AVERAGE+TIME+=>+0.0000068083+SLOWER+BY+=>+zombat|1267819|由=>+oLinkSoftware+OOO.S+=>+OOO.OOO.B.S平均时间=>慢0.0000084460+=>+24.05%25贡献|1267820|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/1252710/1159603|1|https://stackoverflow.com/a/1252717/1159603|2|https://stackoverflow.com/a/14710201/1159603|3|https://stackoverflow.com/a/8439478/1159603|4|https://stackoverflow.com/a/22269776/1159603^0|0|0|0|0|0|0|0|0|0|0|0|E|4|0|0|0|1I|0|1I|0|1I|0|0|0|0|B|0|0|3F|0|16|0|16|1|0|0|0|2F|0|0|26|0|0|1B|0|19|0|19|2|0|0|0|2Q|0|0|A|0|0|32|0|1D|0|1D|3|0|0|0|2A|0|0|1M|0|0|0|K|0|0|0|26|0|26|0|26|4|0|0|0|2X|0|0|1X|0^^$0|@$1|2|3|4|5|6|7|2K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|2L|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|2M|8|@]|9|@]|A|$]]|$1|E|3|F|5|G|7|2N|8|@]|9|@]|A|$]]|$1|H|3|I|5|G|7|2O|8|@]|9|@]|A|$]]|$1|J|3|K|5|G|7|2P|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|2Q|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|2R|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|2S|8|@]|9|@]|A|$]]|$1|P|3|Q|5|R|7|2T|8|@]|9|@]|A|$S|T]]|$1|U|3|-4|5|6|7|2U|8|@]|9|@]|A|$]]|$1|V|3|W|5|6|7|2V|8|@$X|2W|Y|2X|Z|10]]|9|@]|A|$]]|$1|11|3|-4|5|6|7|2Y|8|@]|9|@]|A|$]]|$1|12|3|13|5|G|7|2Z|8|@$X|30|Y|31|Z|10]|$X|32|Y|33|Z|14]]|9|@$X|34|Y|35|1|36]]|A|$]]|$1|15|3|-4|5|6|7|37|8|@]|9|@]|A|$]]|$1|16|3|17|5|6|7|38|8|@$X|39|Y|3A|Z|10]]|9|@]|A|$]]|$1|18|3|19|5|G|7|3B|8|@$X|3C|Y|3D|Z|10]|$X|3E|Y|3F|Z|14]]|9|@$X|3G|Y|3H|1|3I]]|A|$]]|$1|1A|3|-4|5|6|7|3J|8|@]|9|@]|A|$]]|$1|1B|3|1C|5|6|7|3K|8|@$X|3L|Y|3M|Z|10]]|9|@]|A|$]]|$1|1D|3|1E|5|6|7|3N|8|@$X|3O|Y|3P|Z|10]]|9|@]|A|$]]|$1|1F|3|1G|5|G|7|3Q|8|@$X|3R|Y|3S|Z|10]|$X|3T|Y|3U|Z|14]]|9|@$X|3V|Y|3W|1|3X]]|A|$]]|$1|1H|3|-4|5|6|7|3Y|8|@]|9|@]|A|$]]|$1|1I|3|1J|5|6|7|3Z|8|@$X|40|Y|41|Z|10]]|9|@]|A|$]]|$1|1K|3|1L|5|6|7|42|8|@$X|43|Y|44|Z|10]]|9|@]|A|$]]|$1|1M|3|1N|5|G|7|45|8|@$X|46|Y|47|Z|10]|$X|48|Y|49|Z|14]]|9|@$X|4A|Y|4B|1|4C]]|A|$]]|$1|1O|3|-4|5|6|7|4D|8|@]|9|@]|A|$]]|$1|1P|3|1Q|5|6|7|4E|8|@$X|4F|Y|4G|Z|10]]|9|@]|A|$]]|$1|1R|3|1S|5|6|7|4H|8|@$X|4I|Y|4J|Z|10]]|9|@]|A|$]]|$1|1T|3|-4|5|6|7|4K|8|@]|9|@]|A|$]]|$1|1U|3|1V|5|6|7|4L|8|@$X|4M|Y|4N|Z|10]]|9|@]|A|$]]|$1|1W|3|-4|5|6|7|4O|8|@]|9|@]|A|$]]|$1|1X|3|1Y|5|G|7|4P|8|@$X|4Q|Y|4R|Z|10]|$X|4S|Y|4T|Z|14]]|9|@$X|4U|Y|4V|1|4W]]|A|$]]|$1|1Z|3|-4|5|6|7|4X|8|@]|9|@]|A|$]]|$1|20|3|21|5|6|7|4Y|8|@$X|4Z|Y|50|Z|10]]|9|@]|A|$]]|$1|22|3|23|5|6|7|51|8|@$X|52|Y|53|Z|10]]|9|@]|A|$]]|$1|24|3|-4|5|6|7|54|8|@]|9|@]|A|$]]]|25|$26|$5|27|28|29|A|$2A|2B]]|2C|$5|27|28|29|A|$2A|2D]]|2E|$5|27|28|29|A|$2A|2F]]|2G|$5|27|28|29|A|$2A|2H]]|2I|$5|27|28|29|A|$2A|2J]]]]

