How do I check if a string contains a specific word in PHP?

You could use regular expressions. It would look something like this:

$a = 'How are you?';

if (preg_match('/are/',$a))
    echo 'true';

Don't tell me it's bad just because you've heard it's bad before. You might if you have any facts to back it up though ;)

On the performance side, strpos is about three times faster and have in mind, when I did one million compares at once, it took preg match 1.5 seconds to finish and for strpos it took 0.5 seconds. What I'm trying to say is that it runs really fast either way. If you don't have 100,000 visitors every second, you shouldn't concern yourself with this kind of stuff and take what's most comfortable, IMO.

Use strpos function:

if (strpos($a, 'are') !== false)
    echo 'true';

Here is a little utility function that is useful in situations like this

// returns true if $needle is a substring of $haystack
function contains($needle, $haystack)
{
    return strpos($haystack, $needle) !== false;
}

To determine whether a string contains another string you can use the PHP function strpos().

int strpos ( string $haystack , mixed $needle [, int $offset = 0 ] )

<?php

$haystack = 'how are you';
$needle = 'are';

if (strpos($haystack,$needle) !== false) {
    echo '$haystack contains $needle';
}

?>

CAUTION:

If the needle you are searching for is at the beginning of the haystack it will return position 0, if you do a == compare that will not work, you will need to do a ===

A == sign is a comparison and tests whether the variable / expression / constant to the left has the same value as the variable / expression / constant to the right.

A === sign is a comparison to see whether two variables / expresions / constants are equal AND have the same type - i.e. both are strings or both are integers.

While most of these answers will tell you if a substring appears in your string, that's usually not what you want if you're looking for a particular word, and not a substring.

What's the difference? Substrings can appear within other words:

• The "are" at the beginning of "area"
• The "are" at the end of "hare"
• The "are" in the middle of "fares"

One way to mitigate this would be to use a regular expression coupled with word boundaries (\b):

function containsWord($str, $word)
{
    return !!preg_match('#\\b' . preg_quote($word, '#') . '\\b#i', $str);
}

This method doesn't have the same false positives noted above, but it does have some edge cases of its own. Word boundaries match on non-word characters (\W), which are going to be anything that isn't a-z, A-Z, 0-9, or _. That means digits and underscores are going to be counted as word characters and scenarios like this will fail:

• The "are" in "What _are_ you thinking?"
• The "are" in "lol u dunno wut those are4?"

If you want anything more accurate than this, you'll have to start doing English language syntax parsing, and that's a pretty big can of worms (and assumes proper use of syntax, anyway, which isn't always a given).

Using strstr() or stristr() if your search should be case insensitive would be another option.

Look at strpos():

<?php
    $mystring = 'abc';
    $findme   = 'a';
    $pos = strpos($mystring, $findme);

    // Note our use of ===. Simply, == would not work as expected
    // because the position of 'a' was the 0th (first) character.
    if ($pos === false) {
        echo "The string '$findme' was not found in the string '$mystring'.";
    }
    else {
        echo "The string '$findme' was found in the string '$mystring',";
        echo " and exists at position $pos.";
    }
?>

Make use of case-insensitve matching using stripos():

if (stripos($string,$stringToSearch) !== false) {
    echo 'true';
}

If you want to avoid the "falsey" and "truthy" problem, you can use substr_count:

if (substr_count($a, 'are') > 0) {
    echo "at least one 'are' is present!";
}

It's a bit slower than strpos but it avoids the comparison problems.

Another option is to use the strstr() function. Something like:

if (strlen(strstr($haystack,$needle))>0) {
// Needle Found
}

Point to note: The strstr() function is case-sensitive. For a case-insensitive search, use the stristr() function.

Peer to SamGoody and Lego Stormtroopr comments.

If you are looking for a php algorithm to rank search results based on proximity/relevance of multiple words here comes a quick and easy way of generating search results with PHP only:

Issues with the other boolean search methods sush as strpos(), preg_match(), strstr() or stristr()

1. can't search for multiple words
2. results are unranked

PHP method based on Vector Space Model and tf-idf (term frequency–inverse document frequency):

It sounds difficult but is surprisingly easy.

If we want to search for multiple words in a string the core problem is how we assign a weight to each one of them?

If we could weight the terms in a string based on how representative they are of the string as a whole, we could order our results by the ones that best match the query.

