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Start an interactive REPL (Read-Eval-Print Loop) to try out and test Cerbos condition expressions. This is useful for experimenting with CEL (Common Expression Language) expressions used in policy conditions.

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Usage

cerbos repl [flags]

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Description

The REPL provides an interactive environment where you can:
  • Test CEL expressions used in policy conditions
  • Experiment with Cerbos-specific functions and variables
  • Validate expression syntax before using them in policies
  • Learn CEL syntax interactively
The REPL supports multi-line input and maintains a history of commands for easy recall.

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Flags

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--history
string
Path to history file for storing command historyIf not specified, history is stored in the default user data directory

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Interactive Commands

Once in the REPL, you can use the following:
  • Enter expressions: Type any valid CEL expression and press Enter
  • Multi-line mode: The REPL automatically detects incomplete expressions
  • Ctrl+C: Exit the REPL
  • Up/Down arrows: Navigate command history
  • Tab completion: Auto-complete function names and variables

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Examples

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Start the REPL

cerbos repl

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Test a simple expression

Cerbos REPL
> 2 + 2
4

> "hello" + " " + "world"
"hello world"

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Test condition expressions

> request.resource.attr.owner == "john"
true

> request.principal.attr.role in ["admin", "manager"]
true

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Test Cerbos functions

> hierarchy("acme.corp.engineering")
["acme.corp.engineering", "acme.corp", "acme"]

> timeSince(timestamp("2024-01-01T00:00:00Z"))
duration("720h")

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Test complex conditions

> request.resource.attr.status == "pending" && 
  request.principal.attr.department == request.resource.attr.department
true

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Available Variables

The REPL provides access to common request context variables:
  • request.principal - Principal (user) information
  • request.resource - Resource being accessed
  • request.auxData - Auxiliary data from the request
  • variables - Exported variables from policies

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Available Functions

All Cerbos CEL functions are available in the REPL:

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Standard CEL Functions

  • String manipulation: contains(), startsWith(), endsWith(), matches()
  • Collection operations: size(), in, all(), exists(), filter(), map()
  • Arithmetic: +, -, *, /, %
  • Comparison: ==, !=, <, <=, >, >=
  • Logical: &&, ||, !

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Cerbos-Specific Functions

  • hierarchy() - Generate scope hierarchy
  • timeSince() - Calculate time since a timestamp
  • now() - Current timestamp
  • timestamp() - Parse timestamp string

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History

Command history is automatically saved and persisted between sessions. The default location is:
  • Linux/macOS: ~/.local/share/cerbos/repl_history
  • Windows: %LOCALAPPDATA%\cerbos\repl_history

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Use Cases

Test condition expressions before adding them to your policies to ensure they work as expected.
Reproduce and test specific condition logic that may be causing unexpected authorization decisions.
Experiment with CEL syntax and functions in an interactive environment without needing to write full policies.
Verify that complex expressions evaluate correctly with different input values.

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Notes

The REPL evaluates expressions in isolation. It does not have access to actual policies or make authorization decisions - it only evaluates the expressions you enter.
Use the REPL to test conditions before adding them to your policies. This helps catch syntax errors and logic issues early.