I wondered which one was the fastest, so I tested them all.

Below you will find:

<ul>
<li>A comprehensive list of all the functions that have been contributed onto this page</li>
<li>Benchmark testing for each contrubution (average execution time over 10,000 runs)</li>
<li>Links to each answer (for the full code)</li>
</ul>

<hr>

All functions were tested with the same settings:

<pre><code>$string = 'OOO.OOO.OOO.S';
$search = 'OOO'; 
$replace = 'B';
</code></pre>

<hr>

Functions that only replace the first occurrence of a string within a string:

<ul>
<li><a href="https://stackoverflow.com/a/1252710/1159603"><code>substr_replace($string, $replace, 0, strlen($search));</code></a>

<pre><code>[CONTRIBUTED BY] =&gt; zombat
[OOO.OOO.OOO.S] =&gt; B.OOO.OOO.S
[AVERAGE TIME] =&gt; 0.0000062883
[SLOWER BY] =&gt; FASTEST
</code></pre></li>
<li><a href="https://stackoverflow.com/a/1252717/1159603"><code>replace_first($search, $replace, $string);</code></a>

<pre><code>[CONTRIBUTED BY] =&gt; too much php
[OOO.OOO.OOO.S] =&gt; B.OOO.OOO.S
[AVERAGE TIME] =&gt; 0.0000073902
[SLOWER BY] =&gt; 17.52%
</code></pre></li>
<li><a href="https://stackoverflow.com/a/1252705/1159603"><code>preg_replace($search, $replace, $string, 1);</code></a>

<pre><code>[CONTRIBUTED BY] =&gt; karim79
[OOO.OOO.OOO.S] =&gt; B.OOO.OOO.S
[AVERAGE TIME] =&gt; 0.0000077519
[SLOWER BY] =&gt; 23.27%
</code></pre></li>
<li><a href="https://stackoverflow.com/a/14710201/1159603"><code>str_replace_once($search, $replace, $string);</code></a>

<pre><code>[CONTRIBUTED BY] =&gt; happyhardik
[OOO.OOO.OOO.S] =&gt; B.OOO.OOO.S
[AVERAGE TIME] =&gt; 0.0000082286
[SLOWER BY] =&gt; 30.86%
</code></pre></li>
<li><a href="https://stackoverflow.com/a/11400172/1159603"><code>str_replace_limit($search, $replace, $string, $count, 1);</code></a>

<pre><code>[CONTRIBUTED BY] =&gt; bfrohs - expanded renocor
[OOO.OOO.OOO.S] =&gt; B.OOO.OOO.S
[AVERAGE TIME] =&gt; 0.0000083342
[SLOWER BY] =&gt; 32.54%
</code></pre></li>
<li><a href="https://stackoverflow.com/a/8439478/1159603"><code>str_replace_limit($search, $replace, $string, 1);</code></a>

<pre><code>[CONTRIBUTED BY] =&gt; renocor
[OOO.OOO.OOO.S] =&gt; B.OOO.OOO.S
[AVERAGE TIME] =&gt; 0.0000093116
[SLOWER BY] =&gt; 48.08%
</code></pre></li>
<li><a href="https://stackoverflow.com/a/21066690/1159603"><code>str_replace_limit($string, $search, $replace, 1, 0);</code></a>