This is the idea of the vector space model, not far from how SQL fulltext search works:

function get_corpus_index($corpus = array(), $separator=' ') {

    $dictionary = array();

    $doc_count = array();

    foreach($corpus as $doc_id => $doc) {

        $terms = explode($separator, $doc);

        $doc_count[$doc_id] = count($terms);

        // tf–idf, short for term frequency–inverse document frequency, 
        // according to wikipedia is a numerical statistic that is intended to reflect 
        // how important a word is to a document in a corpus

        foreach($terms as $term) {

            if(!isset($dictionary[$term])) {

                $dictionary[$term] = array('document_frequency' => 0, 'postings' => array());
            }
            if(!isset($dictionary[$term]['postings'][$doc_id])) {

                $dictionary[$term]['document_frequency']++;

                $dictionary[$term]['postings'][$doc_id] = array('term_frequency' => 0);
            }

            $dictionary[$term]['postings'][$doc_id]['term_frequency']++;
        }

        //from http://phpir.com/simple-search-the-vector-space-model/

    }

    return array('doc_count' => $doc_count, 'dictionary' => $dictionary);
}

function get_similar_documents($query='', $corpus=array(), $separator=' '){

    $similar_documents=array();

    if($query!=''&&!empty($corpus)){

        $words=explode($separator,$query);

        $corpus=get_corpus_index($corpus, $separator);

        $doc_count=count($corpus['doc_count']);

        foreach($words as $word) {

            if(isset($corpus['dictionary'][$word])){

                $entry = $corpus['dictionary'][$word];


                foreach($entry['postings'] as $doc_id => $posting) {

                    //get term frequency–inverse document frequency
                    $score=$posting['term_frequency'] * log($doc_count + 1 / $entry['document_frequency'] + 1, 2);

                    if(isset($similar_documents[$doc_id])){

                        $similar_documents[$doc_id]+=$score;

                    }
                    else{

                        $similar_documents[$doc_id]=$score;

                    }
                }
            }
        }

        // length normalise
        foreach($similar_documents as $doc_id => $score) {

            $similar_documents[$doc_id] = $score/$corpus['doc_count'][$doc_id];

        }

        // sort fro  high to low

        arsort($similar_documents);

    }   

    return $similar_documents;
}

CASE 1

$query = 'are';

$corpus = array(
    1 => 'How are you?',
);

$match_results=get_similar_documents($query,$corpus);
echo '<pre>';
    print_r($match_results);
echo '</pre>';

RESULT

Array
(
    [1] => 0.52832083357372
)

CASE 2

$query = 'are';

$corpus = array(
    1 => 'how are you today?',
    2 => 'how do you do',
    3 => 'here you are! how are you? Are we done yet?'
);

$match_results=get_similar_documents($query,$corpus);
echo '<pre>';
    print_r($match_results);
echo '</pre>';

RESULTS

Array
(
    [1] => 0.54248125036058
    [3] => 0.21699250014423
)

CASE 3

$query = 'we are done';

$corpus = array(
    1 => 'how are you today?',
    2 => 'how do you do',
    3 => 'here you are! how are you? Are we done yet?'
);

$match_results=get_similar_documents($query,$corpus);
echo '<pre>';
    print_r($match_results);
echo '</pre>';

RESULTS

Array
(
    [3] => 0.6813781191217
    [1] => 0.54248125036058
)

There are plenty of improvements to be made but the model provides a way of getting good results from natural queries, which don't have boolean operators sush as strpos(), preg_match(), strstr() or stristr().

NOTA BENE

Optionally eliminating redundancy prior to search the words

• thereby reducing index size and resulting in less storage requirement

• less disk I/O

• faster indexing and a consequently faster search.

1. Normalisation

• Convert all text to lower case

2. Stop word elimination

• Eliminate words from the text which carry no real meaning (like 'and', 'or', 'the', 'for', etc.)

3. Dictionary substitution

• Replace words with others which have an identical or similar meaning. (ex:replace instances of 'hungrily' and 'hungry' with 'hunger')

• Further algorithmic measures (snowball) may be performed to further reduce words to their essential meaning.

• The replacement of colour names with their hexadecimal equivalents

• The reduction of numeric values by reducing precision are other ways of normalising the text.

RESOURCES

• http://linuxgazette.net/164/sephton.html
• http://snowball.tartarus.org/
• MySQL Fulltext Search Score Explained
• http://dev.mysql.com/doc/internals/en/full-text-search.html
• http://en.wikipedia.org/wiki/Vector_space_model
• http://en.wikipedia.org/wiki/Tf%E2%80%93idf
• http://phpir.com/simple-search-the-vector-space-model/

The function below also works and does not depend on any other function; it uses only native PHP string manipulation. Personally, I do not recommend this, but you can see how it works:

<?php

if (!function_exists('is_str_contain')) {
  function is_str_contain($string, $keyword)
  {
    if (empty($string) || empty($keyword)) return false;
    $keyword_first_char = $keyword[0];
    $keyword_length = strlen($keyword);
    $string_length = strlen($string);

    // case 1
    if ($string_length < $keyword_length) return false;

    // case 2
    if ($string_length == $keyword_length) {
      if ($string == $keyword) return true;
      else return false;
    }

