As you are replacing all with the same, you could do either pass an array

$content = preg_replace(array($pattern1,$pattern2, $pattern3), '', $content);

or create one expression:

$content = preg_replace('/regexp1|regexp2|regexp3/', '', $content);

If the "expressions" are actually pure character strings, use str_replace instead.

I think you will need to incorporate word boundaries with a regex-based function.

Consider this strtr() demo:

$string="Rah rah, sis boom bah, I read a book on budweiser";
$p1 = array('sis','boom','bah');
$r1 = 'cheers';
$p2 = array('boo','hiss');
$r2 = 'jeers' ;
$p3 = array('guinness','heineken','budweiser');
$r3 = 'beers';

$replacements=array_merge(
    array_combine($p1,array_fill(0,sizeof(r1)),
    array_combine($p2,array_fill(0,sizeof(r2)),
    array_combine($p3,array_fill(0,sizeof(r3))
);
echo strtr($string,$replacements);

Output:

Rah rah, cheers cheers cheers, I read a jeersk on beers
//                                      ^^^^^ Oops

You will just need to implode your needle elements using pipes and wrap them in a non-capturing group so that the word boundaries apply to all substrings, like this:

Code: (Demo)

$string="Rah rah, sis boom bah, I read a book on budweiser";
$p1 = ['sis','boom','bah'];
$r1 = 'cheers';
$p2 = ['boo','hiss'];
$r2 = 'jeers' ;
$p3 = ['guinness','heineken','budweiser'];
$r3 = 'beers';
$find=['/\b(?:'.implode('|',p2).')\b/','/\b(?:'.implode('|',swap=[r2,$r3];
var_export($find);
echo "\n";
var_export($swap);
echo "\n";
echo preg_replace($find,$swap,$string);

Output:

array (
  0 => '/\\b(?:sis|boom|bah)\\b/',                 // unescaped: /\b(?:sis|boom|bah)\b/
  1 => '/\\b(?:boo|hiss)\\b/',                     // unescaped: /\b(?:boo|hiss)\b/
  2 => '/\\b(?:guinness|heineken|budweiser)\\b/',  // unescaped: /\b(?:guinness|heineken|budweiser)\b/
)
array (
  0 => 'cheers',
  1 => 'jeers',
  2 => 'beers',
)
Rah rah, cheers cheers cheers, I read a book on beers

*Notes:

The word boundaries \b ensure that whole words are match, avoiding unintended mismatches.

If you need case-insensitivity, just use the i flag at the end of each regex pattern. e.g. /\b(?:sis|boom|bah)\b/i

Use a callback, you can detect which pattern matched by using capturing groups, like (?:(patternt1)|(pattern2)|(etc), only the matching patterns capturing group(s) will be defined.

The only problem with that is that your current capturing groups would be shifted. To fix (read workaround) that you could use named groups. (A branch reset (?|(foo)|(bar)) would work (if supported in your version), but then you'd have to detect which pattern has matched using some other way.)

Example

function replace_callback($matches){
    if(isset($matches["m1"])){
        return "foo";
    }
    if(isset($matches["m2"])){
        return "bar";
    }
    if(isset($matches["m3"])){
        return "baz";
    }
    return "something is wrong ;)";
}

$re = "/(?|(?:regex1)(?<m1>)|(?:reg(\\s*)ex|2)(?<m2>)|(?:(back refs) work as intended \\1)(?<m3>))/";

$rep_string = preg_replace_callback($re, "replace_callback", $string);

Not tested (don't have PHP here), but something like this could work.

It looks like you're trying to generate a string that can be used as a URL.

There a numerous of scenarios that can happen when a user adds a title that you want to convert to a URL safe string. Someone could for instance use this:

Mess'd up --text-- just (to) stress /test/ ?our! `little` \\clean\\
url fun.ction!?-->"); 

Should return:

messd-up-text-just-to-stress-test-our-little-clean-url-function

Is your code ready for that? In that case you can use this function:

setlocale(LC_ALL, 'en_US.UTF8');
function toAscii(replace=array(), $delimiter='-') {
    if( !empty($replace) ) {
        $str = str_replace((array)$replace, ' ', $str);
    }

    $clean = iconv('UTF-8', 'ASCII//TRANSLIT', clean = preg_replace("/[^a-zA-Z0-9\/_|+ -]/", '', $clean);
    $clean = strtolower(trim($clean, '-'));
    $clean = preg_replace("/[\/_|+ -]+/", $delimiter, $clean);

    return $clean;
}

preg_replace can take an array just like str_replace

$string = 'I have a match1 and a match3, and here\'s a match2';
$find = ['/match1/', '/match2/'];
$replace = ['foo', 'bar'];

$result = preg_replace($find, $replace, $string);

I think this is what you are looking for

if (preg_match('@^/((?!blog|tag)[^/]+)/(?:page/)?\d+@', $_SERVER['REQUEST_URI'], $m)) {
    wp_redirect("/$m[1]", 301);
}

The regexp uses lookahead to make sure that the first match isn't blog or tag.

The '[^/]+' part matches anything that isn't a forward slash (/).

(?:page/)? - Makes an optional match against 'page/'

\d+ - Match against any number.

This will not redirect '/blog/2 if you want '/blog/2' to be redirected but not '/blog/page/2' then change the regexp above to read 'blog/page' where it now says 'blog'.

PS: I know this is 5 months old and you have probably moved on by now but I'll put this here anyway in case someone else needs help with the same issue.

Try making the pattern lazy:

$str = 'A *word* is a *word*, and this is another *word*.';
$out = preg_replace('/\*([^$]+?)\*/', '<b>$1</b>', $str);
echo $out;               //  ^^ change here

This prints:

A <b>word</b> is a <b>word</b>, and this is another <b>word</b>.

For an explanation of the minor change to your regex, the updated pattern says to:

\*        match *
([^$]+?)  followed by any character which is NOT $, one or more times,
          until reaching the
\*        FIRST closing *