<pre><code>[CONTRIBUTED BY] =&gt; jayoaK
[OOO.OOO.OOO.S] =&gt; B.OOO.OOO.S
[AVERAGE TIME] =&gt; 0.0000093862
[SLOWER BY] =&gt; 49.26%
</code></pre></li>
</ul>

<hr>

Functions that only replace the last occurrence of a string within a string:

<ul>
<li><a href="https://stackoverflow.com/a/22269776/1159603"><code>substr_replace($string, $replace, strrpos($string, $search), strlen($search));</code></a>

<pre><code>[CONTRIBUTED BY] =&gt; oLinkSoftware - modified zombat
[OOO.OOO.OOO.S] =&gt; OOO.OOO.B.S
[AVERAGE TIME] =&gt; 0.0000068083
[SLOWER BY] =&gt; FASTEST
</code></pre></li>
<li><a href="https://stackoverflow.com/a/22269776/1159603"><code>strrev(implode(strrev($replace), explode(strrev($search), strrev($string), 2)));</code></a>

<pre><code>[CONTRIBUTED BY] =&gt; oLinkSoftware
[OOO.OOO.OOO.S] =&gt; OOO.OOO.B.S
[AVERAGE TIME] =&gt; 0.0000084460
[SLOWER BY] =&gt; 24.05%
</code></pre></li>
</ul>

blocks|key|1498967|text|下面是我创建的一个简单类，用于包装略微修改过的str_replace()函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1498968|我们的php::str_rreplace()函数还允许您执行一个反向的、有限的str_replace()，这在尝试仅替换字符串的最后一个X实例时非常方便。|1498969|这两个示例都使用preg_replace()。|1498970|<?php
class+php+{

++++/**
++++*+str_replace()+from+the+end+of+a+string+that+can+also+be+limited+e.g.+replace+only+the+last+instance+of+'</div>'+with+''
++++*
++++*+@param+string+++$find
++++*+@param+string+++$replace
++++*+@param+string+++$subject
++++*+@param+int++++++$replacement_limit+%7C+-1+to+replace+all+references
++++*
++++*+@return+string
++++*/
++++public+static+function+str_replace($find,+$replace,+$subject,+$replacement_limit+=+-1)+{
++++++++$find_pattern+=+str_replace('/',+'\/',+$find);
++++++++return+preg_replace('/'+.+$find_pattern+.+'/',+$replace,+$subject,+$replacement_limit);
++++}

++++/**
++++*+str_replace()+from+the+end+of+a+string+that+can+also+be+limited+e.g.+replace+only+the+last+instance+of+'</div>'+with+''
++++*
++++*+@param+string+++$find
++++*+@param+string+++$replace
++++*+@param+string+++$subject
++++*+@param+int++++++$replacement_limit+%7C+-1+to+replace+all+references
++++*
++++*+@return+string
++++*/
++++public+static+function+str_rreplace($find,+$replace,+$subject,+$replacement_limit+=+-1)+{
++++++++return+strrev(+self::str_replace(strrev($find),+strrev($replace),+strrev($subject),+$replacement_limit)+);
++++}
}|code-block|syntax|javascript|1498971|entityMap|0|LINK|mutability|MUTABLE|url|http://www.php.net/str_replace|1|http://www.php.net/preg_replace^0|N|D|0|0|0|8|E|1|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|H|3|I|5|J|7|15|8|@]|9|@]|C|$K|L]]|$1|M|3|-4|5|6|7|16|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

Here's a simple class I created to wrap our slightly modified <a href="http://www.php.net/str_replace" rel="nofollow">str_replace()</a> functions.

Our php::str_rreplace() function also allows you to carry out a reverse, limited str_replace() which can be very handy when trying to replace only the final X instance(s) of a string.

These examples both use <a href="http://www.php.net/preg_replace" rel="nofollow">preg_replace()</a>.

