PHP file extension judgment and N methods to obtain file extension,

PHP file extension judgment and N methods to obtain file extension, _PHP tutorial

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Release： 2016-07-12 09:08:34

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N ways to determine the php file extension and get the file extension,

The following code is to determine the php file extension

<!DOCTYPE>
<html>
<head>
 <meta http-equiv="Content-type" content="text/html" charset="utf-8">
 <title>check file</title>
</head>
<body>
<b>文件扩展名验证</b>
<input type="text" name="int" value="文件.php" onblur="check(this)" id="int">
<input type="button" value="检测" onclick="check_value()">
<script>
 function check(obj){
  if(obj.value == "" || obj.value.length<3){
   alert("输入的长度不能小于3且不能为空!");
   obj.focus();
  }
 }
 function check_value(){
  var str = $("int").value;
  var repx = /\.(php|asp|jsp)$/i;
  var type = str.substring(str.lastIndexOf("."),str.length);
  if(type.match(repx) && str.lastIndexOf(".") != -1){
   alert("文件扩展名正确");
   $("int").focus();
  }else{
   alert("文件扩展名有误");
   $("int").focus();
  }
 }
 function $(obj){
  return document.getElementById(obj);
 }
</script>
</body>
</html>

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N ways to get file extension in PHP

Basically the following methods:

Method 1:

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

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Method 2:

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

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Method 3:

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

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Method 4:

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

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Method 5:

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

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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 characters., such as /home/test.d/test.txt

The path contains the character ., but the file has no extension. Such as /home/test.d/test

Obviously: 1 and 2 cannot handle the third situation, and 3 cannot handle the first and third situations correctly. 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+

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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, so the warning will be found in the fourth 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 - Directory
PATHINFO_BASENAME - file name (with extension)
PATHINFO_EXTENSION - extension
PATHINFO_FILENAME - filename (without extension, PHP>5.2)

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

pathinfo($file, PATHINFO_EXTENSION | PATHINFO_FILENAME);

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Later I found out that this doesn’t work. It will only return the smallest of several OR constants. That is, the smallest bit among the four flag bits is a constant of 1.

The above content introduces you to N ways to determine the PHP file extension and obtain the file extension. I hope you like it.