php - Using preg_match Check IF Keyword Exists in Wordpress Post Content

I am trying to figure out how I can effectively search the post content for a keyword that can be comprised of one or multiple words ( i.e. word, two words, and three words, etc. ) and retrieved using a variable ( i.e. $meta_keyword_1, $meta_keyword_2 ).

I have a function that updates custom fields based upon the results of a keyword search. I have been successful in searching the post title for a keyword using stripos. I was NOT able to successfully use stripos to search the post content. I was able to research and come up with an example of a preg_match, but it keeps returning '0' or FALSE even when the exact match is present in the content.

Here are the processes within my function:

1). Retrieve keyword and replace "-" for " " for searching purposes:

NOTE: Meta keyword is inputted as: word, two-words, and-three-words, blue-rabbit, red-rabbit

$meta_keyword_1_clean = str_replace("-", " ", $meta_keyword_1);

$meta_keyword_2_clean = str_replace("-", " ", $meta_keyword_2);
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2). Search IF keyword exists in post content:

$post_content_strip_1 = preg_match('/('.$meta_keyword_1_clean.')/', $post->post_content);

$post_content_strip_2 = preg_match('/('.$meta_keyword_2_clean.')/', $post->post_content);
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3). Execute IF statement if keyword exists, else continue to next IF statement if does not exist:

<?php

elseif ( $post_content_strip_1 !== false  ) {

    // For testing purposes, Update post meta #1 with $post_content_strip_1 value
    // Update post meta #2 with $meta_keyword_1 value

} elseif ( $post_content_strip_2 !== false ) {

    // For testing purposes, Update post meta #1 with $post_content_strip_2 value
    // Update post meta #2 with $meta_keyword_2 value

} else {

    return false;

}
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Here are my results:

Match keywords found on post content: word, two words

Match keywords NOT found on post content: blue rabbit, red rabbit

a). Using '!== false' + $meta_keyword_1 = 'word' ( MATCH ) --> First IF statement executed, output '0' and 'word';

b). Using '!== false' + $meta_keyword_1 = 'two-words' ( MATCH ) --> First IF statement executed, output '0' and 'two-words';

c). Using '!== false' + $meta_keyword_1 = 'blue-rabbit' ( NON-MATCH ) --> First IF statement executed, output '0' and 'blue-rabbit';

d). Using '!== 0' + $meta_keyword_1 = 'word' ( MATCH ) --> Second IF statement executed, $meta_keyword_2 = two-words ( MATCH ), output '0' and 'two-words';

e). Using '!== 0' + $meta_keyword_1 = 'blue-rabbit' ( NON-MATCH ) --> Second IF statement executed, $meta_keyword_2 = red-rabbit ( NON-MATCH ), output '0' and 'red-rabbit';

f). Using '=== false' + $meta_keyword_1 = 'word' ( MATCH ) --> Second IF statement executed, $meta_keyword_2 = red-rabbit ( NON-MATCH ), output '0' and 'red-rabbit';

g). Using '=== false' + $meta_keyword_1 = 'blue-rabbit' ( NON-MATCH ) --> Second IF statement executed, $meta_keyword_2 = red-rabbit ( NON-MATCH ), output '0' and 'red-rabbit';

My problems:

1). I feel like the preg_match pattern is not properly setup to produce an accurante result of found or not-found. My previous attempts at using preg_match would not produce a value ( i.e. 0 or 1 ), with various examples I have been able to progress it this far;

2). My keywords are inputted as lowercase but post content could be varying. The searches should be case insensitive, I believe that is achieved with a '/i' at the end of the pattern?;

If you think I am missing something, please let me know. Any help would be greatly appreciated.

Thanks in advance!

UPDATE #1:

To better illustrate my problem, I believe the reason why my keyword searches of the post content are failing is because the preg_match pattern is incorrectly setup. The complication, including my lack of understanding, are the variable ( $meta_keyword_1_clean or $meta_keyword_2_clean ) that are inputted, and the modifiers that come before and after.

This produces a FALSE result always:

preg_match('/('.$meta_keyword_2_clean.')/', $post->post_content);

This and variations of it produces errors:

preg_match('/'.$meta_keyword_2_clean.'/', $post->post_content);

I am looking for help in producing this:

preg_match([something-here].$meta_keyword_2_clean.[something-here], $post->post_content);

I hope this clarifies my need.

UPDATE #2:

I decided to research a little bit more on the subject after Jan's comment ( Thank You Jan! ) and I was able to find someone that asked the same question, perhaps with much better precision. Answer to my problem here: Strpos with exact matches. I hope this helps someone else finding this question.