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PsySH provides several magic variables that give you access to previous results, exceptions, output, and more.

​
Core Magic Variables

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$_ - Last Return Value

The $_ variable holds the return value of the most recently executed statement: 
>>> 2 + 2
=> 4
>>> $_
=> 4
>>> $_ * 10
=> 40
This is incredibly useful for chaining operations without assigning temporary variables.

​
$_e - Last Exception

The $_e variable contains the most recent exception or error: 
>>> throw new RuntimeException('Oops!')

  RuntimeException with message 'Oops!'

>>> $_e
=> RuntimeException {
     +message: "Oops!",
     +code: 0,
     +file: "eval()'d code",
     +line: 1,
     ...
   }
>>> $_e->getMessage()
=> "Oops!"
>>> $_e->getTraceAsString()
$_e is only available after an exception has been thrown. Accessing it before will result in an error.

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$__out - Last Standard Output

The $__out variable captures the output from the most recent statement: 
>>> echo "Hello, World!\n"
Hello, World!
>>> $__out
=> "Hello, World!\n"
>>> echo "Debug: " . $__out
Debug: Hello, World!
$__out is updated whenever code prints to standard output using echo, print, var_dump(), etc. It captures all output from a single statement execution.

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Context Variables

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$this - Bound Object

When debugging within an object context, $this refers to the bound object: 
class User {
    private $name = 'Alice';
    
    public function debug() {
        \Psy\debug(get_defined_vars(), $this);
    }
}

$user = new User();
$user->debug();
// Inside PsySH:
>>> $this->name
=> "Alice"
$this is only available when PsySH is started with a bound object context. See the Debugging guide for more details.

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Command Scope Variables

These variables provide metadata about the current execution context, similar to PHP’s magic constants:

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$__class

The current class name: 
>>> class MyClass {}
>>> $__class
=> "MyClass"

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$__namespace

The current namespace: 
>>> namespace App\Services;
>>> $__namespace
=> "App\\Services"

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$__file

The current file path: 
>>> $__file
=> "/path/to/current/file.php"

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$__line

The current line number: 
>>> $__line
=> 42

​
$__dir

The directory of the current file: 
>>> $__dir
=> "/path/to/current"

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$__function

The current function name: 
>>> function myFunction() { \Psy\debug(); }
>>> myFunction();
// Inside PsySH:
>>> $__function
=> "myFunction"

​
$__method

The current method name: 
>>> class Test {
...     public function myMethod() { \Psy\debug(); }
... }
>>> (new Test())->myMethod();
// Inside PsySH:
>>> $__method
=> "Test::myMethod"
Command scope variables are only set when using certain commands like whereami or when debugging from specific contexts. They may not always be available.

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Practical Examples

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Chaining Operations

Use $_ to build up complex operations: 
>>> json_decode('{"users": [{"name": "Alice"}, {"name": "Bob"}]}')
=> {
     +users: [
       {
         +name: "Alice",
       },
       {
         +name: "Bob",
       },
     ],
   }
>>> $_->users
=> [
     {
       +name: "Alice",
     },
     {
       +name: "Bob",
     },
   ]
>>> $_[0]->name
=> "Alice"

​
Debugging Exceptions

Examine exceptions in detail: 
>>> $data = [];
>>> $data['missing']['key']

  Warning: Undefined array key "missing"

>>> $_e
=> ErrorException {
     +message: "Undefined array key \"missing\"",
     +severity: E_WARNING,
     ...
   }
>>> $_e->getSeverity() === E_WARNING
=> true

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Capturing Output for Testing

Use $__out to verify output: 
>>> function greet($name) {
...     echo "Hello, {$name}!";
... }
>>> greet('World')
Hello, World!
>>> assert($__out === 'Hello, World!')
=> true

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Variable Scope

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Setting Variables

Variables you define persist throughout the session: 
>>> $config = ['debug' => true, 'env' => 'dev']
=> [
     "debug" => true,
     "env" => "dev",
   ]
>>> $config['debug']
=> true

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Viewing All Variables

Use the ls command to see all defined variables: 
>>> ls -v
Variables:
  $_       int             4
  $config  array           ['debug' => true, 'env' => 'dev']
  $name    string          "World"

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Protected Variables

Magic variables cannot be overwritten: 
>>> $_ = 'my value'  // This sets a regular variable
>>> 2 + 2
=> 4
>>> $_  // The magic variable takes precedence
=> 4
Magic variables are read-only in the sense that they’re automatically updated by PsySH. Any explicit assignments are ignored in favor of the automatic values.

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Working with History

Combine magic variables with history replay: 
>>> $numbers = [1, 2, 3, 4, 5]
>>> array_sum($_)
=> 15
>>> $total = $_
>>> $average = $total / count($numbers)
=> 3
See the History Management guide for more details on using history.

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Source Code Reference

Magic variables are managed in the Context class:
  • $_, $_e, $__out - Defined in src/Context.php:22-28
  • Return values set via setReturnValue() - src/Context.php:148
  • Exceptions set via setLastException() - src/Context.php:168
  • Output captured via setLastStdout() - src/Context.php:192

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