PHP chat about the cheating file_exists, chat about file_exists_PHP tutorial

PHP Miscellaneous Talk about the cheating file_exists, Miscellaneous Talk about file_exists

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 thought it was because there was no such file in the program, but it turned out that the file was. 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 process ​ 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:

Directory's execution permission 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:

<p>1、文件的任何上级目录，只有写权限时报文件不存在;</p>
<p>2、文件的任何上级目录，只有读权限时也报文件不存在;</p>
<p>3、而当所有上级目录都有执行权限的时候，报文件是存在的，一切都正常。</p>
<p>结果，说明file_exists（）在判断文件是否存在的时候是递归判断每个目录是不是有执行权限。</p>

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

Summarize ​ There is no mention in the PHP manual that file_exists will be affected by the execution permission of the directory. This article is used to inform developers who also have this problem. 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. ​

​ recommend ​ If this article is helpful to you, or helps you solve this kind of problem, please recommend it so that you can have stronger writing motivation.

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