How to check if data is empty or whitespace only in PHP

Question

I have an input field that needs a username. The scenario is, how can i prevent user from providing whitespace or whitespaces in the that field? I already added required in the input field so i can prevent user from leaving it blank.

<input type="text" name="username" required>

but what if the user puts whitespace or as many whitespace as he can, is there any possible way i can detect this and throw error to the user?

in my php file i already have

if(empty($_POST['username'])){
echo "Username should not be empty!";
}

but this will fail because of the whitespaces the users put in the input field.

Levina

empty() is nearly useless for such things. empty(0) is true. try strlen()==0 instead. – Xylol

Answer 1

You could do like this.

if(isset($_POST['username']))
{
    if(strlen(trim($_POST['username'])) == 0){
        echo "Username should not be empty!";
    }
}

In the modern PHP it can be shorter

if (!trim($_POST['username'] ?? '')) {
    echo "Username should not be empty!";
}

or, if you need to assign $_POST['username'] to a variable

$username = trim($_POST['username'] ?? '');
if(!$username) {
    echo "Username should not be empty!";
}

Dianoia

In this case the call to empty() is unnecessary, the strlen(trim()) calls are enough. You should either do empty(trim()) or strlen(trim()) – Harrisonharrod

@RainFromHeaven, Yeah changed it. – Dianoia

Shouldn't it be ==0 or am I missing something? How would the length of the string ever be less than 0? – Okhotsk

@Danny, Yeah or <= , Fail safe ;) – Dianoia

I guess your right.. i need <= . = is not working for me.. i should accept this now :) – Levina

@Levina you need 2 ='s – Okhotsk

Answer 2

You can use trim and strlen php functions

Burgett

let me try trim.. but strlen? i don't think so .. this will just count the number of characters including the whitespace. – Levina

@Levina strlen(trim($_POST['foo'])) – Harrisonharrod

oh sorry if i misunderstood your answer. i think your idea is the same with @Shankar .. i never thought it is possible to combine the two. sorry. – Levina

shortest way is if(! trim($_POST['username']) ) – Gamelan

Answer 3

Try This....

if( trim($_POST['username']) == ""){
     echo "Username should not be empty!";
}

Cost

will raise an error if $_POST['username'] is not set – Rajewski

Answer 4

I can see this is quite old question but is still in the top results when searching for a way to check if string contains only whitespace characters.

PHP trim method (as well as other methods like ctype_space) doesn't actually remove all possible whitespace characters. Trim removes only:

" " (ASCII 32 (0x20)), an ordinary space.
"\t" (ASCII 9 (0x09)), a tab.
"\n" (ASCII 10 (0x0A)), a new line (line feed).
"\r" (ASCII 13 (0x0D)), a carriage return.
"\0" (ASCII 0 (0x00)), the NUL-byte.
"\v" (ASCII 11 (0x0B)), a vertical tab.

(all copied from https://www.php.net/manual/en/function.trim.php)

And wiki specifies about 32 whitespace chars (6 from which are only related to whitespace but marked as not-whitespace, so the table is separate into two groups, you decide if you need the second group)

Then to check if string contains only whitespace:

// BE AWARE that I'm assuming that text is in UTF-8 (which will be probably true in most cases) 
/**
 * Find the end of the UTF-8 char
 * https://mcmap.net/q/281060/-how-to-iterate-utf-8-string-in-php
 * @param  string $string     UTF-8 string
 * @param  int    $pointer    Start of the character (byte)
 * @param  int    $nextLetter Reference to save where next character starts
 * @return string             Whole letter
 */
function get(string $string, int $pointer, int &$nextLetter): string|bool
{
    if (!isset($string[$pointer])) {
        return false;
    }

    $char = ord($string[$pointer]);

    if ($char < 128) {
        $nextLetter = $pointer + 1;
        return $string[$pointer];
    }

    if ($char < 224) {
        $bytes = 2;
    } elseif ($char < 240) {
        $bytes = 3;
    } else {
        $bytes = 4;
    }
    $str = substr($string, $pointer, $bytes);
    $nextLetter = $pointer + $bytes;
    return $str;
}


function isWhitespace(string $string): bool
{
    if (strlen($string) == 0) {
        return false;
    }

    // https://en.wikipedia.org/wiki/Whitespace_character
    $table = [
        // Unicode characters with property White_Space=yes
        "\u{0009}" => true, "\u{000A}" => true, "\u{000B}" => true, "\u{000C}" => true,
        "\u{000D}" => true, "\u{0020}" => true, "\u{0085}" => true, "\u{00A0}" => true,
        "\u{1680}" => true, "\u{2000}" => true, "\u{2001}" => true, "\u{2002}" => true,
        "\u{2003}" => true, "\u{2004}" => true, "\u{2005}" => true, "\u{2006}" => true,
        "\u{2007}" => true, "\u{2008}" => true, "\u{2009}" => true, "\u{200A}" => true,
        "\u{2028}" => true, "\u{2029}" => true, "\u{202F}" => true, "\u{205F}" => true,
        "\u{3000}" => true,
        // Related Unicode characters with property White_Space=no
        "\u{180E}" => true, "\u{200B}" => true, "\u{200C}" => true, "\u{200D}" => true,
        "\u{2060}" => true, "\u{FEFF}" => true,
    ];
    $nextLetter = $i = 0;

    // Iterate over the string and cut it into proper UTF-8 letters
    // We have to do this to have actual letters and not letters chunked into bytes
    // as they will be saved in multiple spaces, so spliting text by 1 with substr
    // will only return in trash characters if we encounter something that has length
    // bigger then 1 byte
    //
    // If you have mbstring extension installed you might want to use mb_substr but this
    // will be a lot slower as for each cut it will iterate over the string (again from the start)
    // to cut it into properly sized chunks. Have a read:
    // https://www.php.net/manual/en/function.mb-substr.php - note from `qbolec at gmail dot com`
    while (($letter = get($string, $i, $nextLetter)) !== false) {
        // Quick exit if any char is not whitespace to prevent additional loops
        if (!isset($table[$letter])) {
            return false;
        }
        $i = $nextLetter;
    }

    return true;
}

Usage:

isWhitespace("\t\n\r");  // true
isWhitespace("\td\n\r"); // false
isWhitespace("");        // false
// This one is "\u{2003}\u{2000}\u{2009}" (em space, en quad and thin space) but in UTF-8
isWhitespace("   ");     // true

To check if something is empty you can use empty method:

if (empty($string)) {
    // Is empty!
}

If you don't want to separate string into proper letters manually in each project (like me) you might want to use my library - https://github.com/Mortimer333/Content

Ucayali

Answer 5

I think str_replace() is all you want. Or you could some javascript to prevent whitespace from being entered into the input field.

<?php
$s = str_replace(' ', '', $_POST['username']);
?>

If you're going to use trim(), don't forget about rtrim()

Speight

will remove spaces from the string – Rajewski

Answer 6

u can use $.trim() jquery function before to submit form.

var nowhitespace = $.trim($("#input").val());

Yasukoyataghan

Answer 7

Ensure there's a space between the inverted commas:

if(empty($_POST['firstname']) || $_POST['Firstname'] = " "){
  echo "cannot be empty";
}

Luigi