Searching Strings in PHP

When writing PHP scripts, you often need to search a string for a particular chunk of text. For example, you might be writing a search engine to search through pages of content, or you might want to know if a URL or email address contains a certain domain name.

PHP gives you many useful functions for searching strings. In this article you look at:

• strstr() for finding out whether some text is in a string
• strpos() and strrpos() for finding the position of some text in a string
• substr_count() for finding out how many times some text appears in a string

Simple text searching with strstr()

PHP’s strstr() function simply takes a string to search, and a chunk of text to search for. If the text was found, it returns the portion of the string from the first character of the match up to the end of the string:

$myString = 'Hello, there!';
echo strstr( $myString, 'llo' );  // Displays "llo, there!"

If the text wasn’t found then strstr() returns false. You can use this fact to determine if the text chunk was in the string or not:

$myString = 'Hello, there!';

if ( strstr( $myString, 'Goodbye' ) ) {
  echo "Text found";
} else {
  echo "Text not found";
}

The above code displays:

Text not found

Finding the position of a match: strpos() and strrpos()

strpos() takes the same 2 arguments as strstr(). However, rather than returning a portion of the string, it returns the index of the first character of the matched text in the string:

$myString = 'Hello, there!';
echo strpos( $myString, 'llo' );  // Displays "2"

In the above code, strpos() finds the text 'llo' in the target string starting at the 3rd character, so it returns 2. (Remember that character index positions in strings start from 0, not 1.)

Be careful when using strpos() to check for the existence of a match. The following code incorrectly displays “Not found”, because strpos() returns 0, which is equivalent to false in PHP:

$myString = 'Hello, there!';
if ( strpos( $myString, 'Hello' ) ) {
  echo "Found";
} else {
  echo "Not found";
}

To fix this, make sure you test explicitly for false by using the === or !== operator. The following code correctly displays “Found”:

$myString = 'Hello, there!';
if ( strpos( $myString, 'Hello' ) !== false ) {
  echo "Found";
} else {
  echo "Not found";
}

You can pass a third argument to strpos() to specify the index position from which to begin the search:

$myString = 'Hello, there!';
echo strpos( $myString, 'e' ) . '<br />';     // Displays "1"
echo strpos( $myString, 'e', 2 ) . '<br />';  // Displays "9"

The strrpos() function is very similar to strpos(). The only difference is that it finds the last match in the string instead of the first:

$myString = 'Hello, there!';
echo strpos( $myString, 'e' ) . "<br />";   // Displays "1"
echo strrpos( $myString, 'e' ) . "<br />";  // Displays "11"

Counting matches with substr_count()

You can use PHP’s substr_count() function to find the number of times a chunk of text appears in the target string:

$myString = 'Short stories';
echo substr_count( $myString, 'or' );  // Displays "2"

As with strpos() and strrpos(), you can pass an optional third argument: the index position to begin the search. For example:

$myString = 'Short stories';
echo substr_count( $myString, 'or', 6 );  // Displays "1"

You can also pass an optional fourth argument: the number of characters after the offset position in which to search for the text. For example:

echo substr_count( $myString, 'or', 0, 10 ) . '<br />';  // Displays "2"
echo substr_count( $myString, 'or', 0, 5 ) . '<br />';   // Displays "1"

In this article you’ve looked at how to search strings in PHP. You’ve explored the strstr() function for finding out whether a chunk of text exists in a string; strpos() and strrpos() for locating text in a string; and substr_count() for finding out the number of matches in a string. Happy coding!