    // case 3
    if ($keyword_length == 1) {
      for ($i = 0; $i < $string_length; $i++) {

        // Check if keyword's first char == string's first char
        if ($keyword_first_char == $string[$i]) {
          return true;
        }
      }
    }

    // case 4
    if ($keyword_length > 1) {
      for ($i = 0; $i < $string_length; $i++) {
        /*
        the remaining part of the string is equal or greater than the keyword
        */
        if (($string_length + 1 - $i) >= $keyword_length) {

          // Check if keyword's first char == string's first char
          if ($keyword_first_char == $string[$i]) {
            $match = 1;
            for ($j = 1; $j < $keyword_length; $j++) {
              if (($i + $j < $string_length) && $keyword[$j] == $string[$i + $j]) {
                $match++;
              }
              else {
                return false;
              }
            }

            if ($match == $keyword_length) {
              return true;
            }

            // end if first match found
          }

          // end if remaining part
        }
        else {
          return false;
        }

        // end for loop
      }

      // end case4
    }

    return false;
  }
}

Test:

var_dump(is_str_contain("test", "t")); //true
var_dump(is_str_contain("test", "")); //false
var_dump(is_str_contain("test", "test")); //true
var_dump(is_str_contain("test", "testa")); //flase
var_dump(is_str_contain("a----z", "a")); //true
var_dump(is_str_contain("a----z", "z")); //true 
var_dump(is_str_contain("mystringss", "strings")); //true 

I'm a bit impressed that none of the answers here that used strpos, strstr and similar functions mentioned Multibyte String Functions yet (2015-05-08).

Basically, if you're having trouble finding words with characters specific to some languages, such as German, French, Portuguese, Spanish, etc. (e.g.: ä, é, ô, ç, º, ñ), you may want to precede the functions with mb_. Therefore, the accepted answer would use mb_strpos or mb_stripos (for case-insensitive matching) instead:

if (mb_strpos($a,'are') !== false) {
    echo 'true';
}

If you cannot guarantee that all your data is 100% in UTF-8, you may want to use the mb_ functions.

A good article to understand why is The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!) by Joel Spolsky.

if (preg_match('are', $a)) {
   echo 'true';
}

I had some trouble with this, and finally I chose to create my own solution. Without using regular expression engine:

function contains($text, $word)
{
    $found = false;
    $spaceArray = explode(' ', $text);

    $nonBreakingSpaceArray = explode(chr(160), $text);

    if (in_array($word, $spaceArray) ||
        in_array($word, $nonBreakingSpaceArray)
       ) {

        $found = true;
    }
    return $found;
 }

You may notice that the previous solutions are not an answer for the word being used as a prefix for another. In order to use your example:

$a = 'How are you?';
$b = "a skirt that flares from the waist";
$c = "are";

With the samples above, both $a and $b contains $c, but you may want your function to tell you that only $a contains $c.

$a = 'how are you';
if (strpos($a,'are')) {
    echo 'true';
}

Another option to finding the occurrence of a word from a string using strstr() and stristr() is like the following:

<?php
    $a = 'How are you?';
    if (strstr($a,'are'))  // Case sensitive
        echo 'true';
    if (stristr($a,'are'))  // Case insensitive
        echo 'true';
?>

You should use case Insensitive format,so if the entered value is in small or caps it wont matter.

<?php
$grass = "This is pratik joshi";
$needle = "pratik";
if (stripos($grass,$needle) !== false) { 

 /*If i EXCLUDE : !== false then if string is found at 0th location, 
   still it will say STRING NOT FOUND as it will return '0' and it      
   will goto else and will say NOT Found though it is found at 0th location.*/
    echo 'Contains word';
}else{
    echo "does NOT contain word";
}
?>

Here stripos finds needle in heystack without considering case (small/caps).

PHPCode Sample with output

The short-hand version

$result = false!==strpos($a, 'are');

In order to find a 'word', rather than the occurrence of a series of letters that could in fact be a part of another word, the following would be a good solution.

$string = 'How are you?';
$array = explode(" ", $string);

if (in_array('are', $array) ) {
    echo 'Found the word';
}

Maybe you could use something like this:

<?php
    findWord('Test all OK');

    function findWord($text) {
        if (strstr($text, 'ok')) {
            echo 'Found a word';
        }
        else
        {
            echo 'Did not find a word';
        }
    }
?>

You can use the strstr function:

$haystack = "I know programming";
$needle   = "know";
$flag = strstr($haystack, $needle);

if ($flag){

    echo "true";
}

Without using inbuilt function:-

$haystack  = "hello world";
$needle = "llo";

$i = $j = 0;

while( isset($needle[$i]) ){
    while( isset($haystack[$j]) && ( $needle[$i] != $haystack[$j] )  ){
        $j++;
        $i = 0;
    }
    if( !isset($haystack[$j]) ){
        break;
    }
    $i++;
    $j++;

