How to Check the Executability of Symlink Files Using is_executable in PHP

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<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// This is a prelude PHP code example unrelated to the article content</span></span><span>
</span><span><span class="hljs-variable">$timestamp</span></span><span> = </span><span><span class="hljs-title function_ invoke__">time</span></span><span>();
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Current timestamp: <span class="hljs-subst">$timestamp</span></span></span><span>\n";
</span><span><span class="hljs-meta">?&gt;</span></span><span>
<p><hr></p>
<p></span><span><span class="hljs-comment"># How to check the executability of symlink files using <code>is_executable

This function returns true or false, depending on whether the current user has execution rights for the file.

2. Symlinks and Executability Checks

When checking a symlink, is_executable() does not check the symlink’s own permissions but the executability of the file it points to. For example:

<span><span><span class="hljs-variable">$symlink</span></span><span> = </span><span><span class="hljs-string">&#039;/path/to/symlink&#039;</span></span><span>;
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">is_executable</span></span><span>(</span><span><span class="hljs-variable">$symlink</span></span><span>)) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"The file pointed to by symlink <span class="hljs-subst">$symlink</span> is executable"</span></span><span>;
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"The file pointed to by symlink <span class="hljs-subst">$symlink</span> is not executable"</span></span><span>;
}
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Key points to note:

• If the target file exists and is executable, it returns true.

• If the target file does not exist, it returns false.

• If the symlink does not point to a valid file, it returns false.

3. Using readlink() to Get the Symlink Target

Sometimes you may want to explicitly know the path a symlink points to. You can use readlink():

<span><span><span class="hljs-variable">$symlink</span></span><span> = </span><span><span class="hljs-string">&#039;/path/to/symlink&#039;</span></span><span>;
</span><span><span class="hljs-variable">$target</span></span><span> = </span><span><span class="hljs-title function_ invoke__">readlink</span></span><span>(</span><span><span class="hljs-variable">$symlink</span></span><span>);

</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$target</span></span><span> !== </span><span><span class="hljs-literal">false</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Symlink points to: <span class="hljs-subst">$target</span></span></span><span>\n";
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">is_executable</span></span><span>(</span><span><span class="hljs-variable">$target</span></span><span>)) {
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Target file is executable"</span></span><span>;
    } </span><span><span class="hljs-keyword">else</span></span><span> {
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Target file is not executable"</span></span><span>;
    }
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"This is not a valid symlink"</span></span><span>;
}
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This way, you can clearly know that executability applies to the target file, not the symlink itself.

4. Precautions

1. Cross-platform differences: Windows has limited symlink support, so is_executable may behave differently than on Linux or macOS.

2. Permission issues: Even if the file has executable permissions, if the PHP script's user lacks access, it will return false.

3. Security: When handling user-uploaded or dynamically generated symlinks, be cautious of symlink attacks.

Conclusion

• is_executable() can check whether a file is executable, including the targets of symlinks.

• For symlinks, the function checks the permissions of the target file, not the link itself.

• Using readlink() to clarify the target path improves code readability and security.

By following these methods, you can reliably determine the executability of symlink files in PHP, managing file permissions safely and effectively.

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• Related Tags:

  is_executable