Tuesday, May 21, 2013

Say Goodbye to PHP shell_exec() and PHP exec()

Dealing with the shell in PHP can be a pain. If you are executing anything more complicated than a no argument command with a one line string result, things start getting complicated.

To get started, if you want to check the return status of your commands, you need to pass a reference parameter to exec()! Ok, so it's not returning the command exit status, well then you might expect that it returns the command's output instead? Nope; the return value of exec()is actually the last line from the command's output. If you want to get the full output of the command, then you're looking at yet another reference parameter. And wait, which order do those references parameters go?

After you've got your parameters sorted out, what about escaping arguments for security and accuracy? For that, you're left manually using PHP's other global functions.

Alright, so now you've got a safe, accurate command. How do you know it works? You might want to test it, right? Well, if you want to test any of your code that uses exec(), you're looking at a rough road ahead because PHPUnit has no facility to let you make assertions against parameters passed by reference. Furthermore, if you have more than one call to exec, then you really have no way to stub results out of the box because you can't differentiate between calls to exec. I previously blogged about one approach I've taken to solving this -- http://asheepapart.blogspot.com/2012/10/testing-shell-methods-with-phpunit.htmlMockShell works alright, but it doesn't help us with escaping the command for security or accuracy.

Enter the Bart Command class. Command is a simple class that acts as a facade over a single shell command. It takes a variable number of arguments to its constructor, representing arguments to the shelled command. The first constructor arg is reserved for the actual command itself. Each shell argument is escaped and then substituted for placeholders in the shell command.

A command can be passed around and executed on demand. The results are returned as a full string or an array of each line. If the command fails, a custom exception of type is CommandException thrown.

We're using Command extensively in our internal code bases with a lot of success. Currently, you can see it used in a few places in the Git class.

I also created the gist below,


Testing is easy. There isn't any pass-by-reference magic, you can just apply all your standard testing know-how. You can use Diesel to inject your stub into your system under test. You can also mock the results of the shorthand Shell->command() method.

1 comment:

  1. Nice and good article.. it is very useful for me to learn and understand easily.. thanks for sharing your valuable information and time.. please keep updating.more 
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