How can strip whitespaces in PHP's variable?

A regular expression does not account for UTF-8 characters by default. The \s meta-character only accounts for the original latin set. Therefore, the following command only removes tabs, spaces, carriage returns and new lines

// http://stackoverflow.com/a/1279798/54964
$str=preg_replace('/\s+/', '', $str);

With UTF-8 becoming mainstream this expression will more frequently fail/halt when it reaches the new utf-8 characters, leaving white spaces behind that the \s cannot account for.

To deal with the new types of white spaces introduced in unicode/utf-8, a more extensive string is required to match and removed modern white space.

Because regular expressions by default do not recognize multi-byte characters, only a delimited meta string can be used to identify them, to prevent the byte segments from being alters in other utf-8 characters (\x80 in the quad set could replace all \x80 sub-bytes in smart quotes)

$cleanedstr = preg_replace(
    "/(\t|\n|\v|\f|\r| |\xC2\x85|\xc2\xa0|\xe1\xa0\x8e|\xe2\x80[\x80-\x8D]|\xe2\x80\xa8|\xe2\x80\xa9|\xe2\x80\xaF|\xe2\x81\x9f|\xe2\x81\xa0|\xe3\x80\x80|\xef\xbb\xbf)+/",
    "_",
    $str
);

This accounts for and removes tabs, newlines, vertical tabs, formfeeds, carriage returns, spaces, and additionally from here:

nextline, non-breaking spaces, mongolian vowel separator, [en quad, em quad, en space, em space, three-per-em space, four-per-em space, six-per-em space, figure space, punctuation space, thin space, hair space, zero width space, zero width non-joiner, zero width joiner], line separator, paragraph separator, narrow no-break space, medium mathematical space, word joiner, ideographical space, and the zero width non-breaking space.

Many of these wreak havoc in xml files when exported from automated tools or sites which foul up text searches, recognition, and can be pasted invisibly into PHP source code which causes the parser to jump to next command (paragraph and line separators) which causes lines of code to be skipped resulting in intermittent, unexplained errors that we have begun referring to as "textually transmitted diseases"

[Its not safe to copy and paste from the web anymore. Use a character scanner to protect your code. lol]

This is an old post but the shortest answer is not listed here so I am adding it now

strtr($str,[' '=>'']);

Another common way to "skin this cat" would be to use explode and implode like this

implode('',explode(' ', $str));

$string = trim(preg_replace('/\s+/','',$string));

A simple way to remove spaces from the whole string is to use the explode function and print the whole string using a for loop.

 $text = $_POST['string'];
            $a=explode(" ", $text);
            $count=count($a);
            for($i=0;$i<$count; $i++){

                echo $a[$i];
            }

The \s regex argument is not compatible with UTF-8 multybyte strings.

This PHP RegEx is one I wrote to solve this using PCRE (Perl Compatible Regular Expressions) based arguments as a replacement for UTF-8 strings:

function remove_utf8_whitespace($string) { 
   return preg_replace('/\h+/u','',preg_replace('/\R+/u','',$string)); 
}

- Example Usage -

Before:

$string = " this is a test \n and another test\n\r\t ok! \n";

echo $string;

 this is a test
 and another test
         ok!

echo strlen($string); // result: 43

After:

$string = remove_utf8_whitespace($string);

echo $string;

thisisatestandanothertestok!

echo strlen($string); // result: 28

PCRE Argument Listing

Source: https://www.rexegg.com/regex-quickstart.html

Character   Legend  Example Sample Match
\t  Tab T\t\w{2}    T     ab
\r  Carriage return character   see below   
\n  Line feed character see below   
\r\n    Line separator on Windows   AB\r\nCD    AB
    CD
\N  Perl, PCRE (C, PHP, R…): one character that is not a line break \N+ ABC
\h  Perl, PCRE (C, PHP, R…), Java: one horizontal whitespace character: tab or Unicode space separator      
\H  One character that is not a horizontal whitespace       
\v  .NET, JavaScript, Python, Ruby: vertical tab        
\v  Perl, PCRE (C, PHP, R…), Java: one vertical whitespace character: line feed, carriage return, vertical tab, form feed, paragraph or line separator      
\V  Perl, PCRE (C, PHP, R…), Java: any character that is not a vertical whitespace      
\R  Perl, PCRE (C, PHP, R…), Java: one line break (carriage return + line feed pair, and all the characters matched by \v)      

There are some special types of whitespace in the form of tags. You need to use

$str=strip_tags($str);

to remove redundant tags, error tags, to get to a normal string first.

And use

$str=preg_replace('/\s+/', '', $str);

It's work for me.