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

Answers

You can use the strpos() function which is used to find the occurrence of one string inside another one:

$a = 'How are you?';

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

Note that the use of !== false is deliberate; strpos() returns either the offset at which the needle string begins in the haystack string, or the boolean false if the needle isn't found. Since 0 is a valid offset and 0 is "falsey", we can't use simpler constructs like !strpos($a, 'are').

---

Use strpos function:

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

---

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).

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

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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.

---

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 such 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 full-text 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 from  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 such 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. Stopword 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/

---

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';
}

---

You can use the strstr function:

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

if ($flag){

    echo "true";
}

Without using an 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 ";
}

---

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';
}

---

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
 }

---

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

---

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';

---

The strpos function works fine, but if you want to do case-insensitive checking for a word in a paragraph then you can make use of the stripos function of PHP.

For example,

$result = stripos("I love PHP, I love PHP too!", "php");
if ($result === false) {
    // Word does not exist
}
else {
    // Word exists
}

Find the position of the first occurrence of a case-insensitive substring in a string.

If the word doesn't exist in the string then it will return false else it will return the position of the word.

stristr in PHP

PHP stristr() function is used  to searches its first string argument to see if its second string argument is contained in it. Returns the substring of the first string that starts with the first instance of the second argument, if any is found – otherwise it returns false.

Syntax:

stristr(string,search)
string : Required. Specifies the input string to search

search : Required. Specifies the string to search for.

Note : PHP stristr() function is binary-safe and case-insensitive. For case-sensitive search, use PHP strstr() function.

Example:

<?php
echo stristr("Good Morning world!","MORNING");
echo "<br /><strong> Example using ASCII code for search : </strong><br />";
echo stristr("Good Morning",111);
?>
Output will be:
Morning world!
Example using ASCII code for search :
ood Morning