PHP substr() Function: Syntax, Parameters, Return Values, and Practical Usage Examples

substr() Function Syntax

The substr() function is a commonly used PHP function for extracting a portion of a string based on a specified start position and length.

substr(string $string, int $start, int $length = null): string|false

Parameter Description

$string

: The string to be sliced. $start: The start position; if negative, counting starts from the end of the string. $length: Optional length of the slice; if omitted, the function extracts from the start position to the end of the string.

Return Value

On success, returns the extracted substring.

On failure, returns false.

Usage of substr()

1. Extract a Part of a String

Example of extracting the word "World" from a string:

$str = "Hello, World!";<br/>$substring = substr($str, 7, 5);<br/>echo $substring; // Output: World

In this example, the start position is 7 (the 8th character) and the length is 5, resulting in the substring "World".

2. Extract and Replace a Substring

Extract a substring and replace it with another value, such as changing "World" to "PHP":

$str = "Hello, World!";<br/>$substring = substr($str, 7, 5);<br/>$newStr = str_replace($substring, "PHP", $str);<br/>echo $newStr; // Output: Hello, PHP!

The code first extracts "World" using substr(), then replaces it with "PHP" using str_replace().

3. Extract and Change Case

Extract a substring and convert it to uppercase (or lowercase) before reinserting it:

$str = "Hello, World!";<br/>$substring = substr($str, 7, 5);<br/>$uppercase = strtoupper($substring);<br/>$newStr = str_replace($substring, $uppercase, $str);<br/>echo $newStr; // Output: Hello, WORLD!

This example extracts "World", converts it to uppercase with strtoupper(), and then replaces the original substring using str_replace().

Summary

The substr() function is a versatile PHP tool for string manipulation, allowing developers to extract, replace, or change the case of substrings based on start position and length, with support for negative indices and optional length parameters.

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