Php only replaces the string that appears for the first time

In php, we usually replace all the specified characters in the replacement string at a time, such as the str_replace function, but sometimes we only want to replace the first occurrence, such as the keyword in the article, if there are 100 characters

In php, we usually replace all the specified characters in the replacement string at a time, such as the str_replace function, but sometimes we only want to replace the first occurrence, such as replacing the keyword in the article, if there are 100 such cases that cannot be used for 100 times, I just want to limit them a few times. next I will introduce the implementation method to you.

Example:$ Str = 'here is the string. I will only replace the ABC after ABC once. I will not replace it .';

Replace the first abc with xyz. because the string to be replaced is fixed, many people think of using the str_replace () function to see if this function is required.

Str_replace (mixed $ search, mixed $ replace, mixed $ subject [, int & $ count])

Accidentally, I thought it was what we wanted. the last parameter was the total number of times the replacement was returned. it was a reference variable, instead of the number of times it would be replaced, therefore, str_replace () cannot be used.

Preg_replace () can be implemented. Unfortunately, regular expressions are used. the code is as follows:

$ Str = preg_replace ('/abc/', 'ABC', $ str, 1); echo $ str;

Example:The email is hidden four digits forward from the first two digits (inclusive) of @. the code is as follows:

1. Function show_email_2 ($ string ){
2. $ First = strpos ($ string ,'@');
3. // Var_dump ($ first );
4. If ($ first = 1 ){
5. $ String = '****'. $ string;
6. }
7. If ($ first> 1 & $ first <= 5 ){
8. $ String = substr_replace ($ string, '*****', 0, $ first-1 );
9. }
10. If ($ first> 5 ){
11. $ String = substr_replace ($ string, '*****', $ first-5, 4 );
12. }
14. Var_dump ($ string );
15. Return $ string;
16. }
17. // Show_email_2 ('22 @ 163.com '); // output --> *** 2@163.com
18. // Show_email_2 ('22 @ 22.com '); // output --> *** 2@22.com
19. Show_email_2 ('1970 @ 163.com '); // output --> 61 **** 6@163.com

Is there any regex? well, you can.

1. $ Replace = 'XYZ ';
2. If ($ position = strpos ($ str, $ replace ))! = False ){
3. $ Leng = strlen ($ replace );
4. $ Str = substr_replace ($ str, 'ABC', $ position, $ leng );
5. }
6. Echo $ str;

If you want to replace it with a specified number of times, refer to the following method. the code is as follows:

2. /*
3. * $ Text is the input text;
4. * $ Word is the original string;
5. * $ Cword is the string to be replaced;
6. * $ Pos indicates the position where $ word appears N times in $ text, starting from 1.
7. **/
8. Function changeNstr ($ text, $ word, $ cword, $ pos = 1 ){
9. $ Text_array = explode ($ word, $ text );
10. $ Num = count ($ text_array)-1;
11. If ($ pos> $ num ){
12. Return "the number is too big! Or can not find the $ word ";
13. }
14. $ Result_str = '';
15. For ($ I = 0; $ I <= $ num; $ I ++ ){
16. If ($ I ==$ pos-1 ){
17. $ Result_str. = $ text_array [$ I]. $ cword;
18. } Else {
19. $ Result_str. = $ text_array [$ I]. $ word ;}
20. }
21. Return rtrim ($ result_str, $ word );
22. }
23. $ Text = 'Hello world hello pig hello cat hello dog hello small boys ';
24. $ Word = 'hello ';
25. $ Cword = 'good-bye ';
26. Echo changeNstr ($ text, $ word, $ cword, 3 );
27. // Output: hello world hello pig good-bye cat hello dog hello small boy
28. ?>

The instance is easy to understand. if you don't want to know more about it, we can simply use str_replace.