PHP substr() Function: Usage, Parameters, and Examples

substr() returns a portion of a string.

Signature: string substr(string $string, int $start[, int $length])

Explanation: Returns the substring of $string defined by $start and $length . If $start is non‑negative, counting begins at that offset (0‑based). If negative, counting starts from the end of the string. If $length is omitted, the substring extends to the end of the string.

Parameter details:

string – the input string (must contain at least one character).

start – position where extraction begins. Positive values count from the start; negative values count backward from the end. If the string length is less than start , FALSE is returned.

length – optional. Positive values limit the number of characters returned. Negative values cause characters at the end of the string to be omitted. Zero, FALSE , or NULL results in an empty string. If omitted, extraction continues to the string's end.

Example 1:

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

Example 2:

<?php
$rest = substr("abcdef", 0, 2); // returns "ab"
$rest = substr("abcdef", 2, 3); // returns "cde"
$rest = substr("abcdef", 4, -4); // returns "" (empty string)
?>

Example 3 (character access):

<?php
$string = "abcdef";
echo $string[0]; // a
echo $string[3]; // d
echo $string[strlen($string) - 1]; // f
?>

Example 4 (object to string conversion and var_export):

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

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

The output of the above calls demonstrates how substr() behaves with strings, numbers, objects, booleans, empty strings, and scientific notation values.