How many times a substring occurs in a string

substr_count()

<?php
 //Syntax
 substr_count(
  string $haystack, string $needle,
  int $offset = 0, ?int $length = null
 ): int

The substr_count() function counts the number of times a substring is found in a string. To use this function, pass the string $haystack to search and a substring $needle to search for, see the following example:

<?php
 $haystack = 'functions are fun';
 $needle   = 'fun';
 $count    = substr_count ($haystack, $needle);
 echo $count; //2

The third argument (optional) is the offset to specify the index position to start searching:

<?php
 $haystack = 'functions are fun';
 $needle   = 'fun';

 //count in 'ctions are fun'
 $count    = substr_count ($haystack, $needle, 3);
 echo $count; //1

The fourth argument (optional) is the maximum length the function should search after the offset:

<?php
 $haystack = 'functions are fun';
 $needle   = 'fun';

 //Counts in 'ctions are fun'
 echo substr_count($haystack, $needle, 3, 14); //1

 //Counts in 'ctions are'
 echo substr_count($haystack, $needle, 3, 10); //0

 //Counts in 'functions '
 echo substr_count($haystack, $needle, 0, 10); //1

Note: substr_count() function generates an error if the sum of offset and length is greater than string $haystack length. See example:

<?php
 $haystack = 'functions are fun';
 $needle   = 'fun';
 $hslength = strlen($haystack); //17
 
// generates an error because 3+15 > 17
 echo substr_count($haystack, $needle, 3, 15);

You can use the negative values for the offset and length arguments, if the offset is negative, counting starts from the end of the string. A negative length counts from the end of the $haystack.

<?php
 $haystack = 'functions are fun';
 $needle   = 'fun';

 //Counts in 'fun'
 echo substr_count($haystack, $needle, -3); //1

 //Counts in 'ns are '
 echo substr_count($haystack, $needle, -10, -3); //0

 //Counts in 'function'
 echo substr_count($haystack, $needle, 0, -9); //1

Note: You can use the substr() function to see the remaining portion of the string $haystack after providing the offset and length values, for example:

<?php
 $haystack = 'functions are fun';
 $needle   = 'fun';
 $offset   = 0;
 $length   = -9;
 
 echo substr ($haystack, $offset, $length); //function
 echo '<br>';
 echo substr_count($haystack, $needle, $offset, $length);//1 

mb_substr_count()

mb_substr_count(string $haystack, string $needle, ?string $encoding = null): int

Use this function to count the number of substring occurrences in a multi-byte string:

<?php
 $haystack = '.цом, .нет, .орг, .нет';
 $needle   = 'нет';
 $encoding = 'UTF-8';
 echo mb_substr_count($haystack, $needle); //2
 echo mb_substr_count($haystack, $needle, $encoding); //2

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Manipulating substrings: