PHP trim(): Remove Whitespace from a String

trim($string) returns the string with whitespace removed from the start and the end: spaces, tabs, newlines, carriage returns, NUL bytes and vertical tabs. ltrim() removes it only from the start and rtrim() only from the end. Spaces in the middle are kept.

<?php
$input = "   Ada Lovelace \n";

var_dump(trim($input));
var_dump(ltrim($input));
var_dump(rtrim($input));

The var_dump() output shows the length of each result, which makes the removed characters visible. Trimming is the first thing to do with most values from a form (passwords are the exception, see the end of the page): a user who types ada@example.com with a trailing space should still be able to log in.

Syntax

trim(string $string, string $characters = " \n\r\t\v\0"): string
ltrim(string $string, string $characters = " \n\r\t\v\0"): string
rtrim(string $string, string $characters = " \n\r\t\v\0"): string

trim() returns a new string; it does not change the variable you pass in.

Trim specific characters

The second argument replaces the default list. Every character in it is removed from the ends, in any order and any number of times. .. defines a range, so 'a..z' means every lowercase letter.

<?php
echo trim('***Sale***', '*'), "\n";
echo rtrim('red, green, blue, ', ', '), "\n";   // remove the trailing ", "
echo ltrim('000123', '0'), "\n";                // leading zeros
echo trim('/blog/post/', '/'), "\n";
echo trim('abc123xyz', 'a..z'), "\n";           // every lowercase letter

To also keep removing normal whitespace, include it in the list: trim($s, " \n\r\t\v\0/").

The second argument is a set of characters, not a string

trim() does not remove a word or suffix. It removes any of the characters you list, from both ends, until it reaches one that is not in the list. That surprises people who try to strip a file extension:

<?php
// Looks like "remove .php", but removes the characters . p h from both ends
var_dump(trim('hello.php', '.php'));

// Remove a suffix: check it, then cut it off
$file = 'hello.php';
if (str_ends_with($file, '.php')) {
    $file = substr($file, 0, -strlen('.php'));
}
var_dump($file);

The first line removes the h at the start too, because h is in the set. To remove a fixed prefix or suffix, use str_starts_with() or str_ends_with() with substr(), or str_replace() if the text cannot appear anywhere else.

Trim the full-width space (Japanese input)

Japanese keyboards often produce the ideographic space 　 (U+3000), for example around a name typed into a form. It is not in trim's default list, and listing it in the second argument is a trap: trim() works byte by byte, the space is the 3 bytes E3 80 80, and E3 is also the first byte of every hiragana and katakana character, so a name that starts with one loses that character's first byte. Use a regular expression with the u modifier:

<?php
$name = '　さとう 花子　 ';

var_dump(trim($name));   // the full-width spaces stay

// Listing the space as a character breaks さ: the result is not valid UTF-8
var_dump(mb_check_encoding(trim($name, '　'), 'UTF-8'));

function mbTrim(string $s): string
{
    return preg_replace('/\A\s+|\s+\z/u', '', $s);
}

var_dump(mbTrim($name));

\A and \z anchor to the start and end of the string. With the u modifier, \s matches every Unicode space: the ASCII whitespace, the full-width space and the non-breaking space (U+00A0) that copy and paste from web pages often brings. Without u, \s matches ASCII whitespace only and the full-width space stays. PHP 8.4 adds mb_trim(), mb_ltrim() and mb_rtrim() for this; on PHP 8.3 and earlier the regex is the way.

Trim every value in an array

array_map('trim', $array) trims each value and keeps the keys. A typical case is a comma separated list from a text field, split with explode():

<?php
$tags = explode(',', ' php , mysql,  laravel ,');

$tags = array_map('trim', $tags);
$tags = array_filter($tags, fn($t) => $t !== '');

print_r(array_values($tags));

// An associative array of form fields keeps its keys
$form = ['name' => '  Ada ', 'email' => " ada@example.com\n"];
print_r(array_map('trim', $form));

Trim a form value before validating it

Trim first, then check for an empty string. A field that contains only spaces is then rejected as empty. Run this block, type a name with spaces around it into the form and press Send: the same script runs again with $_POST filled in.

<?php
$raw = $_POST['name'] ?? '';
$name = trim($raw);
$error = '';

if (($_SERVER['REQUEST_METHOD'] ?? 'GET') === 'POST' && $name === '') {
    $error = 'Please enter your name.';
}
?>
<form method="post">
  <input name="name" value="<?= htmlspecialchars($raw) ?>">
  <button>Send</button>
</form>
<?php if ($error !== ''): ?>
  <p style="color: #c00"><?= $error ?></p>
<?php elseif ($name !== ''): ?>
  <p>Sent "<?= htmlspecialchars($raw) ?>", saved "<?= htmlspecialchars($name) ?>" (<?= strlen($raw) ?> bytes became <?= strlen($name) ?>)</p>
<?php endif; ?>

Do not trim passwords: a space at the end of a password is part of it.