<pre><code>&lt;?php
class php {

 /**
 * str_replace() from the end of a string that can also be limited e.g. replace only the last instance of '&lt;/div&gt;' with ''
 *
 * @param string $find
 * @param string $replace
 * @param string $subject
 * @param int $replacement_limit | -1 to replace all references
 *
 * @return string
 */
 public static function str_replace($find, $replace, $subject, $replacement_limit = -1) {
 $find_pattern = str_replace('/', '\/', $find);
 return preg_replace('/' . $find_pattern . '/', $replace, $subject, $replacement_limit);
 }

 /**
 * str_replace() from the end of a string that can also be limited e.g. replace only the last instance of '&lt;/div&gt;' with ''
 *
 * @param string $find
 * @param string $replace
 * @param string $subject
 * @param int $replacement_limit | -1 to replace all references
 *
 * @return string
 */
 public static function str_rreplace($find, $replace, $subject, $replacement_limit = -1) {
 return strrev( self::str_replace(strrev($find), strrev($replace), strrev($subject), $replacement_limit) );
 }
}
</code></pre>

blocks|key|1497188|text|function+str_replace_once($search,+$replace,+$subject)+{
++++$pos+=+strpos($subject,+$search);
++++if+($pos+===+false)+{
++++++++return+$subject;
++++}

++++return+substr($subject,+0,+$pos)+.+$replace+.+substr($subject,+$pos+%2B+strlen($search));
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1497189|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>function str_replace_once($search, $replace, $subject) {
 $pos = strpos($subject, $search);
 if ($pos === false) {
 return $subject;
 }

 return substr($subject, 0, $pos) . $replace . substr($subject, $pos + strlen($search));
}
</code></pre>

blocks|key|197299|text|=>代码已修改，因此考虑某些注释太旧|type|unstyled|depth|inlineStyleRanges|entityRanges|data|197300|197301|和感谢每个人帮助我改进了这一点|blockquote|offset|length|style|BOLD|197302|197303|如果有BUG，请告诉我，我会马上修复的|197304|197305|所以，让我们来看看：|197306|例如，将第一个'o'替换为'ea'：|197307|$s='I+love+you';
$s=str_replace_first('o','ea',$s);
echo+$s;

//output:+I+leave+you|code-block|syntax|javascript|197308|函数：|197309|function+str_replace_first($this,$that,$s)
+++++++++{
+++++++++$w=strpos($s,$this);
+++++++++if($w===false)return+$s;
+++++++++return+substr($s,0,$w).$that.substr($s,$w%2Bstrlen($this));
+++++++++}|197310|entityMap^0|0|0|1|5|0|0|0|0|0|7|3|D|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|13|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|14|8|@$F|15|G|16|H|I]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|17|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|18|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|19|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|1A|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1B|8|@$F|1C|G|1D|H|I]|$F|1E|G|1F|H|I]]|9|@]|A|$]]|$1|R|3|S|5|T|7|1G|8|@]|9|@]|A|$U|V]]|$1|W|3|X|5|6|7|1H|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|T|7|1I|8|@]|9|@]|A|$U|V]]|$1|10|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]]|11|$]]

=&gt; CODE WAS REVISED, so consider some comments too old
<blockquote>
And thanks everyone on helping me to improve that
Any BUG, please communicate me; I'll fix that up right after
</blockquote>
So, lets go for:
Replacing the first 'o' to 'ea' for example:
<pre><code>$s='I love you';
$s=str_replace_first('o','ea',$s);
echo $s;

//output: I leave you
</code></pre>
The function:
<pre><code>function str_replace_first($this,$that,$s)
 {
 $w=strpos($s,$this);
 if($w===false)return $s;
 return substr($s,0,$w).$that.substr($s,$w+strlen($this));
 }
</code></pre>

blocks|key|197579|text|这个函数很大程度上受到了@renocor答案的启发。它使函数的多字节安全。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|197580|function+str_replace_limit($search,+$replace,+$string,+$limit)
{
++++$i+=+0;
++++$searchLength+=+mb_strlen($search);

++++while(($pos+=+mb_strpos($string,+$search))+!==+false+&&+$i+<+$limit)
++++{
++++++++$string+=+mb_substr_replace($string,+$replace,+$pos,+$searchLength);
++++++++$i+%2B=+1;
++++}

