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PsySH is a runtime developer console, interactive debugger and REPL (Read-Eval-Print Loop) for PHP. This guide covers the basics of using the REPL.

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Starting the REPL

1

Launch PsySH

Run the PsySH command to start an interactive session:
psysh
You’ll see the PsySH prompt:
Psy Shell v0.12.20 (PHP 8.3.0 — cli) by Justin Hileman
>>>
2

Execute PHP Code

Type any PHP expression at the prompt:
>>> $name = 'World'
=> "World"
>>> echo "Hello, {$name}!"
Hello, World!
The => prefix shows the return value of your expression.
3

Use Commands

PsySH includes built-in commands prefixed with a colon or period:
>>> help
>>> ls
>>> doc array_map

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Interactive Features

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Multi-line Input

PsySH automatically detects incomplete statements and prompts for more input: 
>>> function greet($name) {
...   return "Hello, {$name}!";
... }
=> null
>>> greet('Alice')
=> "Hello, Alice!"
Use a backslash \ at the end of a line to continue input on the next line, even if the statement is complete.

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Code Buffer Management

The code buffer holds your multi-line input as you type: 
>>> $items = [
...   'apple',
...   'banana',
...   'cherry'
... ];
  • clear - Clear the code buffer
  • buffer - Show the current code buffer contents
  • Press Ctrl+D while in an incomplete expression to clear the buffer

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Loading Files

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Include Files at Startup

Load PHP files when starting PsySH: 
psysh config.php helpers.php

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Include Files During Session

Use standard PHP include statements: 
>>> require 'vendor/autoload.php'
>>> include 'my-functions.php'

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Working with Output

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Return Values

Every expression shows its return value: 
>>> 2 + 2
=> 4
>>> strlen('hello')
=> 5
>>> [1, 2, 3]
=> [
     1,
     2,
     3,
   ]

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Standard Output

Printed output appears without the => prefix: 
>>> echo "Debug info\n"
Debug info
>>> var_dump(['a' => 1, 'b' => 2])
array(2) {
  ["a"]=>
  int(1)
  ["b"]=>
  int(2)
}
Lines ending without a newline show a special indicator (⏎) to make it clear where output ends.

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Exiting the REPL

Use the exit command:
>>> exit

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Error Handling

PsySH catches exceptions and displays them with helpful formatting: 
>>> throw new Exception('Something went wrong')

  Exception with message 'Something went wrong'

>>> 1 / 0

  Warning: Division by zero
Errors don’t crash the REPL - you can continue working after an exception or error occurs.

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Tab Completion

Press Tab to autocomplete:
  • Variable names: $my → $myVariable
  • Function names: array_ → shows all array functions
  • Class names: Date → DateTime, DateTimeZone, etc.
  • Object methods: $obj-> → shows all methods
  • Constants: PHP_ → shows PHP constants
>>> $datetime = new DateTime();
>>> $datetime->[TAB]
# Shows: add, createFromFormat, diff, format, getTimezone, modify, setDate, ...

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Configuration

PsySH looks for configuration in:
  • ~/.config/psysh/config.php
  • ~/.psysh/rc.php
  • .psysh.php in the current directory (project-specific)

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Example Configuration

<?php
// ~/.config/psysh/config.php

return [
    'defaultIncludes' => [
        __DIR__ . '/bootstrap.php',
    ],
    'startupMessage' => 'Welcome to my custom PsySH!',
    'requireSemicolons' => false,
    'useUnicode' => true,
];
Run psysh --info to see your current configuration and environment details.

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Interactive vs Non-Interactive Mode

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Non-Interactive Mode

Execute PHP code from stdin: 
echo '<?php echo 2 + 2;' | psysh
# Output: 4

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Raw Output Mode

Use --raw-output for machine-readable output: 
echo '<?php ["a", "b", "c"];' | psysh --raw-output
# Output: array (0 => 'a', 1 => 'b', 2 => 'c')

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Working Directory

Set the working directory when starting PsySH: 
psysh --cwd /path/to/project
This is useful when your project’s autoloader or configuration depends on the working directory.

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Input Validation

By default, PsySH validates and cleans your input before execution. This can be disabled with the --yolo flag: 
psysh --yolo
The --yolo flag disables input validation. This can lead to unexpected behavior and is not recommended for normal use.

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