php file_exists Check whether a file or directory exists_PHP tutorial

Under normal circumstances, it is no problem to use file_exists to check whether the file or directory exists, but please note that it will return false when the safe mode and directory do not have execution permissions.

Let’s first take a look at the usage of file_exists

The file_exists() function checks whether a file or directory exists.

Returns true if the specified file or directory exists, false otherwise.

Grammar
file_exists(path) parameter description
path is required. Specifies the path to be checked.
Example
echo file_exists("test.txt");
?>

Output:

1
According to this principle, I started working on the smarty template as follows

Introduction

I found a problem and share it with you today. Let me describe the whole process.

Question

The company has a framework written based on smarty. I am responsible for the upgrade of PHP. After the maintenance staff deployed the new environment, the testers came to me and reported frequent errors (error: file not found).
I traced the code and it turned out to be an error reported by smarty.

Error: The file reported here does not exist.

Thought process:

1. I originally thought that the file did not exist in the program, but it turned out that the file did exist. What happened?

2. Later, I guessed whether there was a problem with the PHP kernel. I looked through the relevant PHP kernel files and found no problem. As a result, I told the project manager about the entire process. ——The matter has not been resolved, so let’s just let it go. The upgrade is delayed for now.

I discovered this problem again today. My first reaction was whether the PHP version had been upgraded. I found out that it had not. ——Later, I set the entire directory to 777 and everything was fine (chmod 777 -R directory). I wonder if it is a problem with the file_exists() method.

So, I conducted relevant debugging and experiments.

Debugging code:

Directory:

Observe each permission: test does not have any permissions for www, while the execution file index.php has read and write execution permissions, and the included file test.txt has read and write permissions.

Run result:

The execution permission of the directory affects file_exists()

1. Give test the maximum permission - 755

Since it is successful, it means that the file_exists() function is restricted by directory permissions.

So what kind of directory permissions affect file_exists()?

I did a few experiments: 1. In any superior directory of the file, if it only has write permission, the file does not exist;

2. Any parent directory of the file will report that the file does not exist even if it only has read permission;

3. When all upper-level directories have execution permissions, the reported file exists and everything is normal.

The result shows that file_exists() recursively determines whether each directory has execution permission when determining whether a file exists.

Modify the file path to a relative path and get the same result.

Summary

There is no mention in the PHP manual that file_exists will be affected by the execution permission of the directory. Today, I would like to inform developers who also have this problem through this article. Just take this as a warning.

Additional information

Thank you all for your comments, they are very useful. After everyone's opinions, I checked the manual again. Indeed, if the directory does not have execution permissions, the php-fpm application process cannot go to this directory to search for files. Of course, it will be considered that the file does not exist (actually it is considered that there is no executable directory). does not exist).
You can consider the contents of the manual together, mainly about execution permissions. I won’t go into details about read and write permissions here (generally they are easy to understand).

Obviously in the manual, there are clear instructions on the execution permissions of the directory. Execute permission on a directory means having the right to be searched. ​

Finally, I found a Warning
on the php official website If the file cannot be accessed due to safe mode restrictions, this function returns FALSE. However, if the file is in the directory specified by safe_mode_include_dir, it can still be included using include. Everyone can also pay attention to this.

http://www.bkjia.com/PHPjc/632216.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/632216.htmlTechArticleUnder normal circumstances, we use file_exists to check whether a file or directory exists. There is no problem, but one thing to note is When safe mode and the directory do not have execution permission, f...