Multiple ways to get file extension in PHP

This article mainly shares with you various methods of obtaining file extensions in PHP, hoping to help everyone.

Collected from the Internet, basically the following methods:

The 1st method:

function get_extension($file)
{
substr(strrchr($file, '.'), 1);
}

Note:

strrchr() function Finds the last occurrence of a string within another string and returns all characters from that position to the end of the string.

The substr() function returns a part of a string.

Method 2:

function get_extension($file)
{
return substr($file, strrpos($file, '.')+1);
}

Comments:

strrpos() function finds the last occurrence of a string in another string.

The substr() function returns a part of a string.

The third method:

function get_extension($file)
{
return end(explode('.', $file));
}

Comments:

explode() function breaks the string into an array.

end() function points the internal array pointer to the last element and returns the value of that element (if successful).

The 4th method:

function get_extension($file)
{
$info = pathinfo($file);
return $info['extension'];
}

Comments:

pathinfo() function returns the file path information in the form of an array.

The 5th method:

function get_extension($file)
{
return pathinfo($file, PATHINFO_EXTENSION);
}

Comments:

pathinfo() function returns the file path information in the form of an array.

After a quick look at the above methods, they all seem to work, especially methods 1 and 2, which I have been using before I didn’t know that pathinfo has a second parameter. But if you think about it carefully, the first four methods have various shortcomings. To obtain the file extension completely correctly, you must be able to handle the following three special situations.

No file extension

The path contains the character ., such as /home/test.d/test.txt

The path contains the character ., but the file does not extension name. For example, /home/test.d/test

is obvious: 1 and 2 cannot handle the third situation, and 3 cannot correctly handle the first and third situations. 4 is handled correctly, but when the extension is not present, a warning is issued. Only method 5 is the most correct method. By the way, take a look at the pathinfo method. The introduction on the official website is as follows:

$file_path = pathinfo('/www/htdocs/your_image.jpg');
echo "$file_path ['dirname']\n";
echo "$file_path ['basename']\n";
echo "$file_path ['extension']\n";
echo "$file_path ['filename']\n"; // only in PHP 5.2+

It will return an array containing up to four elements, but there will not always be four. For example, if there is no extension, there will be no extension element. That's why the warning will be found in the 4th method. But phpinfo also supports the second parameter. You can pass a constant to specify a certain part of the data to be returned:

PATHINFO_DIRNAME - 目录
PATHINFO_BASENAME - 文件名（含扩展名）
PATHINFO_EXTENSION - 扩展名
PATHINFO_FILENAME - 文件名（不含扩展名，PHP>5.2）

The values ​​​​of these four constants are 1, 2, 4, and 8 respectively. At first, I thought I could specify multiple ones through the OR operation:

pathinfo($file, PATHINFO_EXTENSION | PATHINFO_FILENAME);

Later I found out that this does not work, this will only return the smallest of several OR constants. That is, the smallest bit among the four flag bits is a constant.

Related recommendations:

How to use php to determine the file extension

php sample code to obtain the file extension

Summary of the example code for obtaining file extension in PHP

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