++++return+$string;
}

function+mb_substr_replace($string,+$replacement,+$start,+$length+=+null,+$encoding+=+null)
{
++++$string+=+(array)$string;
++++$encoding+=+is_null($encoding)+?+mb_internal_encoding()+:+$encoding;
++++$length+=+is_null($length)+?+mb_strlen($string)+-+$start+:+$length;

++++$string+=+array_map(function($str)+use+($replacement,+$start,+$length,+$encoding){

++++++++$begin+=+mb_substr($str,+0,+$start,+$encoding);
++++++++$end+=+mb_substr($str,+($start+%2B+$length),+mb_strlen($str),+$encoding);

++++++++return+$begin+.+$replacement+.+$end;

++++},+$string);

++++return+(+count($string)+===+1+)+?+$string[0]+:+$string;
}|code-block|syntax|javascript|197581|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This function is heavily inspired by the answer by @renocor.
It makes the function multi byte safe.

<pre><code>function str_replace_limit($search, $replace, $string, $limit)
{
 $i = 0;
 $searchLength = mb_strlen($search);

 while(($pos = mb_strpos($string, $search)) !== false &amp;&amp; $i &lt; $limit)
 {
 $string = mb_substr_replace($string, $replace, $pos, $searchLength);
 $i += 1;
 }

 return $string;
}

function mb_substr_replace($string, $replacement, $start, $length = null, $encoding = null)
{
 $string = (array)$string;
 $encoding = is_null($encoding) ? mb_internal_encoding() : $encoding;
 $length = is_null($length) ? mb_strlen($string) - $start : $length;

 $string = array_map(function($str) use ($replacement, $start, $length, $encoding){

 $begin = mb_substr($str, 0, $start, $encoding);
 $end = mb_substr($str, ($start + $length), mb_strlen($str), $encoding);

 return $begin . $replacement . $end;

 }, $string);

 return ( count($string) === 1 ) ? $string[0] : $string;
}
</code></pre>

blocks|key|1267985|text|作为对人们所说的补充，请记住整个字符串是一个数组：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1267986|$string+=+"Lorem+ipsum+lá+lá+lá";

$string[0]+=+"B";

echo+$string;|code-block|syntax|javascript|1267987|"Borem+ipsum+lálálá“|1267988|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Complementing what people said, remember that the entire string is an array:

<pre><code>$string = "Lorem ipsum lá lá lá";

$string[0] = "B";

echo $string;
</code></pre>

"Borem ipsum lá lá lá"

blocks|key|1497243|text|$str+=+"Hello+there+folks!"
$str_ex+=+explode("there,+$str,+2);+++//explodes+$string+just+twice
++++++++++++++++++++++++++++++++++++++//outputs:+array+("Hello+",+"+folks")
$str_final+=+implode("",+$str_ex);++++//+glues+above+array+together
++++++++++++++++++++++++++++++++++++++//+outputs:+str("Hello++folks")|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1497244|有一个额外的空间，但这并不重要，因为它是背景脚本在我的情况下。|unstyled|1497245|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>$str = "Hello there folks!"
$str_ex = explode("there, $str, 2); //explodes $string just twice
 //outputs: array ("Hello ", " folks")
$str_final = implode("", $str_ex); // glues above array together
 // outputs: str("Hello folks")
</code></pre>

There is one more additional space but it didnt matter as it was for backgound script in my case.

blocks|key|197633|text|如果字符串不包含任何多字节字符，并且只想替换一个字符，则可以简单地使用strpos|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|197634|这里是一个处理错误的函数|197635|/**
+*+Replace+the+first+occurence+of+given+string
+*
+*+@param++string+$search++a+char+to+search+in+`$subject`
+*+@param++string+$replace+a+char+to+replace+in+`$subject`
+*+@param++string+$subject
+*+@return+string
+*
+*+@throws+InvalidArgumentException+if+`$search`+or+`$replace`+are+invalid+or+if+`$subject`+is+a+multibytes+string
+*/
function+str_replace_first(string+$search+,+string+$replace+,+string+$subject)+:+string+{
++++//+check+params
++++if(strlen($replace)+!=+1+%7C%7C+strlen($search)+!=+1)+{
++++++++throw+new+InvalidArgumentException('$search+&+$replace+must+be+char');
++++}elseif(mb_strlen($subject)+!=+strlen($subject)){
++++++++throw+new+InvalidArgumentException('$subject+is+an+multibytes+string');
++++}
++++//+search+
++++$pos+=+strpos($subject,+$search);
++++if($pos+===+false)+{
++++++++//+not+found
++++++++return+$subject;
++++}

