How to Check if a String Contains a Substring in PHP

  1. Use the strpos() Function to Check if a String Contains a Substring in PHP
  2. Use the preg_match() Function to Check if a String Contains a Substring in PHP

This article will introduce different methods to check if a string contains a substring in PHP using the strpos() and preg_match() functions.

Use the strpos() Function to Check if a String Contains a Substring in PHP

We will use the built-in function strpos() to check if a string contains a substring. This command checks the occurrence of a passed substring; the correct syntax to execute this is as follows:

strpos($originalString, $checkString, $offset);

The built-in function strpos() has three parameters, which are discussed below:

Parameters Description
$originalString mandatory It’s the string that we want to check for the substring.
$checkString mandatory It’s the string that we want to check in the $checkString.
$offset optional It’s the start position of the search process; if the offset is negative, the search process will start from the end.

This function returns the position of the substring relative to the position of the original string. The program below shows how we can use the strpos() function to check if a string contains a substring.

<?php
$mystring = "This is a PHP program.";

if (strpos($mystring, "program.") !== false) {
    echo("True");
}
?>

Output:

True

If we pass the $offset parameter, the function will start the search from the specified location.

<?php
$mystring = "This is a PHP program.";

if (strpos($mystring, "PHP", 13) !== false) {
    echo("True");
} else {
    echo("False");
}
?>

Output:

False

The output has shown False because the string that we searched was before the offset.

Use the preg_match() Function to Check if a String Contains a Substring in PHP

In PHP, we can also use the preg_match() function to check if a string contains a specific word. This function uses regular expressions to match patterns. The correct syntax to use this function is as follows:

preg_match($pattern, $inputString, $matches, $flag, $offset);

The function preg_match() accepts five parameters. The detail of its parameters is as follows

Parameters Description
$regexPattern mandatory It is the pattern which we will search in the original string.
$string mandatory It is the string which we will search in the original string.
$matches optional This parameter stores the result of the matching process in it.
$flag optional This parameter specifies the flags. We have two flags for this parameter: PREG_OFFSET_CAPTURE and PREG_UNMATCHED_AS_NULL.
$offset optional This parameter tells about the start position of the matching process.

We will use the pattern /{$search}/i to check for a specific word. The program that checks if a string contains a specific word is as follows:

<?php
$mystring = "This is a php program.";
$search = "a";
if(preg_match("/{$search}/i", $mystring)) {
    echo "True"; } else {
    echo("False");
}
?>

Output:

True

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