}
if ( !isset($needle[$i]) ){
        echo "YES";
}else{
    echo "NO ";
}

Do not use preg_match() if you only want to check if one string is contained in another string. Use strpos() or strstr() instead as they will be faster. (http://in2.php.net/preg_match)

if (strpos($text, 'string_name') !== false){
   echo 'get the string';
}

It can be done in three different ways:

 $a = 'How are you?';

1- stristr()

 if (strlen(stristr($a,"are"))>0) {
    echo "true"; // are Found
 } 

2- strpos()

 if (strpos($a, "are") !== false) {
   echo "true"; // are Found
 }

3- preg_match()

 if( preg_match("are",$a) === 1) {
   echo "true"; // are Found
 }

You need to use identical/not identical operators because strpos can return 0 as it's index value. If you like ternary operators, consider using the following (seems a little backwards I'll admit):

echo FALSE === strpos($a,'are') ? 'false': 'true';

If you want to check if the string contains several specifics words, you can do:

$badWords = array("dette", "capitale", "rembourser", "ivoire", "mandat");

$string = "a string with the word ivoire";

$matchFound = preg_match_all("/\b(" . implode($badWords,"|") . ")\b/i", $string, $matches);

if ($matchFound) {
    echo "a bad word has been found";
}
else {
    echo "your string is okay";
}

This is useful to avoid spam when sending emails for example.

Check if string contains specific words?

This means the string has to be resolved into words (see note below).

One way to do this and to specify the separators is using preg_split (doc):

<?php

function contains_word($str, $word) {
  // split string into words
  // separators are substrings of at least one non-word character
  $arr = preg_split('/\W+/', $str, NULL, PREG_SPLIT_NO_EMPTY);

  // now the words can be examined each
  foreach ($arr as $value) {
    if ($value === $word) {
      return true;
    }
  }
  return false;
}

function test($str, $word) {
  if (contains_word($str, $word)) {
    echo "string '" . $str . "' contains word '" . $word . "'\n";
  } else {
    echo "string '" . $str . "' does not contain word '" . $word . "'\n" ;
  }
}

$a = 'How are you?';

test($a, 'are');
test($a, 'ar');
test($a, 'hare');

?>

A run gives

$ php -f test.php                   
string 'How are you?' contains word 'are' 
string 'How are you?' does not contain word 'ar'
string 'How are you?' does not contain word 'hare'

Note: Here we do not mean word for every sequence of symbols.

A practical definition of word is in the sense the PCRE regular expression engine, where words are substrings consisting of word characters only, being separated by non-word characters.

A "word" character is any letter or digit or the underscore character, that is, any character which can be part of a Perl " word ". The definition of letters and digits is controlled by PCRE's character tables, and may vary if locale-specific matching is taking place (..)

In PHP, the best way to verify if a string contains a certain substring, is to use a simple helper function like this :

function contains($haystack, $needle, $caseSensitive = false) {
    return $caseSensitive ? 
            (strpos($haystack, $needle) === FALSE ? FALSE : TRUE):
            (stripos($haystack, $needle) === FALSE ? FALSE : TRUE);
}

Explanation :

• strpos finds the position of the first occurrence of a case-sensitive substring in a string
• stripos finds the position of the first occurrence of a case-insensitive substring in a string
• myFunction($haystack, $needle) === FALSE ? FALSE : TRUE ensures that myFunction always returns a boolean and fixes unexpected behavior when the index of the substring is 0
• $caseSensitive ? A : B selects either strpos or stripos to do the work, depending on the value of $caseSensitive

Output :

var_dump(contains('bare','are'));            // Outputs : bool(true)
var_dump(contains('stare', 'are'));          // Outputs : bool(true)
var_dump(contains('stare', 'Are'));          // Outputs : bool(true)
var_dump(contains('stare', 'Are', true));    // Outputs : bool(false)
var_dump(contains('hair', 'are'));           // Outputs : bool(false)
var_dump(contains('aren\'t', 'are'));        // Outputs : bool(true)
var_dump(contains('Aren\'t', 'are'));        // Outputs : bool(true)
var_dump(contains('Aren\'t', 'are', true));  // Outputs : bool(false)
var_dump(contains('aren\'t', 'Are'));        // Outputs : bool(true)
var_dump(contains('aren\'t', 'Are', true));  // Outputs : bool(false)
var_dump(contains('broad', 'are'));          // Outputs : bool(false)
var_dump(contains('border', 'are'));         // Outputs : bool(false)

A string can be checked with the below function:

function either_String_existor_not($str, $character) {
    if (strpos($str, $character) !== false) {
        return true;
    }
    return false;
}