++++//+replace
++++$subject[$replace]+=+$subject;

++++return+$subject;
}|code-block|syntax|javascript|197636|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/function.strpos.php^0|Z|6|Z|6|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|11|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

If you string does not contains any multibyte characters and if you want to replace only one char you can simply use <a href="http://php.net/manual/en/function.strpos.php" rel="nofollow noreferrer"><code>strpos</code></a>

Here a function who handle errors

<pre><code>/**
 * Replace the first occurence of given string
 *
 * @param string $search a char to search in `$subject`
 * @param string $replace a char to replace in `$subject`
 * @param string $subject
 * @return string
 *
 * @throws InvalidArgumentException if `$search` or `$replace` are invalid or if `$subject` is a multibytes string
 */
function str_replace_first(string $search , string $replace , string $subject) : string {
 // check params
 if(strlen($replace) != 1 || strlen($search) != 1) {
 throw new InvalidArgumentException('$search &amp; $replace must be char');
 }elseif(mb_strlen($subject) != strlen($subject)){
 throw new InvalidArgumentException('$subject is an multibytes string');
 }
 // search 
 $pos = strpos($subject, $search);
 if($pos === false) {
 // not found
 return $subject;
 }

 // replace
 $subject[$replace] = $subject;

 return $subject;
}
</code></pre>

blocks|key|197646|text|For+Loop解决方案|type|unstyled|depth|inlineStyleRanges|entityRanges|data|197647|<?php
echo+replaceFirstMatchedChar("&",+"?",+"/property/details&id=202&test=123#tab-6");

function+replaceFirstMatchedChar($searchChar,+$replaceChar,+$str)
{
++++for+($i+=+0;+$i+<+strlen($str);+$i%2B%2B)+{

++++++++if+($str[$i]+==+$searchChar)+{
++++++++++++$str[$i]+=+$replaceChar;
++++++++++++break;
++++++++}
++++}
++++return+$str;
}|code-block|syntax|javascript|197648|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For Loop Solution

<pre><code>&lt;?php
echo replaceFirstMatchedChar("&amp;", "?", "/property/details&amp;id=202&amp;test=123#tab-6");

function replaceFirstMatchedChar($searchChar, $replaceChar, $str)
{
 for ($i = 0; $i &lt; strlen($str); $i++) {

 if ($str[$i] == $searchChar) {
 $str[$i] = $replaceChar;
 break;
 }
 }
 return $str;
}
</code></pre>

blocks|key|4484524|text|$str+=+"/property/details&id=202&test=123#tab-6p";
$position+=+strpos($str,"&");
echo+substr_replace($str,"?",$position,1);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4484525|使用substr_replace，我们只能替换字符串中出现的第一个字符。因为&重复了很多次，但只在第一个位置，我们必须用？|unstyled|4484526|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>$str = "/property/details&amp;id=202&amp;test=123#tab-6p";
$position = strpos($str,"&amp;");
echo substr_replace($str,"?",$position,1);
</code></pre>

Using substr_replace we can replace the occurrence of first character only in string.
as &amp; is repeated multiple times but only at first position we have to replace &amp; with ?

I want a version of <code>str_replace()</code> that only replaces the first occurrence of <code>$search</code> in the <code>$subject</code>. Is there an easy solution to this, or do I need a hacky solution?

Using str_replace so that it only acts on the first match?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我想要一个只替换$subject中第一次出现的$search的str_replace()版本。有没有一个简单的解决方案，或者我需要一个老套的解决方案？

问是否使用str_replace使其仅在第一个匹配时起作用？
EN

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问是否使用str_replace使其仅在第一个匹配时起作用？EN