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Several ways to determine and obtain file extensions in PHP

墨辰丷

Jun 07, 2018 pm 01:49 PM

This article mainly introduces several methods for PHP to determine and obtain file extensions. Interested friends can refer to it. I hope it will be helpful to everyone.

The following code is to determine the file extension in PHP

<!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>

##N ways to get the file extension in PHP

Basically the following methods:

The 1st method:

function get_extension($file)
{
substr(strrchr($file, &#39;.&#39;), 1);
}

The 2nd method:

function get_extension($file)
{
return substr($file, strrpos($file, &#39;.&#39;)+1);
}

The 3rd method Method:

function get_extension($file)
{
return end(explode(&#39;.&#39;, $file));
}

The 4th method:

function get_extension($file)
{
$info = pathinfo($file);
return $info[&#39;extension&#39;];
}

The 5th method:

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

After a quick look at the above methods, they all seem to work, especially 1. 2 methods, 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:

$file_path = pathinfo(&#39;/www/htdocs/your_image.jpg&#39;);
echo "$file_path [&#39;dirname&#39;]\n";
echo "$file_path [&#39;basename&#39;]\n";
echo "$file_path [&#39;extension&#39;]\n";
echo "$file_path [&#39;filename&#39;]\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 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 (including extension)
PATHINFO_EXTENSION - extension
PATHINFO_FILENAME - file name (without extension) 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);

Later It is found 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 of 1.

Summary: The above is the entire content of this article, I hope it will be helpful to everyone's study.

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