String Functions
PHP Manual

substr

Return part of a string

Description

string substr(string $string, int $offset, intnull $length = null)

Returns the portion of string specified by the offset and length parameters.

Parameters

string

The input string.

offset

If offset is non-negative, the returned string will start at the offset'th position in string, counting from zero. For instance, in the string 'abcdef', the character at position 0 is 'a', the character at position 2 is 'c', and so forth.

If offset is negative, the returned string will start at the offset'th character from the end of string.

If string is less than offset characters long, an empty string will be returned.

Example #1 Using a negative offset

<?php
$rest = substr("abcdef", -1);    // returns "f"
$rest = substr("abcdef", -2);    // returns "ef"
$rest = substr("abcdef", -3, 1); // returns "d"
?>

length

If length is given and is positive, the string returned will contain at most length characters beginning from offset (depending on the length of string).

If length is given and is negative, then that many characters will be omitted from the end of string (after the start position has been calculated when a offset is negative). If offset denotes the position of this truncation or beyond, an empty string will be returned.

If length is given and is 0, an empty string will be returned.

If length is omitted or null, the substring starting from offset until the end of the string will be returned.

Example #2 Using a negative length

<?php
$rest = substr("abcdef", 0, -1);  // returns "abcde"
$rest = substr("abcdef", 2, -1);  // returns "cde"
$rest = substr("abcdef", 4, -4);  // returns ""; prior to PHP 8.0.0, false was returned
$rest = substr("abcdef", -3, -1); // returns "de"
?>

Return Values

Returns the extracted part of string, or an empty string.

Changelog

Version Description
8.0.0 length is nullable now. When length is explicitly set to null, the function returns a substring finishing at the end of the string, when it previously returned an empty string.
8.0.0 The function returns an empty string where it previously returned false.

Examples

Example #3 Basic substr usage

<?php
echo substr('abcdef', 1);     // bcdef
echo substr("abcdef", 1, null); // bcdef; prior to PHP 8.0.0, empty string was returned
echo substr('abcdef', 1, 3);  // bcd
echo substr('abcdef', 0, 4);  // abcd
echo substr('abcdef', 0, 8);  // abcdef
echo substr('abcdef', -1, 1); // f

// Accessing single characters in a string
// can also be achieved using "square brackets"
$string = 'abcdef';
echo $string[0];                 // a
echo $string[3];                 // d
echo $string[strlen($string)-1]; // f

?>

Example #4 substr casting behaviour

<?php
class apple {
    public function __toString() {
        return "green";
    }
}

echo "1) ".var_export(substr("pear", 0, 2), true).PHP_EOL;
echo "2) ".var_export(substr(54321, 0, 2), true).PHP_EOL;
echo "3) ".var_export(substr(new apple(), 0, 2), true).PHP_EOL;
echo "4) ".var_export(substr(true, 0, 1), true).PHP_EOL;
echo "5) ".var_export(substr(false, 0, 1), true).PHP_EOL;
echo "6) ".var_export(substr("", 0, 1), true).PHP_EOL;
echo "7) ".var_export(substr(1.2e3, 0, 4), true).PHP_EOL;
?>

The above example will output:

1) 'pe'
2) '54'
3) 'gr'
4) '1'
5) ''
6) ''
7) '1200'

Example #5 Invalid Character Range

If an invalid character range is requested, substr returns an empty string as of PHP 8.0.0; previously, false was returned instead. 

<?php
var_dump(substr('a', 2));
?>

Output of the above example in PHP 8:

string(0) ""

Output of the above example in PHP 7:

bool(false)

See Also