Definition and Usage

PHP Version
4+

The trim() function removes whitespace or characters specified by a parameter from both ends of a string.

This function is commonly used to remove unexpected whitespace from the beginning and end of user input strings.

Basic Example

PHP 
/* Remove whitespace from both ends of a string */
$string = '   hello world   ';
$trimmed = trim($string);
var_dump($trimmed); // Output: string(11) "hello world"

/* Remove characters specified by a parameter */
$string = 'hello world';
$trimmed = trim($string, 'he');
var_dump($trimmed); // Output: string(9) "llo world"

/*
 * Caution: trim() does not properly handle multibyte characters,
 * such as Japanese characters, which may cause encoding issues.
 */
$string = 'ようこそ';
$trimmed = trim($string, 'よう');
var_dump($trimmed); // Output: string(4) "�そ"

Syntax

PHP 
trim(string $string, string $characters = " \n\r\t\v\x00"): string

Parameters

Description of the trim() function parameters
$string Required. The string from which characters will be removed.
$characters Optional. Specifies which characters to remove. If omitted, the following whitespace characters are removed by default:
  • " ": Space – the standard space character entered when you press the Space key.
  • \n: Newline – the line break character inserted when you press the Enter key.
  • \r: Carriage return – a control character that moves the cursor to the beginning of the line. Historically, this was used to return the print head to the start position on printers.
  • \t: Tab – the horizontal tab character inserted when you press the Tab key.
  • \v: Vertical tab – a control character that moves the output position vertically.
  • \x00: NUL-byte – the null character often used to mark the end of a string.

The trim() function does not support multibyte characters, such as Japanese, when removing characters specified by the parameter, so use caution.

Return Values

The trim() function returns the string after removing whitespace or characters specified by the parameter from both ends of the string. Note that it does not support multibyte characters, such as Japanese, when removing characters specified by the parameter, so use caution.

PHP 
 * Caution: trim() does not properly handle multibyte characters,
 * such as Japanese, which may cause garbled output.
 */
$string = 'ようこそ';
$trimmed = trim($string, 'よう');
var_dump($trimmed); // Output: string(4) "�そ"

In such cases, you can handle multibyte characters using functions like preg_replace(), as shown below:

Additional Explanation
The preg_replace() function uses regular expressions to search for patterns within a string and replace them with other text.

PHP 
$original_string = 'ようこそ。はじめまして！';
$trim_string = preg_replace('/^よう/u', '', $original_string);

var_dump($trim_string); // Output: string(30) "こそ。はじめまして！"

Due to the inconvenience of trim() not supporting multibyte characters for the parameter, this function is mainly used to remove whitespace characters rather than other specified characters.

Practical Examples

The trim() function is primarily used to filter out (remove) whitespace characters—including spaces, tabs, and newlines—from the beginning and end of a string. This is a common task when handling user input or external data, helping to clean up strings and maintain data consistency.

Here are some practical examples:

User Input Handling

PHP 
$username = trim($_POST['username']);
$password = trim($_POST['password']);

You can process user-provided input by removing extra spaces from the username and password fields.

Using in Database Queries

PHP 
$input = '   some value   ';
$cleaned_input = trim($input);
$query = "SELECT * FROM table WHERE column = '$cleaned_input'";

When constructing database queries, trim() can be used to preprocess input values.

Text File Processing

PHP 
$lines = file('example.txt', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
$cleaned_lines = array_map(function($line) { return trim($line); }, $lines);

Additional Explanation
The array_map() function applies a given callback function to each element of an array and returns a new array.

This removes leading and trailing whitespace from each line in a text file and stores the cleaned lines in an array. Each line is processed with trim() before being added to the $cleaned_lines array.

References

See also